Ordered double perovskites have the chemical formula A2BB'O6, where A is a rare earth or alkaline, and B and B' are transition metals or, in some cases, post-transition and non-metals. Within the structure, the B and B′ cations generally form either a rock-salt or layered type superstructure. Some double perovskites show colossal magnetoresistance (CMR), which enables them to dramatically change their electrical resistance in the presence of a magnetic field, due to the half-metallic nature of their electronic structures.
This study introduces the double perovskite Tl2NiMnO6. As the B (Ni2+) and B’ (Mn4+) cations have similar radii, they can partially occupy the sites of the other, depending on the temperature and pressure used during synthesis. This work is dedicated to investigating the crystal, magnetic and electronic structures by a combination of neutron diffraction experiments on WISH, magnetic, heat capacity and magneto-transport measurements, and density functional theory calculations.
The group discovered that the extent of cation ordering has a large impact on the magnetic properties of the material. By reducing the degree of ordering of the cations from 70% to 31%, the long range ferromagnetic order is suppressed, resulting in short range spin correlations and glass-like behaviour. The ordered sample exhibits a low-field CMR: the first example of a ferromagnetic insulating double perovskite showing CMR. These results open new avenues for material design for functional magnets in the family of double perovskites.
Related publication: “Colossal magnetoresistance in the insulating ferromagnetic double perovskites Tl2NiMnO6: A neutron diffraction study.” Acta Materialia 173 (2019) 20-26
Funding: EU Horizon2020, Rutherford International Fellowship Programme, ISIS co-funded studentship
Authors: L Ding, D D Khalyavin, P Manuel (ISIS), J Blake (Royal Holloway, University of London and ISIS), F Orlandi (ISIS), W Yi, A A Belik (National Institute for Materials Science, Japan)