Lattice-mismatch-induced granularity in CoPt-NbN and NbN-CoPt superconductor-ferromagnet heterostructures: Effect of strain
R. K. Rakshit, S. K. Bose, R. Sharma, N. K. Pandey, R. C. Budhani
DOI 10.1103/PhysRevB.77.094505 · Physical Review B
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Abstract
The effect of strain due to lattice mismatch and of ferromagnetic exchange field on superconductivity (SC) in NbN-CoPt bilayers is investigated. Two different bilayer systems with reversed deposition sequence are grown on MgO (001) single crystals. While robust superconductivity with high critical temperature (Tc≈15.3K) and narrow transition width (ΔTc≈0.4K) is seen in two types of CoPt−NbN∕MgO heterostructures where the magnetic anisotropy of CoPt is in plane in one case and out of plane in the other, the NbN−CoPt∕MgO system shows markedly suppressed SC response. The reduced SC order parameter of this system, which manifests itself in Tc, temperature dependence of critical current density Jc(T), and angular (ϕ) variation of flux-flow resistivity ρf, is shown to be a signature of the structure of NbN film and not a result of the exchange field of CoPt. The ρf (H,T,ϕ) data further suggest that the domain walls in the CoPt film are of the Néel type and hence do not cause any flux in the superconducting layer. A small but distinct increase in the low-field critical current of the CoPt-NbN couple is seen when the magnetic layer has perpendicular anisotropy.
Source-reported materials — not catalogue approval
| Formula | Reported Tc (K) | Pressure (GPa) | Type |
|---|---|---|---|
| NbN Archive — visibility unverified Source-occurrence policy only; no material identity or catalogue acceptance is inferred from the formula. | 15.5 | Pressure not reported | onset |
| NbN Archive — visibility unverified Source-occurrence policy only; no material identity or catalogue acceptance is inferred from the formula. | 15.5 | Pressure not reported | onset |
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