Spin reorientation in FeCrAs revealed by single-crystal neutron diffraction

TL;DR

This study reveals the temperature-dependent spin reorientation in FeCrAs, showing a spiral antiferromagnetic order with complex magnetic behavior linked to frustration and itinerant magnetism, explaining previously unexplained magnetic transitions.

Contribution

The paper uncovers the detailed magnetic structure and spin reorientation in FeCrAs using neutron diffraction, highlighting the interplay of frustration and itinerant magnetism in its magnetic phases.

Findings

Cr moments show in-plane spiral antiferromagnetic order

Cr moments cant out of plane with increasing temperature

Spin reorientation explains magnetic susceptibility features

Abstract

The magnetic structure of the "nonmetallic metal" FeCrAs, a compound with the characters of both metals and insulators, was examined as a function of temperature using single-crystal neutron diffraction. The magnetic propagation vector was found to be $\mathit{k}$ = (1/3, 1/3, 0), and the magnetic reflections disppeared above $\mathit{T_{N}}$ = 116(1) K. In the ground state, the Cr sublattice shows an in-plane spiral antiferromagnetic order. The moment sizes of the Cr ions were found to be small, due to strong magnetic frustration in the distorted Kagome lattice or the itinerant nature of the Cr magnetism, and vary between 0.8 and 1.4 $\mu_{B}$ on different sites as expected for a spin-density-wave (SDW) type order. The upper limit of the moment on the Fe sublattice is estimated to be less than 0.1 $\mu_{B}$. With increasing temperature up to 95 K, the Cr moments cant out of the $\mathit{ab}$ plane gradually, with the in-plane components being suppressed and the out-of-plane components increasing in contrast. This spin-reorientation of Cr moments can explain the dip in the $\mathit{c}$-direction magnetic susceptibility and the kink in the magnetic order parameter at $\mathit{T_{O}}$ ~ 100 K, a second magnetic transition which was unexplained before. We have also discussed the similarity between FeCrAs and the model itinerant magnet Cr, which exhibits spin-flip transitions and SDW-type antiferromagnetism.