Upper critical field of an aligned Nax(H3O)zCoO2∙yH2O superconductor from magnetization measurements
Zhi Ren, Chunmu Feng, Zhuan Xu, Minghu Fang, Guanghan Cao
DOI 10.1103/PhysRevB.76.132501 · Physical Review B
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Abstract
We present magnetization measurements for the upper critical field Hc2 on aligned Nax(H3O)zCoO2∙yH2O superconductors with magnetic field parallel to CoO2 layers. The temperature-dependent part of the normal-state magnetization M(H,T) can be well scaled with Brillouin function, suggesting the existence of impurity moments. By subtracting the contribution of the magnetic impurity moments, a well defined onset of superconducting diamagnetism allows the in-field superconducting transition temperature Tc(H) to be accurately determined. No superconducting transition was observed down to 1.9K under an applied field of 8T. The result suggests that the Hc2‖ab(0) value is just within the Pauli paramagnetic limit, supporting spin-singlet superconductivity in the cobalt oxyhydrate superconductor. Additionally, the upward curvature near Tc in the Hc2‖ab−T phase diagram was confirmed to be intrinsic. Possible origin of the anomaly was discussed.
Source-reported materials — not catalogue approval
| Formula | Reported Tc (K) | Pressure (GPa) | Type |
|---|---|---|---|
| Na0.33(H3O)0.02CoO2*1.4H2O Archive — visibility unverified Source-occurrence policy only; no material identity or catalogue acceptance is inferred from the formula. | 4.5 | Pressure not reported | onset |
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