For real world application in technological devices, materials are needed that show the novel dielectric behaviour of both high permittivity and low loss. This becomes even more interesting when they also exhibit magnetism. This coupling of electrical and magnetic properties is part of the recipe for multiferroics, which have great potential for use in future data storage devices.
Indium (In) and niobium (Nb) co-doped rutile (TiO2) is one such compound that shows high permittivity and low loss that would make it ideal for capacitive devices. The inclusion of both In3+ and Nb5+ ions into the structure creates Ti3+ defects; each with a single electron localised within it. Although the dielectric properties of this material have been investigated, the magnetic behaviour has previously been overlooked.
This work used muon spin relaxation (µSR), which is an ideal probe of weak magnetism, on both the MuSR and EMU instruments to study the magnetic properties of the material for the first time. The researchers found that magnetic ordering, associated with spin freezing, occurred at room temperature and below, with the precise temperature dependence being related to the level of doping. From the µSR measurements, evidence was found for the doping and associated spin freezing being confined to the grain boundaries, the place at which the defects preferentially occur.
This location of ordering suggests that the formation of the magnetically ordered state could be prompted to occur at a higher temperature by introducing more boundaries into the material in the form of nanoparticles or thin films. Therefore, doped nanoparticles could be the next step towards the formation of materials that could offer even more technological impact.
Related publication: “Understanding the role of electrons in the magnetism of a colossal permittivity dielectric material” Mater. Horiz., 2020,7, 188-192 DOI: 10.1039/C9MH00983C