Field-dependent diamagnetic transition in magnetic superconductor $Sm_{1.85} Ce_{0.15} Cu O_{4-y}$

TL;DR

This study measures the magnetic penetration depth in a superconducting compound, revealing a field-dependent spin freezing transition that enhances superfluid density at low temperatures.

Contribution

It reports the discovery of a field-dependent diamagnetic transition in a magnetic superconductor, linking it to a spin freezing process affecting superfluid density.

Findings

Diamagnetic screening sharply increases below a temperature $T^{ullet}(H)$.

$T^{ullet}$ varies with magnetic field when aligned along the c-axis.

Spin freezing transition enhances superfluid density.

Abstract

The magnetic penetration depth of single crystal $\rm{Sm_{1.85}Ce_{0.15}CuO_{4-y}}$ was measured down to 0.4 K in dc fields up to 7 kOe. For insulating $\rm{Sm_2CuO_4}$, Sm$^{3+}$ spins order at the N\'{e}el temperature, $T_N = 6$ K, independent of the applied field. Superconducting $\rm{Sm_{1.85}Ce_{0.15}CuO_{4-y}}$ ($T_c \approx 23$ K) shows a sharp increase in diamagnetic screening below $T^{\ast}(H)$ which varied from 4.0 K ($H = 0$) to 0.5 K ($H =$ 7 kOe) for a field along the c-axis. If the field was aligned parallel to the conducting planes, $T^{\ast}$ remained unchanged. The unusual field dependence of $T^{\ast}$ indicates a spin freezing transition that dramatically increases the superfluid density.