High-pressure synthesis and study of the crystal and magnetic structure of the distorted SeNiO3 and SeMnO3 perovskites

Abstract

We describe the preparation of SeMO₃ (M = Ni, Mn) under high pressure conditions (3.5 GPa), starting from reactive H₂SeO₃ and MO mixtures, contained in sealed gold capsules under the reaction conditions 850 °C for 1 h. The polycrystalline samples have been studied by neutron powder diffraction (NPD) data and magnetization measurements. SeMO₃ (M = Ni, Mn) are orthorhombically distorted perovskites (space group Pnma). Below T_N ≈ 104 K (M = Ni) and T_N ≈ 53.5 K (M = Mn) these oxides experience an antiferromagnetic ordering, as demonstrated by susceptibility and NPD measurements. The magnetic reflections observed in the neutron patterns can be indexed with a propagation vector k = 0. Both compounds present the same magnetic structure, which is given by the basis vector (0, 0, A_z). It can be described as antiferromagnetic (010) layers of magnetic moments lying along the c direction, which are antiferromagnetically coupled along the b direction. For the Ni²⁺ ions, the ordered magnetic moment at T = 2.3 K is 2.11(3) µ_B, whereas for Mn²⁺ at T = 2.6 K, |m| = 4.64(2) µ_B, consistent with the electronic configurations t⁶_2ge²_g (Ni²⁺) and t³_2ge²_g (Mn²⁺).