Magnetism at grain boundary interfacesin the colossal permittivity dielectric material; In+Nb Co-Doped Rutile

With the emphasis in recent years on understanding novel materials with potential technological applications this work seeks to understand magnetic ordering within the colossal-permittivity material, In+Nb co-doped rutile (TiO$_2$). Evidence for a spin-freezing transition was reported from a step like feature in the dielectic data below 50 K but this was largly glossed over. Within this work we show that below 300 K there is a slowing down of magnetic fluctuations associated with the electronic magnetism due to the defect-dipoles created by the co-doping, but the muon spectroscopy results are strongly suggestive of the behaviour being localised to the edges/interfaces of particles/grains. The $T_{\rm C}$ is strongly dependent on the doping level of the samples that presents novel way to control the magnetism and ultimately magneto-electric coupling within a dielectric material.