Polaron-mediated anisotropic exchange in 2D magnets

Abstract

Two-dimensional (2D) magnets offer a rich platform for exploring emergent spin phenomena due to their unique and diverse magnetic properties. Beyond intrinsic magnetism, external manipulation$\unicode{x2013}$such as defect engineering, molecular adsorption, or charge doping$\unicode{x2013}$offers powerful routes to control their magnetic behavior. In this work, we demonstrate that localized electron polarons provide an effective means to modulate magnetism in 2D magnets. Using first-principles calculations, we investigate polaron formation in monolayer MnPS$_3$ and compute the resulting changes in magnetic exchange interactions. Our results reveal that polarons can locally break magnetic symmetry and induce anisotropic exchange couplings, highlighting a novel mechanism for tuning magnetic textures. This insight opens promising pathways for designing atomic-scale control of magnetism, with potential impact on spintronic technologies.

Figures (5)

• Figure 1: Convergence of the $J_{1,2}^{yy}$ component of the polaronic system with the penalty parameter $\lambda$.
• Figure 2: (a) Spin-polarized projected DOS of MnPS$_3$ monolayer, showing Mn $d$ states (orange), P $p$ states (purple), and S $p$ states (pink). The upper panel (DOS $>$ 0) represents the spin-up channel, while the lower panel (DOS $<$ 0) corresponds to the spin-down channel. (b) Spin-polarized band structure of the bare, undoped $3\times3\times1$ MnPS$_3$ monolayer and of the polaronic solution. The spin-up and spin-down channels are shown in red and blue, respectively. Note that the two band structures span different energy ranges.
• Figure 3: Crystal lattice of $3\times3\times1$MnPS3 monolayer with a polaron, visualized as the torquoise charge-density cloud corresponding to the in-gap peak in Figure \ref{['Figure1']}. The displacement of Mn atoms induced by the polaron is indicated by blue arrows in the close-up figure. The Mn atoms that were used for the calculation of the nearest-neighbor exchange matrices $J_{ij}$ are labelled. Visualization done using vestamomma2011vesta.
• Figure 4: Polarons in MnPS$_3$ monolayer at different concentrations. (a) one polaron in a $\sqrt{3}\times\sqrt{3}$ supercell, corresponding to an $11.1\%$ concentration; (b) two polarons in the same $\sqrt{3}\times\sqrt{3}$ supercell, yielding a $22.2\%$ concentration; (c) three polarons in the $\sqrt{3}\times\sqrt{3}$ supercell, corresponding to $33.3\%$, and (d) one polaron in a smaller $2\times2$ supercell, corresponding to a $25\%$ concentration.
• Figure A1: Spin-polarized DOS of the doped $3\times3\times1$ MnPS$_3$ monolayer in the delocalized charge configuration. The upper panel displays the majority spin channel (red), while the lower panel corresponds to the minority spin channel (blue).