Magnetic-field-induced ab-plane rotation of the Eu magnetic moments in trigonal EuMg2Bi2 and EuMg2Sb2 single crystals below their Neel temperatures

TL;DR

This study investigates the magnetic field-induced reorientation of Eu magnetic moments in EuMg2Bi2 and EuMg2Sb2, revealing a new spin-reorientation transition and modeling their magnetic anisotropies.

Contribution

It reports the discovery of a low-field spin-reorientation transition and provides a theoretical model for magnetic behavior in EuMg2Bi2 and EuMg2Sb2.

Findings

Identification of a new spin-reorientation transition at low magnetic fields.

EuMg2Bi2 exhibits a larger ab-plane anisotropy than EuMg2Sb2.

Magnetic moments align with the field at high fields, with specific critical fields identified.

Abstract

The thermodynamic and electronic-transport properties of trigonal EuMg2Bi2 in ab-plane magnetic fields Hx and the A-type antiferromagnetic structure have recently been reported. At a temperature of 1.8 K < TN, the Eu magnetic moments with spin S = 7/2 remain locked in the ab plane up to and above the ab-plane critical field Hxc = 27.5 kOe at which the Eu moments become parallel to Hx. Here additional measurements at low fields are reported that reveal a new spin-reorientation transition at a field Hc1 = 465 Oe where the Eu moments remain in the ab plane but become perpendicular to Hx. At higher fields, the moments cant towards the field resulting in M proportional to Hx up to Hxc. Similar results are reported from measurements of the magnetic properties of EuMg2Sb2 single crystals, where Hc1 = 220 Oe is found. Theory is formulated that models the low-field magnetic behavior of both materials, and the associated anisotropies are calculated. The ab-plane trigonal anisotropy in EuMg2Sb2 is found to be significantly smaller than in EuMg2Bi2.