Synthesis, Crystal Structure, and Magnetic Characterization on a Frustrated S = 1 Magnet KNi(PO3)3

KNi(PO 3 ) 3 was successfully synthesized by solid-state method and the magnetic properties were characterized. The crystal structure of KNi(PO 3 ) 3 belongs to trigonal crystal system with space group R 3, where Ni 2+ ions form the distorted honeycomb-lattice within the ab-plane stacking in the “ABAB” type fashion along the c -axis. Magnetization measurements reveal the presence of antiferromagnetic (AFM) interaction with Curie Weiss (CW) temperature θ CW  =  − 12.905 K but without long-range magnetic order down to 2 K. Notably, the CW fitted effective moment µ eff  = 3.35µ B and saturated magnetization M S  = 2 μ B /Ni 2+ at 2 K support KNi(PO 3 ) 3 as an S  = 1 spin system. Intriguingly, the zero-field specific heat exhibits a broad peak maximized at ~ 2.5 K indicating the onset of short-range spin correlation between Ni 2+ ions, while the integrated magnetic entropy ( S mag ) is close to the expected Rln3 for S  = 1 system, indicative of large spin fluctuation below 2 K driven by spin frustration.