Synthesis and magnetic properties of two fluorophosphates K 2 Mn(PO 3 F)F 3 and Na 2 Mn(HPO 4 )F 3 with a S = 2 uniform spin chain structure

Two fluorophosphates K 2 Mn(PO 3 F)F 3 (1) and Na 2 Mn(HPO 4 )F 3 (2) were synthesized through a hydrothermal method. It was found that 1 and 2 crystallize in the monoclinic space group of P 2 1 / c and P 2 1 / m , respectively, both exhibiting a uniform chain structure formed by MnO 2 F 4 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.