Thermal cycling induced alteration of the stacking order and spin-flip in the room temperature van der Waals magnet <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:mrow><mml:msub><mml:mi>Fe</mml:mi><mml:mn>5</mml:mn></mml:msub><mml:msub><mml:mi>GeTe</mml:mi><mml:mn>2</mml:mn></mml:msub></mml:mrow></mml:math>
Xiang Chen, Wei Tian, Yu He, Hongrui Zhang, Tyler Werner, Saul H. Lapidus, Jacob P. C. Ruff, R. Ramesh, R. J. Birgeneau
Abstract
The magnetic properties of the quasi-two-dimensional van der Waals magnet ${\mathrm{Fe}}_{5\ensuremath{-}\ensuremath{\delta}}{\mathrm{GeTe}}_{2}$ (F5GT), which has a high ferromagnetic ordering temperature ${T}_{\text{C}}\ensuremath{\sim}315$ K, remain to be better understood. It has been demonstrated that the magnetization of F5GT is sensitive to both the Fe deficiency $\ensuremath{\delta}$ and the thermal-cycling history. Here, we investigate the structural and magnetic properties of F5GT single crystals with a minimal Fe deficiency $(|\ensuremath{\delta}|\ensuremath{\le}0.1)$, utilizing combined x-ray and neutron scattering techniques. Our study reveals that the quenched F5GT single crystals experience an irreversible, first-order transition at ${T}_{\text{S}}\ensuremath{\sim}110$ K upon first cooling, where the stacking order partly or entirely converts from ABC-stacking order to AA-stacking order. Importantly, the magnetic properties, including the magnetic moment direction and the enhanced ${T}_{\text{C}}$ after the thermal cycling, are intimately related to the alteration of the stacking order. Our work highlights the significant influence of the lattice symmetry to the magnetism in F5GT.