Magnetic order in 2D antiferromagnets revealed by spontaneous anisotropic magnetostriction.

The temperature dependent order parameter provides important information on the nature of magnetism. Using traditional methods to study this parameter in two-dimensional (2D) magnets remains difficult, however, particularly for insulating antiferromagnetic (AF) compounds. Here, we show that its temperature dependence in AF MPS₃ (M(II) = Fe, Co, Ni) can be probed via the anisotropy in the resonance frequency of rectangular membranes, mediated by a combination of anisotropic magnetostriction and spontaneous staggered magnetization. Density functional calculations followed by a derived orbital-resolved magnetic exchange analysis confirm and unravel the microscopic origin of this magnetization-induced anisotropic strain. We further show that the temperature and thickness dependent order parameter allows to deduce the material's critical exponents characterising magnetic order. Nanomechanical sensing of magnetic order thus provides a future platform to investigate 2D magnetism down to the single-layer limit. Van der Waals antiferromagnets offer a unique platform for studying magnetism in reduced dimensions, however, the low dimensionality, combined with lack of net magnetization, renders investigation challenging with conventional experimental probes. Here, Houmes et al show how van der Waals antiferromagnets can be investigated via the resonances of a vibrating rectangular membranes of this material. [ABSTRACT FROM AUTHOR]