Inhomogeneous Magnet NaMnIII[BP2O7(OH)3]: Ferromagnetic Clusters Inserted in a Metamagnetic Matrix

Abstract

AbstractNaMnIII[BP2O7(OH)3] (1) has been hydrothermally synthesized and characterized by single‐crystal X‐ray diffraction. The manganese(III) cations are coordinated in a tetragonal‐elongated octahedral environment, indicating the possible large magnetic anisotropy. The MnO6 octahedra are interconnected by BO4/PO4 groups, forming a 3D triclinic net of MnIII backbone. Detailed dc and ac magnetic measurements have been conducted, and a preliminary H–T phase diagram is deduced accordingly. Compound 1 adopts an unusual magnetic inhomogeneous model, consisting of ferromagnetic clusters and a metamagnetic background: At the paramagnetic temperature region, the Curie–Weiss fit shows that the manganese atoms are all in the high spin state (S = 2), and the predominant interaction is ferromagnetic. An antiferromagnetic ground state forms at approximately 10 K, the isothermal magnetizations between 6.5 and 10 K show the typical metamagnetism. At approximately 6.5 K, a short‐range ordering of the ferromagnetic cluster occurs. Below 3.5 K, the ferromagnetic clusters tend to be frozen at low external field, and the inhomogeneous magnetism can be clearly indicated by the isothermal magnetizations below 3 K. This unusual magnetism cannot be understood by the popular mechanism in doped manganese perovskites, which are well known to be magnetically inhomogeneous because of the mixed valence of manganese. In compound 1, one of the possible reasons for this unusual behaviour is the competition between magnetic superexchange interactions and the large magnetic anisotropy of MnIII.(© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2009)