Tuning Magnetic Order and Spin-Exciton Interactions in MnPSe3 via Cu Substitution

Abstract

We report a comprehensive investigation of Cu-substituted MnPSe₃ [Mn_1-xCu_2xPSe₃ (x = 0 -0.2)], a layered van der Waals magnetic semiconductor, revealing a unique interplay between chemical substitution, magnetism, and excitonic behavior. Structural analyses demonstrate that Cu(I) ions substitute Mn(II) at distinct crystallographic sites, producing anisotropic lattice expansion. With increasing Cu content, magnetic susceptibility measurements show a systematic suppression of antiferromagnetic order and a transition to a paramagnetic state beyond x ≥ 0.15. Concurrently, thermal conductivity decreases due to enhanced phonon scattering. Photoluminescence spectroscopy uncovers three sub-bandgap excitons, two of which show pronounced redshifts as a function of temperature, indicating strong spin-exciton coupling. This work establishes chemical substitution as a powerful tool to tune magnetism and spin-exciton interactions in 2D materials, opening new design strategies for spintronic and quantum optoelectronic platforms.