Strain-tunable ferromagnetic to antiferromagnetic and half-metallic to ferroelectric phase transitions in a 2D bimetallic oxyhalide

Abstract

The coexistence and tunability of ferroic orders in two-dimensional materials hold great promise for next-generation spintronic and memory devices. Here, based on first-principles calculations, we demonstrate that the interplay of chemical substitution and strain engineering enables controlled phase transitions among ferromagnetic, antiferromagnetic, half-metallic, and ferroelectric states in a two-dimensional bimetallic oxyhalide monolayer NbMnO2Cl4. The pristine NbMnO2Cl4 monolayer exhibits intrinsic half-metallic ferromagnetism, with a Curie temperature of 285 K and magnetic anisotropy energy of 225 μeV per Mn atom. The compressive biaxial strain triggers a sequential transition from half-metallic ferromagnetism to ferroelectric–ferromagnetic and subsequently to ferroelectric–antiferromagnetic states. Conversely, tensile biaxial strain drives a direct transition from half-metallic ferromagnetism to a ferroelectric–antiferromagnetic phase. Spin–lattice coupling plays a crucial role in these phase transitions. Moreover, the Curie temperature increases to 540 K at a tensile strain of 6%, and the magnetic anisotropy energy reaches 670 μeV per Mn atom at a compressive strain of −8%. These findings offer an approach for tailoring multiple ferroic orders in two-dimensional materials through the synergistic effects of chemical doping and mechanical strain.