Jaione Escobal, José L. Mesa, José L. Pizarro, Luis Lezama, Roger Olazcuaga and Teófilo Rojo
Ba(MnPO4)2·H2O has been prepared by hydrothermal synthesis and characterized by spectroscopic and magnetic techniques. Its crystal structure has been solved from X-ray powder diffraction data by using direct methods and refined with the Rietveld method. The compound crystallizes in the monoclinic system in the C2 space group with unit cell parameters, a = 9.457(1), b = 4.984(1), c = 8.346(1) Å and β = 92.07(1)°. The structure consists of a two-dimensional network of MnO6 octahedra, linked by phosphate anions and water molecules, which form chains along the |010| direction. The luminescence properties of Mn(II) in the compound are studied and the values of Dq and Racah parameters B and C have been calculated. The EPR spectra recorded on a polycrystalline sample at different temperatures show isotropic signals with g-values of 2.0. The intensity of the EPR signals increases with decreasing temperature down to 45 K and at lower temperatures rapidly decreases. Magnetic measurements show the presence of antiferromagnetic interactions. An analysis of the magnetic behaviour was carried out considering a theoretical model for antiferromagnetic chains with spin S = 5/2. Similar values for the J-exchange parameter inside the chains (J/k = –2.0 K) and for the J′-exchange parameter between neighbouring chains (zJ′/k = –2.0 K) are observed. These results suggest that the compound can be considered as a non-regular two-dimensional magnetic system.