Oxygen defect assisted paramagnetic to ferromagnetic conversion in Fe doped TiO2 nanoparticles

Abstract

Here we report the magnetic properties of Fe doped TiO₂ nanoparticles annealed in air and vacuum. Fe doped TiO₂ nanoparticles display paramagnetism during air annealing and ferromagnetism when the samples are annealed under vacuum. Ferromagnetism in vacuum annealed pure TiO₂ nanoparticles is because of the presence of a high density of paramagnetic oxygen vacancy centers. Ferromagnetism in vacuum annealed Fe doped TiO₂ is because of the strong exchange interaction of lattice site Fe³⁺ ions with the nearest paramagnetic oxygen vacancies by forming bound magnetic polarons (BMPs). A collective contribution of the magnetic moment from the bound magnetic polaron on the lattice site and from the paramagnetic oxygen vacancies on the surface and on the grain boundary results in the conversion of paramagnetism to ferromagnetism in vacuum annealed Fe doped TiO₂.