{"schemaVersion":"1.0","revision":"fa961ab24277a91737c3","article":{"id":"scwiki-g5","topicId":"scwiki-topic-g5","code":"G5","slug":"jaccarino-peter-effect","title":"Jaccarino–Peter effect: exchange compensation and its evidence","summary":"Understand signed exchange compensation, NMR evidence and orbital limits without confusing high-field superconductivity with proof of one mechanism.","aliases":["Jaccarino-Peter effect","exchange compensation","negative exchange field","JP effect","NMR compensation field"],"evidenceTypes":["theory","experimental"],"relatedCodes":["G3","G4","G2","D5"],"editorialStatus":"scoped-check","contentState":"pilot","modifiedAt":"2026-10-18T16:13:01.109773+00:00","review":{"checkedAt":"2026-10-18","scope":"Historical publisher records, selected original organic transport and NMR evidence, inherited scoped nickelate review and independent shift/energy examples.","limitations":["Complete scientific acceptance remains open.","Wu author calibration sign mismatch and excluded systematic uncertainty remain unresolved; final full-text comparison open.","Exchange estimates are attributed inferences, not independent raw-spectrum reproductions.","Compensation does not remove orbital pair breaking or alone establish superconductivity."]},"provenance":{"repository":"JackZH26/jzis-superconductivity","commit":"0a7c9d6696804ec26aa12f8eed68b55c9b3c0fcf","path":"G_magnetism_interplay/G5_Jaccarino_Peter_effect.md","sha256":"f7d671b50e5e4f9221acad24e3205b36e6f7e316d52c449e9c66e977cfc8fa5a","sourceId":"file-655ac228221b126d"},"references":[{"id":"source-849f7f4f675464de","doi":"10.1103/PhysRevLett.9.290","title":"Ultra-High-Field Superconductivity","year":1962,"url":"https://doi.org/10.1103/PhysRevLett.9.290","publicationStatus":"journal-article","verification":{"scope":"publisher-identity-only","checkedAt":"2026-10-18","evidenceUrl":"https://journals.aps.org/prl/abstract/10.1103/PhysRevLett.9.290","note":"Published1October1962. Original identity verified; full text unavailable. Independent field-budget illustration is not a reproduction of the original derivation."}},{"id":"source-d564bee026e788c7","doi":"10.1103/PhysRevLett.53.497","title":"Observation of Magnetic-Field-Induced Superconductivity","year":1984,"url":"https://doi.org/10.1103/PhysRevLett.53.497","publicationStatus":"journal-article","verification":{"scope":"original-publisher-abstract","checkedAt":"2026-10-18","evidenceUrl":"https://journals.aps.org/prl/abstract/10.1103/PhysRevLett.53.497","note":"Published30July1984. Original abstract confirms Eu-Sn molybdenum chalcogenide family and compensation interpretation. Exact composition, curves and full methods not checked."}},{"id":"source-7d153b141f652513","doi":"10.1103/PhysRevLett.87.067002","title":"Superconductivity in an Organic Insulator at Very High Magnetic Fields","year":2001,"url":"https://doi.org/10.1103/PhysRevLett.87.067002","publicationStatus":"journal-article","verification":{"scope":"selected-primary-text-and-figure","checkedAt":"2026-10-18","evidenceUrl":"https://arxiv.org/pdf/cond-mat/0103463v1","note":"Published19July2001 verified in original publisher record, distinct from6August issue. Authorv1 dated22March2001 selectedpp1–3 text andp4Figures1–3 visually checked. Final-version comparison and raw transport/noise calibration open."}},{"id":"source-473d207bc401a7e7","doi":"10.1143/JPSJ.76.124708","title":"77Se NMR Evidence for the Jaccarino–Peter Mechanism in the Field Induced Superconductor, lambda-(BETS)2FeCl4","year":2007,"url":"https://doi.org/10.1143/JPSJ.76.124708","publicationStatus":"journal-article","verification":{"scope":"selected-primary-text-and-figure","checkedAt":"2026-10-18","evidenceUrl":"https://arxiv.org/pdf/0708.2654v1","note":"Authorv1 dated20August2007 selectedpp1–6,10–12 andp11Figure8 visually checked. Published15December2007 verified in original J-STAGE indexed record; 2010availability is not publication. Internal2018typesetting date is not publication. Full final/rawfit calibration open."}},{"id":"source-f328f3068f201541","doi":"10.1103/PhysRevB.76.132510","title":"77Se NMR measurements of the pi-d exchange field in the organic conductor lambda-(BETS)2FeCl4","year":2007,"url":"https://doi.org/10.1103/PhysRevB.76.132510","publicationStatus":"journal-article","verification":{"scope":"selected-primary-text-and-figure","checkedAt":"2026-10-18","evidenceUrl":"https://arxiv.org/pdf/0706.0933v1","note":"Published26October2007 originalpublisherabstract checked. Authorv1 dated7June2007 selectedpp1–4; p4equations11–12 and calibration visually checked. Signed input mismatch and omitted Kax systematic uncertainty unresolved; no independent reproduction or finalfulltext comparison."}},{"id":"source-3504ee9027165d0a","doi":"10.1038/s41586-026-10547-y","title":"Field re-entrant superconductivity in Eu-doped infinite-layer nickelates","year":2026,"url":"https://doi.org/10.1038/s41586-026-10547-y","publicationStatus":"journal-article","verification":{"scope":"selected-author-text-and-figures","checkedAt":"2026-10-18","evidenceUrl":"https://arxiv.org/pdf/2508.14666v3","note":"Published23April2026; read authorv3 dated25April2026, selectedpp2–8, captionsp12, methodsp13–14; Fig2p19/Fig3p20 visually checked. Full final equivalence, calibration and all raw data remain open."}},{"id":"source-b57e3b2b5a90705f","doi":"10.1038/s41467-026-74065-1","title":"Paramagnetically driven superconducting re-entrance in Eu-doped infinite layer nickelates","year":2026,"url":"https://doi.org/10.1038/s41467-026-74065-1","publicationStatus":"journal-article","verification":{"scope":"selected-final-text-and-figure","checkedAt":"2026-10-18","evidenceUrl":"https://www.nature.com/articles/s41467-026-74065-1.pdf","note":"Published19June2026, distinct from27May acceptance. Final9-page PDF selectedpp1–4 read; p4Fig3 visually checked. Two substrates and different field-facility specimens distinguished. Full supplementary data and model fitting unchecked."}}],"claims":[{"id":"scwiki-g5-claim-scope-1","sectionId":"scope","statement":"The Jaccarino–Peter effect is compensation of the spin-splitting field experienced by conduction electrons. An exchange contribution opposite to the applied field can reduce Zeeman pair breaking near a finite field. It does not cancel the applied field everywhere in space or remove orbital coupling. A large critical field, a second superconducting pocket or the presence of magnetic ions alone does not establish this mechanism. The original proposal dates to 1962; its identity is verified here, but its full derivation has not been reread.","evidenceType":"experimental","sourceIds":["source-849f7f4f675464de","source-7d153b141f652513"],"conditions":"Explicit exchange convention, applied field, temperature, corrected-shift assumptions and probe-specific limits; synthetic examples are not material fits.","verificationScope":"Selected primary evidence and independent bounded examples; complete scientific acceptance remains open."},{"id":"scwiki-g5-claim-scope-2","sectionId":"scope","statement":"Meul and colleagues' 1984 work reports field-induced superconductivity in a Eu–Sn molybdenum chalcogenide system and interprets it through compensation. The original abstract supports that historical connection. Exact composition, numerical field endpoints and complete measurement methods have not been verified here, so they are not promoted to universal material parameters. A classical example cannot supply the missing exchange measurement for a different compound.","evidenceType":"experimental","sourceIds":["source-d564bee026e788c7"],"conditions":"Explicit exchange convention, applied field, temperature, corrected-shift assumptions and probe-specific limits; synthetic examples are not material fits.","verificationScope":"Selected primary evidence and independent bounded examples; complete scientific acceptance remains open."