High temperature phase transition of the magnetoelectric double perovskite Sr2NiMoO6 by neutron diffraction

The magnetic ferroelectric double perovskite Sr2NiMoO6 has been characterised using neutron powder diffraction (NPD) data and magnetic susceptibility measurements. High temperature NPD data indicate that the material undergoes a continuous structural phase transition from tetragonal (I4/m) to cubic (Fm  3¯m) at approximately 550 K. The transition is linked to the level of rotation of the NiO6 and MoO6 octahedra, which form perfectly segregated sub-lattices in the material. The reduction in symmetry at 550 K is linked to the onset of a spontaneous dipole in the material allowing the structural perturbation to be described as an improper ferroelectric phase transition. The appearance of low angle reflections in the 20 K dataset indicates the presence of an antiferromagnetic ordered ground state. The magnetic moment was refined to 1.88(8) μB confirming that the magnetism originates from the Ni2+ (S = 1) ions.