Strain-tuned magnetoelectric properties of monolayer NiX 2 (X = I, Br): A first-principles analysis

Using ab initio methodology, we reveal a strain1000-0ptmediated approach to precisely tune the magnetoelectric coupling and spin-driven emergent polarization of NiX₂ (X = I, Br) monolayers. In the absence of strain, these systems spontaneously stabilize noncollinear spin states that break the inversion symmetry, inducing a ferroelectric polarization in the plane of the material. We show that biaxial and uniaxial strains broadly modulate the magnetoelectric response in these materials through two distinct mechanisms: (i) direct modification of the magnetoelectric tensor components, and (ii) tuning of the characteristic propagation vectors of a spin texture. This dual mechanism enables rather precise control over the magnitude of the spin1000-0ptinduced electric polarization of these materials. With respect to the achievable magnitude of the electric polarization, we demonstrate the critical role of third nearest1000-0ptneighbor spin1000-0ptpair contributions, which can increase under strain to levels that compete with or even exceed the polarization driven by first nearest-neighbor effects. These findings offer important insights into low-dimensional piezomagnetoelectricity and expand the possibilities for designing multifunctional 2D straintronic devices.