},{"id":"scwiki-g5-claim-mathematical-assumptions-1","sectionId":"mathematical-assumptions","statement":"Choose the positive direction along the applied field and define the signed effective field as $B_{\\mathrm{eff}}=B_{\\mathrm{ext}}+B_{\\mathrm{ex}}$. Compensation requires $B_{\\mathrm{ex}}\\lt0$ in this convention. In the collinear single-band illustration, spin energies are $E_\\pm=\\pm h$, with $h=g\\mu_B B_{\\mathrm{eff}}/2$ and positive $g$. Their full separation is $2|h|=g\\mu_B|B_{\\mathrm{eff}}|$. A source using another sign for its exchange constant must first be translated into this convention; the sign of a symbol called J is not transferable without its Hamiltonian.","evidenceType":"theory","sourceIds":["source-849f7f4f675464de","source-7d153b141f652513"],"conditions":"Explicit exchange convention, applied field, temperature, corrected-shift assumptions and probe-specific limits; synthetic examples are not material fits.","verificationScope":"Selected primary evidence and independent bounded examples; complete scientific acceptance remains open."},{"id":"scwiki-g5-claim-mathematical-assumptions-2","sectionId":"mathematical-assumptions","statement":"An independent synthetic example isolates an inference used in shift measurements. Suppose corrected frequency shifts obey $y=m(B-B_*)$, with nonzero, field-independent slope and a saturated exchange contribution. A fitted line $y=mB+c$ gives $B_*=-c/m$. Four imposed fields, 14.5, 21, 26 and 28 T, recover six noiseless examples with target intercepts of 20, 32 and 40 T and both slope signs. The latter two targets are extrapolations outside this measurement interval. These calculations reproduce the algebra, not published spectra.","evidenceType":"theory","sourceIds":["source-473d207bc401a7e7"],"conditions":"Explicit exchange convention, applied field, temperature, corrected-shift assumptions and probe-specific limits; synthetic examples are not material fits.","verificationScope":"Selected primary evidence and independent bounded examples; complete scientific acceptance remains open."},{"id":"scwiki-g5-claim-mathematical-assumptions-3","sectionId":"mathematical-assumptions","statement":"A residual constant correction $d$ moves the inferred intercept by $-d/m$. In the synthetic examples, a 0.06 MHz offset shifts it by +2 T for a slope of -0.03 MHz/T, or by -1.2 T for +0.05 MHz/T. A zero slope leaves the intercept unidentifiable. Nine separate spin-energy checks verify the distinction between half splitting and full splitting, including negative effective fields. Neither exercise contains orbital coupling, spin-flip scattering or a gap equation, so neither demonstrates a superconducting transition.","evidenceType":"theory","sourceIds":["source-473d207bc401a7e7","source-f328f3068f201541"],"conditions":"Explicit exchange convention, applied field, temperature, corrected-shift assumptions and probe-specific limits; synthetic examples are not material fits.","verificationScope":"Selected primary evidence and independent bounded examples; complete scientific acceptance remains open."},{"id":"scwiki-g5-claim-experimental-criteria-1","sectionId":"experimental-criteria","statement":"Balicas and colleagues measured four-terminal transport in lambda-(BETS)2FeCl4 with field near the conducting plane. Their phase diagram distinguishes resistive midpoints from resistance below instrumental sensitivity; the broad 18–41 T field-induced region is not uniformly a zero-resistance region. Below 2 K, resistance reaches the experimental zero near 33 T. Tilting introduces a transverse component that suppresses the state. Figure 3's pairing-state curves are theoretical fits, not direct imaging of a modulated order parameter. These results support a compensation interpretation while retaining orbital and measurement limits.","evidenceType":"experimental","sourceIds":["source-7d153b141f652513"],"conditions":"Explicit exchange convention, applied field, temperature, corrected-shift assumptions and probe-specific limits; synthetic examples are not material fits.","verificationScope":"Selected primary evidence and independent bounded examples; complete scientific acceptance remains open."},{"id":"scwiki-g5-claim-experimental-criteria-2","sectionId":"experimental-criteria","statement":"Hiraki and colleagues provide a different probe: corrected 77Se NMR shifts in the metallic state at 1.5 K and fields up to 28 T. They infer an exchange-field magnitude of 32 ± 2 T by extrapolating a field-dependent shift. This is not an observed zero crossing at 32 T. Chemical, dipolar and demagnetization corrections enter the analysis; demagnetization dominates their stated uncertainty. The interpretation assumes sufficiently saturated local moments and suitable field-independent electronic response. The transport specimen discussed alongside the NMR came from the same batch, not necessarily the identical crystal.","evidenceType":"experimental","sourceIds":["source-473d207bc401a7e7"],"conditions":"Explicit exchange convention, applied field, temperature, corrected-shift assumptions and probe-specific limits; synthetic examples are not material fits.","verificationScope":"Selected primary evidence and independent bounded examples; complete scientific acceptance remains open."},{"id":"scwiki-g5-claim-experimental-criteria-3","sectionId":"experimental-criteria","statement":"Wu and colleagues instead infer an exchange field of -32.7 ± 1.5 T from a 9 T, 5 K angular-shift experiment. Their author manuscript uses a hyperfine calibration partly informed by the nonmagnetic Ga analogue, and explicitly excludes an unknown uncertainty in its axial Knight-shift coefficient. Its predicted value at 33 T is a further model adjustment. Keep the applied field, temperature, inferred exchange field and uncertainty scope separate; the quoted exchange magnitude is not the applied field at which these spectra were taken.","evidenceType":"experimental","sourceIds":["source-f328f3068f201541"],"conditions":"Explicit exchange convention, applied field, temperature, corrected-shift assumptions and probe-specific limits; synthetic examples are not material fits.","verificationScope":"Selected primary evidence and independent bounded examples; complete scientific acceptance remains open."},{"id":"scwiki-g5-claim-experimental-criteria-4","sectionId":"experimental-criteria","statement":"For a new material, the evidence should connect a measured local-moment response to a signed electronic exchange contribution, then test whether its field and angle dependence account for the superconducting observations. Compare transport with independent magnetic or thermodynamic evidence where available. Different samples, transition criteria, pressure conditions and temperatures must remain identifiable. A numerical similarity between a resistance minimum and an inferred exchange field is supporting evidence, not a replacement for calibration or alternative-mechanism tests.","evidenceType":"experimental","sourceIds":["source-7d153b141f652513","source-473d207bc401a7e7","source-f328f3068f201541"],"conditions":"Explicit exchange convention, applied field, temperature, corrected-shift assumptions and probe-specific limits; synthetic examples are not material fits.","verificationScope":"Selected primary evidence and independent bounded examples; complete scientific acceptance remains open."