Synthesis, structure and magnetic behaviors of a new fluorophosphate PbCuPO4F

Abstract A new fluorophosphate PbCuPO4F was obtained by a hydrothermal method, which is found to crystallize in the monoclinic system with a P21/c space group, exhibiting a tunnel structure built by distorted CuO4F square-pyramids and PO4 tetrahedra. Magnetic measurements show that this compound possesses a short-range magnetic order at ∼7.9 K without any antiferromagnetic transitions down to 2 K, indicating a singlet ground state. The fit by a modified spin-dimer model indicates intradimer interaction J/kB = 12.2 K and interdimer interaction J’/kB = 3.5 K in the system, while the critical field for the spin gap between the singlet ground state (S = 0) and the excited triplet states (S = 1) is observed at Hc = ∼4.7 T. Although PbCuPO4F and BaCuPO4F have a similar tunnels structure, their magnetic behaviors are remarkably different. This may be due to a slight change of interaction exchange in PbCuPO4F, leading to a coupled spin-dimer of Cu–O–P–O–Cu pathway in the 4-column tunnels. Also, solid-state UV–vis diffuse reflectance spectra show that PbCuPO4F has wide optical band gap of 3.42 eV.