Site-Selective Electron Doping and Emerging Ferrimagnetism in K-Intercalated Layered CoPS3 without Metallization

Abstract

Intercalation of layered van der Waals (vdW) materials serves as a powerful approach to modify the physical, electronic, and magnetic properties of parent bulk lattices. Here, we present a comprehensive scanning tunneling microscopy, soft X-ray synchrotron photoelectron spectroscopy, and density functional theory (DFT) study of potassium (K) intercalation within bulk CoPS3 layered crystals. Intercalation of K induces a structural transformation from ABC to AAA stacking, accompanied by a prominent lattice expansion along the c-axis (≈6.4 Å to ≈8.3 Å). Remarkably, resonant photoemission and core-level spectroscopy combined with spin-polarized DFT calculations reveal that the substantial charge transfer from K is site-selective in the lattice. The donated electrons populate a single Co sublattice (Co1), driving its spectral signature toward a lower-valent configuration, while the neighboring sublattice (Co2) remains close to its original Co2+ charge state. This selective local correlation modifies the underlying magnetic exchange interaction, shifting the pristine antiferromagnetic ground state toward a ferri/ferromagnetic phase. Crucially, this selective population preserves the semiconducting nature of the crystal, yielding a gapped electronic structure in the K@CoPS3 intercalation compound (1.06 eV) rather than inducing conventional rigid-band metallization frequently observed in surface-doped systems. This work offers an alternative degree of freedom for engineering spin states and localized interactions in low-dimensional thiophosphates, with direct implications for the design of future spintronic devices, smart sensors, and targeted catalytic platforms.