Low-dimensional quantum antiferromagnetism in frustrated potassium 3<i>d</i> transition metal (II) phosphates: Insights from experimental and first-principles investigations

Anhydrous phosphate compounds based on 3d transition metal ions can exhibit rich physical behaviors in fundamental condensed matter physics. Herein, we report the structures and low-dimensional quantum magnetism in potassium-based phosphates, KMPO4 (M = Cu, Co), by cooperation of experimental investigations and first-principles density functional theory (DFT) calculations. Magnetic susceptibility measurement performed on KCuPO4 reveals the presence of strong quasi-one-dimensional antiferromagnetic (AFM) behavior with S=12 Cu2+ Heisenberg spin chains. The analysis of heat capacity data verifies the distinct AFM order occurs at TN = 14.1 K obtained from the -susceptibility, while cobalt phosphate KCoPO4 shows no magnetic ordering down to T = 1.9 K. Furthermore, the fairly small ratio of J*/|J| ≈ 3.85 × 10−2, where J/kB (=−141.86 K) is the nearest-neighbor spin-exchange coupling parameter estimated from susceptibility data and J*/kB (≈5.46 K) is the interchain coupling under the mean field approximation, respectively, providing additional evidence that KCuPO4 is almost an ideal one-dimensional AFM compound. Our DFT calculations confirmed that KCuPO4 has a magnetic sublattice in which one-dimensional AFM exchange interactions are weakly coupled ferromagnetic chains. In addition, significant magnetic frustrations are verified in both KCuPO4 and KCoPO4, implying the possibility of a quantum magnetic phase in this phosphate family.