},{"id":"scwiki-g5-claim-limits-and-disputes-1","sectionId":"limits-and-disputes","statement":"The selected Wu author manuscript has a convention issue requiring further review: the signed angular-difference formula and the subsequent printed numerical input do not match under direct substitution. The final publisher abstract confirms the reported exchange value, but the full final calibration has not been compared. This page therefore attributes the value to the authors and does not claim to reproduce it independently. The discrepancy is an unresolved source-version issue, not evidence that the experimental phenomenon is false. Complete scientific acceptance remains open.","evidenceType":"experimental","sourceIds":["source-f328f3068f201541"],"conditions":"Explicit exchange convention, applied field, temperature, corrected-shift assumptions and probe-specific limits; synthetic examples are not material fits.","verificationScope":"Selected primary evidence and independent bounded examples; complete scientific acceptance remains open."},{"id":"scwiki-g5-claim-limits-and-disputes-2","sectionId":"limits-and-disputes","statement":"The 2026 Eu-rich Sm/Ca/Eu nickelate study reports reentrance and discusses exchange compensation alongside other magnetic physics. Its selected later author version leaves the magnetic order unresolved and includes sample-dependent angular behavior. It does not justify a universal claim of established ferromagnetism or triplet pairing. A separate Nd/Eu nickelate study develops a paramagnetic-compensation interpretation using different material and substrate conditions. Their similarities motivate tests; they do not make the two systems interchangeable or establish one uniquely complete mechanism.","evidenceType":"experimental","sourceIds":["source-3504ee9027165d0a","source-b57e3b2b5a90705f"],"conditions":"Explicit exchange convention, applied field, temperature, corrected-shift assumptions and probe-specific limits; synthetic examples are not material fits.","verificationScope":"Selected primary evidence and independent bounded examples; complete scientific acceptance remains open."},{"id":"scwiki-g5-claim-discovery-implications-1","sectionId":"discovery-implications","statement":"Store the exchange-field estimate with its sign convention, probe, applied field, temperature, correction model and uncertainty coverage. Record whether compensation was measured directly, extrapolated or assumed in fitting a phase boundary. Separate those records from superconducting transition temperatures. For multiband systems, test whether one effective exchange field is adequate rather than assuming every band has the same coupling. Preserve the independently measured orbital constraints when evaluating candidate compensation windows.","evidenceType":"experimental","sourceIds":["source-473d207bc401a7e7","source-f328f3068f201541","source-3504ee9027165d0a"],"conditions":"Explicit exchange convention, applied field, temperature, corrected-shift assumptions and probe-specific limits; synthetic examples are not material fits.","verificationScope":"Selected primary evidence and independent bounded examples; complete scientific acceptance remains open."}],"corrections":[],"equationChecks":[{"targetSectionId":"mathematical-assumptions","tex":"B_*=-c/m","check":"6synthetic slope/intercept cases with offset bias verified; zero-slope rejected, extrapolation labelled."},{"targetSectionId":"mathematical-assumptions","tex":"2|h|=g\\mu_B|B_{\\mathrm{eff}}|","check":"9energy-level cases including positive,negative,zero effective fields verified."}],"materialCases":[{"id":"scwiki-g5-material-1","formula":"lambda-(BETS)2FeCl4","sample":"Wu 9T angular NMR experiment","recordType":"experiment","reportedTemperatureK":5,"tcK":null,"temperatureKind":"normal-state","temperatureNote":"NMR measurement temperature at9T; exchange estimate is not a superconductingTc.","criterion":"NMR-exchange-inference","pressureRegime":"ambient","pressureGPa":null,"equilibrium":"unknown","probe":"77Se angular NMR shift with hyperfine/dipolar calibration","sourceId":"source-f328f3068f201541","aliases":[]}],"sourceMap":[{"startLine":1,"endLine":106,"targetSections":["scope","mathematical-assumptions","experimental-criteria","limits-and-disputes","discovery-implications","related-topics"],"decision":"edited-with-scoped-evidence","note":"Pinned original preserved; remove unverified exacthistoricalwindow and stale magneticorder/angular claims; add independently checkedNMR evidence and convention limits."}],"body":"## Scope\n\nThe Jaccarino–Peter effect is compensation of the spin-splitting field experienced by conduction electrons. An exchange contribution opposite to the applied field can reduce Zeeman pair breaking near a finite field. It does not cancel the applied field everywhere in space or remove orbital coupling. A large critical field, a second superconducting pocket or the presence of magnetic ions alone does not establish this mechanism. The original proposal dates to 1962; its identity is verified here, but its full derivation has not been reread. [R1](#ref-source-849f7f4f675464de) [R3](#ref-source-7d153b141f652513)\n\nMeul and colleagues' 1984 work reports field-induced superconductivity in a Eu–Sn molybdenum chalcogenide system and interprets it through compensation. The original abstract supports that historical connection. Exact composition, numerical field endpoints and complete measurement methods have not been verified here, so they are not promoted to universal material parameters. A classical example cannot supply the missing exchange measurement for a different compound. [R2](#ref-source-d564bee026e788c7)\n\n## Mathematical assumptions\n\nChoose the positive direction along the applied field and define the signed effective field as $B_{\\mathrm{eff}}=B_{\\mathrm{ext}}+B_{\\mathrm{ex}}$. Compensation requires $B_{\\mathrm{ex}}\\lt0$ in this convention. In the collinear single-band illustration, spin energies are $E_\\pm=\\pm h$, with $h=g\\mu_B B_{\\mathrm{eff}}/2$ and positive $g$. Their full separation is $2|h|=g\\mu_B|B_{\\mathrm{eff}}|$. A source using another sign for its exchange constant must first be translated into this convention; the sign of a symbol called J is not transferable without its Hamiltonian. [R1](#ref-source-849f7f4f675464de) [R3](#ref-source-7d153b141f652513)\n\nAn independent synthetic example isolates an inference used in shift measurements. Suppose corrected frequency shifts obey $y=m(B-B_*)$, with nonzero, field-independent slope and a saturated exchange contribution. A fitted line $y=mB+c$ gives $B_*=-c/m$. Four imposed fields, 14.5, 21, 26 and 28 T, recover six noiseless examples with target intercepts of 20, 32 and 40 T and both slope signs. The latter two targets are extrapolations outside this measurement interval. These calculations reproduce the algebra, not published spectra. [R4](#ref-source-473d207bc401a7e7)\n\nA residual constant correction $d$ moves the inferred intercept by $-d/m$. In the synthetic examples, a 0.06 MHz offset shifts it by +2 T for a slope of -0.03 MHz/T, or by -1.2 T for +0.05 MHz/T. A zero slope leaves the intercept unidentifiable. Nine separate spin-energy checks verify the distinction between half splitting and full splitting, including negative effective fields. Neither exercise contains orbital coupling, spin-flip scattering or a gap equation, so neither demonstrates a superconducting transition. [R4](#ref-source-473d207bc401a7e7) [R5](#ref-source-f328f3068f201541)\n\n## Experimental criteria\n\nBalicas and colleagues measured four-terminal transport in lambda-(BETS)2FeCl4 with field near the conducting plane. Their phase diagram distinguishes resistive midpoints from resistance below instrumental sensitivity; the broad 18–41 T field-induced region is not uniformly a zero-resistance region. Below 2 K, resistance reaches the experimental zero near 33 T. Tilting introduces a transverse component that suppresses