Magnetic Properties of the Ordered Double Perovskite Sr₂MnTeO₆

Abstract

Abstract The ordered double perovskite Sr 2 MnTeO 6 was prepared by the freeze‐drying method. The nuclear and magnetic structures were determined by both X‐ray and neutron (D2B and D1B) powder diffraction. A distorted, double perovskite structure type described by the monoclinic P 12 1 / n 1 space group is observed at room temperature and down to 4 K. The room temperature EPR spectrum shows an isotropic signal centered at a g value of 1.998 indicating that manganese ions are in the +2 oxidation state. At low temperature the EPR signal broadens as the exchange and dipolar interactions between Mn 2+ cations increase. Below 25 K no signal is observed, indicating that the sample is magnetically ordered. The dc magnetic susceptibility shows the existence of antiferromagnetic interactions with an ordering temperature around 20 K. A sharp λ‐type anomaly observed at 19 K in the specific heat curve and refinement of low‐temperature neutron diffraction data confirm the presence of a three‐dimensional, antiferromagnetic ordered structure with an ordering temperature of ca. 23 K. The propagation vector of the magnetic structure is k = [0,0,0], yielding a type I antiferromagnetic ordering between Mn 2+ ( S = 5 / 2 ) cations. At 2 K, each manganese ion is antiferromagnetically aligned to 8 out of 12 nearest‐neighbors at an approximate distance of 5.6 Å. This magnetic structure can be viewed as being composed of ferromagnetic arrangement of Mn 2+ moments in the ab plane, coupled antiferromagnetically along the c axis. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2006)