Magnetic structure of EuCd$_2$Sb$_2$ single-crystal thin-film

TL;DR

This study combines experimental and theoretical methods to elucidate the magnetic structure of EuCd$_2$Sb$_2$ thin films, revealing interlayer antiferromagnetic order and surface ferromagnetic effects due to oxidation.

Contribution

It provides new insights into the magnetic ordering in EuCd$_2$Sb$_2$ thin films, including the coexistence of antiferromagnetic bulk order and ferromagnetic surface layers, supported by Monte Carlo simulations.

Findings

Sharp magnetic peak indicating interlayer antiferromagnetism below 7.2 K.

Diffuse magnetic signal above T_N suggesting surface ferromagnetism.

Monte Carlo simulations explain surface ferromagnetism due to oxidation.

Abstract

We investigate the magnetic order in single crystalline EuCd$_2$Sb$_2$ thin films using a combined theoretical and experimental approach. Resonant elastic x-ray scattering experiments reveal a sharp magnetic peak at $q = (0, 0, \frac{1}{2})$ below $T_N = 7.2$ K, indicative of interlayer antiferromagnetic ordering. Additionally, we observe a weak diffuse magnetic signal centered at $q = (0, 0, 1)$ that persists above $T_N$, up to $T_C \sim 11$ K. Our Monte-Carlo simulations of a classical spin model approximation of the Eu magnetic sublattice demonstrate that the diffuse signal can arise from ferromagnetic coupling in the top few layers due to surface oxidation. On the other hand, the bulk of the sample exhibits antiferromagnetic coupling between layers. Finally, our fit of the model parameters to the magnetic ordering temperatures, shed light on the exchange couplings that are key in stabilizing the observed composite magnetic order.