the state. Figure 3's pairing-state curves are theoretical fits, not direct imaging of a modulated order parameter. These results support a compensation interpretation while retaining orbital and measurement limits. [R3](#ref-source-7d153b141f652513)\n\nHiraki and colleagues provide a different probe: corrected 77Se NMR shifts in the metallic state at 1.5 K and fields up to 28 T. They infer an exchange-field magnitude of 32 ± 2 T by extrapolating a field-dependent shift. This is not an observed zero crossing at 32 T. Chemical, dipolar and demagnetization corrections enter the analysis; demagnetization dominates their stated uncertainty. The interpretation assumes sufficiently saturated local moments and suitable field-independent electronic response. The transport specimen discussed alongside the NMR came from the same batch, not necessarily the identical crystal. [R4](#ref-source-473d207bc401a7e7)\n\nWu and colleagues instead infer an exchange field of -32.7 ± 1.5 T from a 9 T, 5 K angular-shift experiment. Their author manuscript uses a hyperfine calibration partly informed by the nonmagnetic Ga analogue, and explicitly excludes an unknown uncertainty in its axial Knight-shift coefficient. Its predicted value at 33 T is a further model adjustment. Keep the applied field, temperature, inferred exchange field and uncertainty scope separate; the quoted exchange magnitude is not the applied field at which these spectra were taken. [R5](#ref-source-f328f3068f201541)\n\nFor a new material, the evidence should connect a measured local-moment response to a signed electronic exchange contribution, then test whether its field and angle dependence account for the superconducting observations. Compare transport with independent magnetic or thermodynamic evidence where available. Different samples, transition criteria, pressure conditions and temperatures must remain identifiable. A numerical similarity between a resistance minimum and an inferred exchange field is supporting evidence, not a replacement for calibration or alternative-mechanism tests. [R3](#ref-source-7d153b141f652513) [R4](#ref-source-473d207bc401a7e7) [R5](#ref-source-f328f3068f201541)\n\n## Limits and disputes\n\nThe selected Wu author manuscript has a convention issue requiring further review: the signed angular-difference formula and the subsequent printed numerical input do not match under direct substitution. The final publisher abstract confirms the reported exchange value, but the full final calibration has not been compared. This page therefore attributes the value to the authors and does not claim to reproduce it independently. The discrepancy is an unresolved source-version issue, not evidence that the experimental phenomenon is false. Complete scientific acceptance remains open. [R5](#ref-source-f328f3068f201541)\n\nThe 2026 Eu-rich Sm/Ca/Eu nickelate study reports reentrance and discusses exchange compensation alongside other magnetic physics. Its selected later author version leaves the magnetic order unresolved and includes sample-dependent angular behavior. It does not justify a universal claim of established ferromagnetism or triplet pairing. A separate Nd/Eu nickelate study develops a paramagnetic-compensation interpretation using different material and substrate conditions. Their similarities motivate tests; they do not make the two systems interchangeable or establish one uniquely complete mechanism. [R6](#ref-source-3504ee9027165d0a) [R7](#ref-source-b57e3b2b5a90705f)\n\n## Discovery implications\n\nStore the exchange-field estimate with its sign convention, probe, applied field, temperature, correction model and uncertainty coverage. Record whether compensation was measured directly, extrapolated or assumed in fitting a phase boundary. Separate those records from superconducting transition temperatures. For multiband systems, test whether one effective exchange field is adequate rather than assuming every band has the same coupling. Preserve the independently measured orbital constraints when evaluating candidate compensation windows. [R4](#ref-source-473d207bc401a7e7) [R5](#ref-source-f328f3068f201541) [R6](#ref-source-3504ee9027165d0a)\n\n## Related topics\n\n[Field-induced superconductivity](/scwiki/field-induced-superconductivity), [reentrant superconductivity](/scwiki/reentrant-superconductivity), [ferromagnetism and superconductivity](/scwiki/ferromagnetism-and-superconductivity), and [nickelates](/scwiki/nickelates).","revision":"181c58dcf6e6ef6fa7de","sections":[{"id":"scope","title":"Scope","markdown":"## Scope\n\nThe Jaccarino–Peter effect is compensation of the spin-splitting field experienced by conduction electrons. An exchange contribution opposite to the applied field can reduce Zeeman pair breaking near a finite field. It does not cancel the applied field everywhere in space or remove orbital coupling. A large critical field, a second superconducting pocket or the presence of magnetic ions alone does not establish this mechanism. The original proposal dates to 1962; its identity is verified here, but its full derivation has not been reread. [R1](#ref-source-849f7f4f675464de) [R3](#ref-source-7d153b141f652513)\n\nMeul and colleagues' 1984 work reports field-induced superconductivity in a Eu–Sn molybdenum chalcogenide system and interprets it through compensation. The original abstract supports that historical connection. Exact composition, numerical field endpoints and complete measurement methods have not been verified here, so they are not promoted to universal material parameters. A classical example cannot supply the missing exchange measurement for a different compound. [R2](#ref-source-d564bee026e788c7)"},{"id":"mathematical-assumptions","title":"Mathematical assumptions","markdown":"## Mathematical assumptions\n\nChoose the positive direction along the applied field and define the signed effective field as $B_{\\mathrm{eff}}=B_{\\mathrm{ext}}+B_{\\mathrm{ex}}$. Compensation requires $B_{\\mathrm{ex}}\\lt0$ in this convention. In the collinear single-band illustration, spin energies are $E_\\pm=\\pm h$, with $h=g\\mu_B B_{\\mathrm{eff}}/2$ and positive $g$. Their full separation is $2|h|=g\\mu_B|B_{\\mathrm{eff}}|$. A source using another sign for its exchange constant must first be translated into this convention; the sign of a symbol called J is not transferable without its Hamiltonian. [R1](#ref-source-849f7f4f675464de) [R3](#ref-source-7d153b141f652513)\n\nAn independent synthetic example isolates an inference used in shift measurements. Suppose corrected frequency shifts obey $y=m(B-B_*)$, with nonzero, field-independent slope and a saturated exchange contribution. A fitted line $y=mB+c$ gives $B_*=-c/m$. Four imposed fields, 14.5, 21, 26 and 28 T, recover six noiseless examples with target intercepts of 20, 32 and 40 T and both slope signs. The latter two targets are extrapolations outside this measurement interval. These calculations reproduce the algebra, not published spectra. [R4](#ref-source-473d207bc401a7e7)\n\nA residual constant correction $d$ moves the inferred intercept by $-d/m$. In the synthetic examples, a 0.06 MHz offset shifts it by +2 T for a slope of -0.03 MHz/T, or by -1.2 T for +0.05 MHz/T. A zero slope leaves the intercept unidentifiable. Nine separate spin-energy checks verify the distinction between half splitting and full splitting, including negative effective fields. Neither exercise contains orbital coupling, spin-flip scattering or a gap equation, so neither demonstrates a superconducting transition. [R4](#ref-source-473d207bc401a7e7) [R5](#ref-source-f328f3068f201541)"},{"id":"experimental-criteria","title":"Experimental criteria","markdown":"## Experimental criteria\n\nBalicas and