Synthesis and magnetic properties of two fluorophosphates K2Mn(PO3F)F3 and Na2Mn(HPO4)F3 with a S = 2 uniform spin chain structure

Abstract

Two fluorophosphates K₂Mn(PO₃F)F₃ (1) and Na₂Mn(HPO₄)F₃ (2) were synthesized through a hydrothermal method. It was found that 1 and 2 crystallize in the monoclinic space group of P2₁/c and P2₁/m, respectively, both exhibiting a uniform chain structure formed by MnO₂F₄ octahedra with corner-sharing F atoms along the b-axis. Magnetic and heat capacity measurements confirm that both compounds possess a short-range magnetic ordering at ∼50 K and a long-range antiferromagnetic ordering below 15 K, showing their closing intra-chain exchange interactions, where the magnetic entropy change for such antiferromagnetic ordering can be estimated to be 0.19 J mol⁻¹ K⁻¹ for 1 and 0.29 J mol⁻¹ K⁻¹ for 2, respectively.