Strain-tuned magnetoelectric properties of monolayer <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:msub> <mml:mi>NiX</mml:mi> <mml:mn>2</mml:mn> </mml:msub> </mml:math> (X = I, Br): A first-principles analysis

Using ab initio methodology, we reveal a strain\penalty1000-\hskip0ptmediated approach to precisely tune the magnetoelectric coupling and spin-driven emergent polarization of ${\mathrm{NiX}}_{2}$ (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: ($\text{i}$) direct modification of the magnetoelectric tensor components, and ($\text{ii}$) tuning of the characteristic propagation vectors of a spin texture. This dual mechanism enables rather precise control over the magnitude of the spin\penalty1000-\hskip0ptinduced electric polarization of these materials. With respect to the achievable magnitude of the electric polarization, we demonstrate the critical role of third nearest\penalty1000-\hskip0ptneighbor spin\penalty1000-\hskip0ptpair 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.