colleagues measured four-terminal transport in lambda-(BETS)2FeCl4 with field near the conducting plane. Their phase diagram distinguishes resistive midpoints from resistance below instrumental sensitivity; the broad 18–41 T field-induced region is not uniformly a zero-resistance region. Below 2 K, resistance reaches the experimental zero near 33 T. Tilting introduces a transverse component that suppresses the state. Figure 3's pairing-state curves are theoretical fits, not direct imaging of a modulated order parameter. These results support a compensation interpretation while retaining orbital and measurement limits. [R3](#ref-source-7d153b141f652513)\n\nHiraki and colleagues provide a different probe: corrected 77Se NMR shifts in the metallic state at 1.5 K and fields up to 28 T. They infer an exchange-field magnitude of 32 ± 2 T by extrapolating a field-dependent shift. This is not an observed zero crossing at 32 T. Chemical, dipolar and demagnetization corrections enter the analysis; demagnetization dominates their stated uncertainty. The interpretation assumes sufficiently saturated local moments and suitable field-independent electronic response. The transport specimen discussed alongside the NMR came from the same batch, not necessarily the identical crystal. [R4](#ref-source-473d207bc401a7e7)\n\nWu and colleagues instead infer an exchange field of -32.7 ± 1.5 T from a 9 T, 5 K angular-shift experiment. Their author manuscript uses a hyperfine calibration partly informed by the nonmagnetic Ga analogue, and explicitly excludes an unknown uncertainty in its axial Knight-shift coefficient. Its predicted value at 33 T is a further model adjustment. Keep the applied field, temperature, inferred exchange field and uncertainty scope separate; the quoted exchange magnitude is not the applied field at which these spectra were taken. [R5](#ref-source-f328f3068f201541)\n\nFor a new material, the evidence should connect a measured local-moment response to a signed electronic exchange contribution, then test whether its field and angle dependence account for the superconducting observations. Compare transport with independent magnetic or thermodynamic evidence where available. Different samples, transition criteria, pressure conditions and temperatures must remain identifiable. A numerical similarity between a resistance minimum and an inferred exchange field is supporting evidence, not a replacement for calibration or alternative-mechanism tests. [R3](#ref-source-7d153b141f652513) [R4](#ref-source-473d207bc401a7e7) [R5](#ref-source-f328f3068f201541)"},{"id":"limits-and-disputes","title":"Limits and disputes","markdown":"## Limits and disputes\n\nThe selected Wu author manuscript has a convention issue requiring further review: the signed angular-difference formula and the subsequent printed numerical input do not match under direct substitution. The final publisher abstract confirms the reported exchange value, but the full final calibration has not been compared. This page therefore attributes the value to the authors and does not claim to reproduce it independently. The discrepancy is an unresolved source-version issue, not evidence that the experimental phenomenon is false. Complete scientific acceptance remains open. [R5](#ref-source-f328f3068f201541)\n\nThe 2026 Eu-rich Sm/Ca/Eu nickelate study reports reentrance and discusses exchange compensation alongside other magnetic physics. Its selected later author version leaves the magnetic order unresolved and includes sample-dependent angular behavior. It does not justify a universal claim of established ferromagnetism or triplet pairing. A separate Nd/Eu nickelate study develops a paramagnetic-compensation interpretation using different material and substrate conditions. Their similarities motivate tests; they do not make the two systems interchangeable or establish one uniquely complete mechanism. [R6](#ref-source-3504ee9027165d0a) [R7](#ref-source-b57e3b2b5a90705f)"},{"id":"discovery-implications","title":"Discovery implications","markdown":"## Discovery implications\n\nStore the exchange-field estimate with its sign convention, probe, applied field, temperature, correction model and uncertainty coverage. Record whether compensation was measured directly, extrapolated or assumed in fitting a phase boundary. Separate those records from superconducting transition temperatures. For multiband systems, test whether one effective exchange field is adequate rather than assuming every band has the same coupling. Preserve the independently measured orbital constraints when evaluating candidate compensation windows. [R4](#ref-source-473d207bc401a7e7) [R5](#ref-source-f328f3068f201541) [R6](#ref-source-3504ee9027165d0a)"},{"id":"related-topics","title":"Related topics","markdown":"## Related topics\n\n[Field-induced superconductivity](/scwiki/field-induced-superconductivity), [reentrant superconductivity](/scwiki/reentrant-superconductivity), [ferromagnetism and superconductivity](/scwiki/ferromagnetism-and-superconductivity), and [nickelates](/scwiki/nickelates)."},{"id":"material-cases","title":"Material cases","markdown":"## Material cases\n\nValues describe individual reports, not a ranking. Unknown means the checked source did not supply the field at this review scope.\n\n| Material and sample | Reported temperature | Criterion | Probe | Pressure | State | Evidence |\n|---|---|---|---|---|---|---|\n| lambda-(BETS)2FeCl4; Wu 9T angular NMR experiment | 5 K; NMR measurement temperature at9T; exchange estimate is not a superconductingTc. | normal-state; NMR-exchange-inference | 77Se angular NMR shift with hyperfine/dipolar calibration | ambient; unknown GPa | unknown | experiment; [source](#ref-source-f328f3068f201541) |"}],"markdown":"# Jaccarino–Peter effect: exchange compensation and its evidence\n\nUnderstand signed exchange compensation, NMR evidence and orbital limits without confusing high-field superconductivity with proof of one mechanism.\n\n## Scope\n\nThe Jaccarino–Peter effect is compensation of the spin-splitting field experienced by conduction electrons. An exchange contribution opposite to the applied field can reduce Zeeman pair breaking near a finite field. It does not cancel the applied field everywhere in space or remove orbital coupling. A large critical field, a second superconducting pocket or the presence of magnetic ions alone does not establish this mechanism. The original proposal dates to 1962; its identity is verified here, but its full derivation has not been reread. [R1](#ref-source-849f7f4f675464de) [R3](#ref-source-7d153b141f652513)\n\nMeul and colleagues' 1984 work reports field-induced superconductivity in a Eu–Sn molybdenum chalcogenide system and interprets it through compensation. The original abstract supports that historical connection. Exact composition, numerical field endpoints and complete measurement methods have not been verified here, so they are not promoted to universal material parameters. A classical example cannot supply the missing exchange measurement for a different compound. [R2](#ref-source-d564bee026e788c7)\n\n## Mathematical assumptions\n\nChoose the positive direction along the applied field and define the signed effective field as $B_{\\mathrm{eff}}=B_{\\mathrm{ext}}+B_{\\mathrm{ex}}$. Compensation requires $B_{\\mathrm{ex}}\\lt0$ in this convention. In the collinear single-band illustration, spin energies are $E_\\pm=\\pm h$, with $h=g\\mu_B B_{\\mathrm{eff}}/2$ and positive $g$. Their full separation is $2|h|=g\\mu_B|B_{\\mathrm{eff}}|$. A source using another sign for its exchange constant must first be translated into this convention; the sign of a symbol called J is not transferable without its