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arXiv · 2203.09049

Anticollinear order and degeneracy lifting in square lattice antiferromagnet LaSrCrO4

Jing Zhou·Guy Quirion·Jeffrey A. Quilliam·Huibo Cao·Feng Ye·Matthew B. Stone·Qing Huang·Haidong Zhou·Jinguang Cheng·Xiaojian Bai·Martin Mourigal·Yuan Wan·Zhiling Dun
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Abstract

We report the static and dynamic magnetic properties of LaSrCrO$_4$, a seemingly canonical spin-3/2 square-lattice antiferromagnet that exhibits frustration between magnetic layers -- owing to their AB stacking -- and offers a rare testbed to investigate accidental-degeneracy lifting in magnetism. Neutron diffraction experiments on single-crystal samples uncover a remarkable anticollinear magnetic order below $T_N$ = 170 K characterized by a N\'eel arrangement of the spins within each layer and an orthogonal arrangement between adjacent layers. To understand the origin of this unusual magnetic structure, we analyze the spin-wave excitation spectrum by means of inelastic neutron scattering and bulk measurements. A spectral gap of 0.5 meV, along with a spin-flop transition at 3.2\, T, reflect the energy scale associated with the degeneracy-lifting. A minimal model to explain these observations requires both a positive biquadratic interlayer exchange and dipolar interactions, both of which are on the order of 10$^{-4}$ meV, only a few parts per million of the dominant exchange interaction $J_1 \approx 11$ meV. These results provide direct evidence for the selection of a non-collinear magnetic structure by the combined effect of two distinct degeneracy lifting interactions.

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Jing Zhou, Guy Quirion, Jeffrey A. Quilliam, Huibo Cao, Feng Ye, Matthew B. Stone, Qing Huang, Haidong Zhou, Jinguang Cheng, Xiaojian Bai, Martin Mourigal, Yuan Wan, Zhiling Dun. 2022-03-17. Anticollinear order and degeneracy lifting in square lattice antiferromagnet LaSrCrO4. https://doi.org/10.1103/physrevb.105.l180411

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