High-Temperature Intrinsic Two-Dimensional-XY Ferromagnetism and Strong Magnetoelastic Coupling in Tetragonal Monolayer MnGe

The discovery of two-dimensional (2D) materials with novel magnetism is a compelling problem of condensed material physics and materials science but is still a challenge. Here, we report first-principles calculations that show evidence of an extraordinary combination of high-temperature intrinsic ferromagnetism and strong magnetoelastic coupling driven by strain-induced in-plane magnetic anisotropy in a new 2D tetragonal nanosheet MnGe (t-MnGe). Our study unveils that t-MnGe is ferroelastic with a moderate activation barrier (43 meV/atom), indicating that both the ferroelastic switching and controllable anisotropy in 2D ferroelastic t-MnGe are experimentally accessible. Specifically, this novel 2D material is predicated to be an intrinsic 2D-XY ferromagnet with a Berezinskii–Kosterlitz–Thouless transition temperature much beyond 300 K and robust easy-plane character against elastic strain. Our results also identify that the free-standing t-MnGe nanosheet is sufficiently stable and can be exfoliated from its bulk counterparts with a van der Waals layered structure in experiment. These advantages offer a highly versatile and promising system for exploring exotic magnetic phenomena and better information technology above room temperature.