Hamiltonian. [R1](#ref-source-849f7f4f675464de) [R3](#ref-source-7d153b141f652513)\n\nAn independent synthetic example isolates an inference used in shift measurements. Suppose corrected frequency shifts obey $y=m(B-B_*)$, with nonzero, field-independent slope and a saturated exchange contribution. A fitted line $y=mB+c$ gives $B_*=-c/m$. Four imposed fields, 14.5, 21, 26 and 28 T, recover six noiseless examples with target intercepts of 20, 32 and 40 T and both slope signs. The latter two targets are extrapolations outside this measurement interval. These calculations reproduce the algebra, not published spectra. [R4](#ref-source-473d207bc401a7e7)\n\nA residual constant correction $d$ moves the inferred intercept by $-d/m$. In the synthetic examples, a 0.06 MHz offset shifts it by +2 T for a slope of -0.03 MHz/T, or by -1.2 T for +0.05 MHz/T. A zero slope leaves the intercept unidentifiable. Nine separate spin-energy checks verify the distinction between half splitting and full splitting, including negative effective fields. Neither exercise contains orbital coupling, spin-flip scattering or a gap equation, so neither demonstrates a superconducting transition. [R4](#ref-source-473d207bc401a7e7) [R5](#ref-source-f328f3068f201541)\n\n## Experimental criteria\n\nBalicas and colleagues measured four-terminal transport in lambda-(BETS)2FeCl4 with field near the conducting plane. Their phase diagram distinguishes resistive midpoints from resistance below instrumental sensitivity; the broad 18–41 T field-induced region is not uniformly a zero-resistance region. Below 2 K, resistance reaches the experimental zero near 33 T. Tilting introduces a transverse component that suppresses the state. Figure 3's pairing-state curves are theoretical fits, not direct imaging of a modulated order parameter. These results support a compensation interpretation while retaining orbital and measurement limits. [R3](#ref-source-7d153b141f652513)\n\nHiraki and colleagues provide a different probe: corrected 77Se NMR shifts in the metallic state at 1.5 K and fields up to 28 T. They infer an exchange-field magnitude of 32 ± 2 T by extrapolating a field-dependent shift. This is not an observed zero crossing at 32 T. Chemical, dipolar and demagnetization corrections enter the analysis; demagnetization dominates their stated uncertainty. The interpretation assumes sufficiently saturated local moments and suitable field-independent electronic response. The transport specimen discussed alongside the NMR came from the same batch, not necessarily the identical crystal. [R4](#ref-source-473d207bc401a7e7)\n\nWu and colleagues instead infer an exchange field of -32.7 ± 1.5 T from a 9 T, 5 K angular-shift experiment. Their author manuscript uses a hyperfine calibration partly informed by the nonmagnetic Ga analogue, and explicitly excludes an unknown uncertainty in its axial Knight-shift coefficient. Its predicted value at 33 T is a further model adjustment. Keep the applied field, temperature, inferred exchange field and uncertainty scope separate; the quoted exchange magnitude is not the applied field at which these spectra were taken. [R5](#ref-source-f328f3068f201541)\n\nFor a new material, the evidence should connect a measured local-moment response to a signed electronic exchange contribution, then test whether its field and angle dependence account for the superconducting observations. Compare transport with independent magnetic or thermodynamic evidence where available. Different samples, transition criteria, pressure conditions and temperatures must remain identifiable. A numerical similarity between a resistance minimum and an inferred exchange field is supporting evidence, not a replacement for calibration or alternative-mechanism tests. [R3](#ref-source-7d153b141f652513) [R4](#ref-source-473d207bc401a7e7) [R5](#ref-source-f328f3068f201541)\n\n## Limits and disputes\n\nThe selected Wu author manuscript has a convention issue requiring further review: the signed angular-difference formula and the subsequent printed numerical input do not match under direct substitution. The final publisher abstract confirms the reported exchange value, but the full final calibration has not been compared. This page therefore attributes the value to the authors and does not claim to reproduce it independently. The discrepancy is an unresolved source-version issue, not evidence that the experimental phenomenon is false. Complete scientific acceptance remains open. [R5](#ref-source-f328f3068f201541)\n\nThe 2026 Eu-rich Sm/Ca/Eu nickelate study reports reentrance and discusses exchange compensation alongside other magnetic physics. Its selected later author version leaves the magnetic order unresolved and includes sample-dependent angular behavior. It does not justify a universal claim of established ferromagnetism or triplet pairing. A separate Nd/Eu nickelate study develops a paramagnetic-compensation interpretation using different material and substrate conditions. Their similarities motivate tests; they do not make the two systems interchangeable or establish one uniquely complete mechanism. [R6](#ref-source-3504ee9027165d0a) [R7](#ref-source-b57e3b2b5a90705f)\n\n## Discovery implications\n\nStore the exchange-field estimate with its sign convention, probe, applied field, temperature, correction model and uncertainty coverage. Record whether compensation was measured directly, extrapolated or assumed in fitting a phase boundary. Separate those records from superconducting transition temperatures. For multiband systems, test whether one effective exchange field is adequate rather than assuming every band has the same coupling. Preserve the independently measured orbital constraints when evaluating candidate compensation windows. [R4](#ref-source-473d207bc401a7e7) [R5](#ref-source-f328f3068f201541) [R6](#ref-source-3504ee9027165d0a)\n\n## Related topics\n\n[Field-induced superconductivity](/scwiki/field-induced-superconductivity), [reentrant superconductivity](/scwiki/reentrant-superconductivity), [ferromagnetism and superconductivity](/scwiki/ferromagnetism-and-superconductivity), and [nickelates](/scwiki/nickelates).\n\n## Material cases\n\nValues describe individual reports, not a ranking. Unknown means the checked source did not supply the field at this review scope.\n\n| Material and sample | Reported temperature | Criterion | Probe | Pressure | State | Evidence |\n|---|---|---|---|---|---|---|\n| lambda-(BETS)2FeCl4; Wu 9T angular NMR experiment | 5 K; NMR measurement temperature at9T; exchange estimate is not a superconductingTc. | normal-state; NMR-exchange-inference | 77Se angular NMR shift with hyperfine/dipolar calibration | ambient; unknown GPa | unknown | experiment; [source](#ref-source-f328f3068f201541) |\n\n## Sources\n\n### Ref source-849f7f4f675464de\n\n[R1] Ultra-High-Field Superconductivity (1962). [DOI 10.1103/PhysRevLett.9.290](https://doi.org/10.1103/PhysRevLett.9.290). Publication: journal-article. Check: publisher-identity-only. Checked: 2026-10-18. Published1October1962. Original identity verified; full text unavailable. Independent field-budget illustration is not a reproduction of the original derivation.\n### Ref source-d564bee026e788c7\n\n[R2] Observation of Magnetic-Field-Induced Superconductivity (1984). [DOI 10.1103/PhysRevLett.53.497](https://doi.org/10.1103/PhysRevLett.53.497). Publication: journal-article. Check: original-publisher-abstract. Checked: 2026-10-18. Published30July1984. Original abstract confirms Eu-Sn molybdenum chalcogenide family and compensation interpretation. Exact composition, curves and full methods not checked.