Effect of magnetic order on the superfluid response of single-crystal ErNi$_{2}$B$_{2}$C: A penetration depth study

TL;DR

This study investigates how magnetic ordering affects the superfluid response in ErNi₂B₂C single crystals by measuring the magnetic penetration depth down to 0.1 K, revealing subtle features linked to magnetic transitions.

Contribution

It provides detailed measurements of the superfluid density across magnetic transitions, elucidating the interplay between magnetism and superconductivity in ErNi₂B₂C.

Findings

Antiferromagnetic order slightly depresses superconductivity at 6 K.

Weak ferromagnetic component at 2.3 K shows minimal impact on superfluid density.

Superfluid density decreases slightly near 2.3 K, indicating limited bulk ferromagnetism.

Abstract

We report measurements of the in-plane magnetic penetration depth $\Delta \lambda $(T) in single crystals of ErNi$_{2}$B$_{2}$C down to $\sim$0.1 K using a tunnel-diode based, self-inductive technique at 21 MHz. We observe four features: (1) a slight dip in $\Delta \lambda $(T) at the N$\acute{e}$el temperature $T_{N}$ = 6.0 K, (2) a peak at $T_{WFM}$ = 2.3 K, where a weak ferromagnetic component sets in, (3) another maximum at 0.45 K, and (4) a final broad drop down to 0.1 K. Converting to superfluid density $\rho_{s}$, we see that the antiferromagnetic order at 6 K only slightly depresses superconductivity. We seek to explain some of the above features in the context of antiferromagnetic superconductors, where competition between the antiferromagnetic molecular field and spin fluctuation scattering determines increased or decreased pairbreaking. Superfluid density data show only a slight decrease in pair density in the vicinity of the 2.3 K feature, thus supporting other evidences against bulk ferromagnetism in this temperature range.