First-principles study of strain-controlled magnetic properties in MPX3 (M = Mn, Ni; X = S, Se) monolayers

Two-dimensional materials MPX₃ (M = 3d transition metals; X = chalcogens) monolayers have attracted significant attention due to their rich magnetic phase diagrams and potential for various applications. The complex competition among different magnetic exchange interactions places NiPX₃ (X = S, Se) monolayers at a critical region between the zigzag-antiferromagnetic (AFM) and Néel-AFM phases, implying that their magnetic properties can be modulated by multiple fields. In this study, we systematically investigated the magnetic properties of NiPX₃ monolayers by employing first-principles calculations, exploring the modulation of magnetic behaviour under internal (element substitution) and external strains (biaxial/uniaxial strain). Our results demonstrate that both magnetic anisotropy and the magneto-optical Schäfer-Hubert (SH) effect are strongly influenced by strain. Specifically, strain can induce a flip of the magnetic easy axis from in-plane to out-of-plane and significantly enhance the magneto-optical SH effect. For instance, under −6 % biaxial compressive strain, the SH rotation angle peak of the NiPSe₃ monolayer increases from −0.62° in NiPS₃ to −1.71°. The distortion of the trigonal anti-prismatic crystal field and the breaking of the three-fold rotational symmetry are identified as the key physical mechanisms responsible for the strain-induced tuning of magnetic anisotropy and the magneto-optical SH effect. Our work provides a theoretical framework and a material design approach for achieving multi-parameter functional modulation in ultrathin spintronic devices.