\n### Ref source-7d153b141f652513\n\n[R3] Superconductivity in an Organic Insulator at Very High Magnetic Fields (2001). [DOI 10.1103/PhysRevLett.87.067002](https://doi.org/10.1103/PhysRevLett.87.067002). Publication: journal-article. Check: selected-primary-text-and-figure. Checked: 2026-10-18. Published19July2001 verified in original publisher record, distinct from6August issue. Authorv1 dated22March2001 selectedpp1–3 text andp4Figures1–3 visually checked. Final-version comparison and raw transport/noise calibration open.\n### Ref source-473d207bc401a7e7\n\n[R4] 77Se NMR Evidence for the Jaccarino–Peter Mechanism in the Field Induced Superconductor, lambda-(BETS)2FeCl4 (2007). [DOI 10.1143/JPSJ.76.124708](https://doi.org/10.1143/JPSJ.76.124708). Publication: journal-article. Check: selected-primary-text-and-figure. Checked: 2026-10-18. Authorv1 dated20August2007 selectedpp1–6,10–12 andp11Figure8 visually checked. Published15December2007 verified in original J-STAGE indexed record; 2010availability is not publication. Internal2018typesetting date is not publication. Full final/rawfit calibration open.\n### Ref source-f328f3068f201541\n\n[R5] 77Se NMR measurements of the pi-d exchange field in the organic conductor lambda-(BETS)2FeCl4 (2007). [DOI 10.1103/PhysRevB.76.132510](https://doi.org/10.1103/PhysRevB.76.132510). Publication: journal-article. Check: selected-primary-text-and-figure. Checked: 2026-10-18. Published26October2007 originalpublisherabstract checked. Authorv1 dated7June2007 selectedpp1–4; p4equations11–12 and calibration visually checked. Signed input mismatch and omitted Kax systematic uncertainty unresolved; no independent reproduction or finalfulltext comparison.\n### Ref source-3504ee9027165d0a\n\n[R6] Field re-entrant superconductivity in Eu-doped infinite-layer nickelates (2026). [DOI 10.1038/s41586-026-10547-y](https://doi.org/10.1038/s41586-026-10547-y). Publication: journal-article. Check: selected-author-text-and-figures. Checked: 2026-10-18. Published23April2026; read authorv3 dated25April2026, selectedpp2–8, captionsp12, methodsp13–14; Fig2p19/Fig3p20 visually checked. Full final equivalence, calibration and all raw data remain open.\n### Ref source-b57e3b2b5a90705f\n\n[R7] Paramagnetically driven superconducting re-entrance in Eu-doped infinite layer nickelates (2026). [DOI 10.1038/s41467-026-74065-1](https://doi.org/10.1038/s41467-026-74065-1). Publication: journal-article. Check: selected-final-text-and-figure. Checked: 2026-10-18. Published19June2026, distinct from27May acceptance. Final9-page PDF selectedpp1–4 read; p4Fig3 visually checked. Two substrates and different field-facility specimens distinguished. Full supplementary data and model fitting unchecked.\n\n## Claim evidence and conditions\n\n### scwiki-g5-claim-scope-1\n\nThe Jaccarino–Peter effect is compensation of the spin-splitting field experienced by conduction electrons. An exchange contribution opposite to the applied field can reduce Zeeman pair breaking near a finite field. It does not cancel the applied field everywhere in space or remove orbital coupling. A large critical field, a second superconducting pocket or the presence of magnetic ions alone does not establish this mechanism. The original proposal dates to 1962; its identity is verified here, but its full derivation has not been reread.\n\nEvidence: experimental. Sources: source-849f7f4f675464de, source-7d153b141f652513.\n\nConditions: Explicit exchange convention, applied field, temperature, corrected-shift assumptions and probe-specific limits; synthetic examples are not material fits.\n\nVerification scope: Selected primary evidence and independent bounded examples; complete scientific acceptance remains open.\n\n### scwiki-g5-claim-scope-2\n\nMeul and colleagues' 1984 work reports field-induced superconductivity in a Eu–Sn molybdenum chalcogenide system and interprets it through compensation. The original abstract supports that historical connection. Exact composition, numerical field endpoints and complete measurement methods have not been verified here, so they are not promoted to universal material parameters. A classical example cannot supply the missing exchange measurement for a different compound.\n\nEvidence: experimental. Sources: source-d564bee026e788c7.\n\nConditions: Explicit exchange convention, applied field, temperature, corrected-shift assumptions and probe-specific limits; synthetic examples are not material fits.\n\nVerification scope: Selected primary evidence and independent bounded examples; complete scientific acceptance remains open.\n\n### scwiki-g5-claim-mathematical-assumptions-1\n\nChoose the positive direction along the applied field and define the signed effective field as $B_{\\mathrm{eff}}=B_{\\mathrm{ext}}+B_{\\mathrm{ex}}$. Compensation requires $B_{\\mathrm{ex}}\\lt0$ in this convention. In the collinear single-band illustration, spin energies are $E_\\pm=\\pm h$, with $h=g\\mu_B B_{\\mathrm{eff}}/2$ and positive $g$. Their full separation is $2|h|=g\\mu_B|B_{\\mathrm{eff}}|$. A source using another sign for its exchange constant must first be translated into this convention; the sign of a symbol called J is not transferable without its Hamiltonian.\n\nEvidence: theory. Sources: source-849f7f4f675464de, source-7d153b141f652513.\n\nConditions: Explicit exchange convention, applied field, temperature, corrected-shift assumptions and probe-specific limits; synthetic examples are not material fits.\n\nVerification scope: Selected primary evidence and independent bounded examples; complete scientific acceptance remains open.\n\n### scwiki-g5-claim-mathematical-assumptions-2\n\nAn independent synthetic example isolates an inference used in shift measurements. Suppose corrected frequency shifts obey $y=m(B-B_*)$, with nonzero, field-independent slope and a saturated exchange contribution. A fitted line $y=mB+c$ gives $B_*=-c/m$. Four imposed fields, 14.5, 21, 26 and 28 T, recover six noiseless examples with target intercepts of 20, 32 and 40 T and both slope signs. The latter two targets are extrapolations outside this measurement interval. These calculations reproduce the algebra, not published spectra.\n\nEvidence: theory. Sources: source-473d207bc401a7e7.\n\nConditions: Explicit exchange convention, applied field, temperature, corrected-shift assumptions and probe-specific limits; synthetic examples are not material fits.\n\nVerification scope: Selected primary evidence and independent bounded examples; complete scientific acceptance remains open.\n\n### scwiki-g5-claim-mathematical-assumptions-3\n\nA residual constant correction $d$ moves the inferred intercept by $-d/m$. In the synthetic examples, a 0.06 MHz offset shifts it by +2 T for a slope of -0.03 MHz/T, or by -1.2 T for +0.05 MHz/T. A zero slope leaves the intercept unidentifiable. Nine separate spin-energy checks verify the distinction between half splitting and full splitting, including negative effective fields. Neither exercise contains orbital coupling, spin-flip scattering or a gap equation, so neither demonstrates a superconducting transition.\n\nEvidence: theory. Sources: source-473d207bc401a7e7, source-f328f3068f201541.\n\nConditions: Explicit exchange convention, applied field, temperature, corrected-shift assumptions and probe-specific limits; synthetic examples are not material fits.\n\nVerification scope: Selected primary evidence and independent bounded examples; complete scientific acceptance remains open.\n\n### scwiki-g5-claim-experimental-criteria-1\n\nBalicas and colleagues measured four-terminal transport in lambda-(BETS)2FeCl4 with field near the conducting plane. Their phase diagram distinguishes resistive midpoints from resistance below instrumental sensitivity; the broad 18–41 T field-induced region is not uniformly a zero-resistance region. Below 2 K, resistance reaches the experimental zero near 33 T. Tilting introduces a transverse component that suppresses the state. Figure 3's pairing-state curves are theoretical fits, not direct imaging of a modulated order parameter. These results support a compensation interpretation while retaining orbital and measurement limits.\n\nEvidence: experimental. Sources: source-7d153b141f652513.\n\nConditions: Explicit exchange convention, applied field, temperature, corrected-shift assumptions and probe-specific limits; synthetic examples are not material fits.\n\nVerification scope: Selected primary evidence and independent bounded examples; complete scientific acceptance remains open.\n\n### scwiki-g5-claim-experimental-criteria-2\n\nHiraki and colleagues provide a different probe: corrected 77Se NMR shifts in the metallic state at 1.5 K and fields up to 28 T. They infer an exchange-field magnitude of 32 ± 2 T by extrapolating a field-dependent shift. This is not an observed zero crossing at 32 T. Chemical, dipolar and demagnetization corrections enter the analysis; demagnetization dominates their stated uncertainty. The interpretation assumes sufficiently saturated local moments and suitable field-independent electronic response. The transport specimen discussed alongside the NMR came from the same batch, not necessarily the identical crystal.\n\nEvidence: experimental. Sources: source-473d207bc401a7e7.\n\nConditions: Explicit exchange convention, applied field, temperature, corrected-shift assumptions and probe-specific limits; synthetic examples are not material fits.\n\nVerification scope: Selected primary evidence and independent bounded examples; complete scientific acceptance remains open.\n\n### scwiki-g5-claim-experimental-criteria-3\n\nWu and colleagues instead infer an exchange field of -32.7 ± 1.5 T from a 9 T, 5 K angular-shift experiment. Their author manuscript uses a hyperfine calibration partly informed by the nonmagnetic Ga analogue, and explicitly excludes an unknown uncertainty in its axial Knight-shift coefficient. Its predicted value at 33 T is a further model adjustment. Keep the applied field, temperature, inferred exchange field and uncertainty scope separate; the quoted exchange magnitude is not the applied field at which these spectra were taken.\n\nEvidence: experimental. Sources: source-f328f3068f201541.\n\nConditions: Explicit exchange convention, applied field, temperature, corrected-shift assumptions and probe-specific limits; synthetic examples are not material fits.\n\nVerification scope: Selected primary evidence and independent bounded examples; complete scientific acceptance remains open.\n\n### scwiki-g5-claim-experimental-criteria-4\n\nFor a new material, the evidence should connect a measured local-moment response to a signed electronic exchange contribution, then test whether its field and angle dependence account for the superconducting observations. Compare transport with independent magnetic or thermodynamic evidence where available. Different samples, transition criteria, pressure conditions and temperatures must remain identifiable. A numerical similarity between a resistance minimum and an inferred exchange field is supporting evidence, not a replacement for calibration or alternative-mechanism tests.\n\nEvidence: experimental. Sources: source-7d153b141f652513, source-473d207bc401a7e7, source-f328f3068f201541.\n\nConditions: Explicit exchange convention, applied field, temperature, corrected-shift assumptions and probe-specific limits; synthetic examples are not material fits.\n\nVerification scope: Selected primary evidence and independent bounded examples; complete scientific acceptance remains open.\n\n### scwiki-g5-claim-limits-and-disputes-1\n\nThe selected Wu author manuscript has a convention issue requiring further review: the signed angular-difference formula and the subsequent printed numerical input do not match under direct substitution. The final publisher abstract confirms the reported exchange value, but the full final calibration has not been compared. This page therefore attributes the value to the authors and does not claim to reproduce it independently. The discrepancy is an unresolved source-version issue, not evidence that the experimental phenomenon is false. Complete scientific acceptance remains open.\n\nEvidence: experimental. Sources: source-f328f3068f201541.\n\nConditions: Explicit exchange convention, applied field, temperature, corrected-shift assumptions and probe-specific limits; synthetic examples are not material fits.\n\nVerification scope: Selected primary evidence and independent bounded examples; complete scientific acceptance remains open.\n\n### scwiki-g5-claim-limits-and-disputes-2\n\nThe 2026 Eu-rich Sm/Ca/Eu nickelate study reports reentrance and discusses exchange compensation alongside other magnetic physics. Its selected later author version leaves the magnetic order unresolved and includes sample-dependent angular behavior. It does not justify a universal claim of established ferromagnetism or triplet pairing. A separate Nd/Eu nickelate study develops a paramagnetic-compensation interpretation using different material and substrate conditions. Their similarities motivate tests; they do not make the two systems interchangeable or establish one uniquely complete mechanism.\n\nEvidence: experimental. Sources: source-3504ee9027165d0a, source-b57e3b2b5a90705f.\n\nConditions: Explicit exchange convention, applied field, temperature, corrected-shift assumptions and probe-specific limits; synthetic examples are not material fits.\n\nVerification scope: Selected primary evidence and independent bounded examples; complete scientific acceptance remains open.\n\n### scwiki-g5-claim-discovery-implications-1\n\nStore the exchange-field estimate with its sign convention, probe, applied field, temperature, correction model and uncertainty coverage. Record whether compensation was measured directly, extrapolated or assumed in fitting a phase boundary. Separate those records from superconducting transition temperatures. For multiband systems, test whether one effective exchange field is adequate rather than assuming every band has the same coupling. Preserve the independently measured orbital constraints when evaluating candidate compensation windows.\n\nEvidence: experimental. Sources: source-473d207bc401a7e7, source-f328f3068f201541, source-3504ee9027165d0a.\n\nConditions: Explicit exchange convention, applied field, temperature, corrected-shift assumptions and probe-specific limits; synthetic examples are not material fits.\n\nVerification scope: Selected primary evidence and independent bounded examples; complete scientific acceptance remains open.\n\n## Revision and review\n\nArticle ID: scwiki-g5. Revision: 181c58dcf6e6ef6fa7de. Updated: 2026-10-18T16:13:01.109773+00:00.\n\nReview scope: Historical publisher records, selected original organic transport and NMR evidence, inherited scoped nickelate review and independent shift/energy examples.\n\n- Complete scientific acceptance remains open.\n- Wu author calibration sign mismatch and excluded systematic uncertainty remain unresolved; final full-text comparison open.\n- Exchange estimates are attributed inferences, not independent raw-spectrum reproductions.\n- Compensation does not remove orbital pair breaking or alone establish superconductivity.\n\nSource: [G_magnetism_interplay/G5_Jaccarino_Peter_effect.md](https://github.com/JackZH26/jzis-superconductivity/blob/0a7c9d6696804ec26aa12f8eed68b55c9b3c0fcf/G_magnetism_interplay/G5_Jaccarino_Peter_effect.md), commit 0a7c9d6696804ec26aa12f8eed68b55c9b3c0fcf, SHA-256 f7d671b50e5e4f9221acad24e3205b36e6f7e316d52c449e9c66e977cfc8fa5a.\n","wordCount":981}}