Oxygen defect assisted paramagnetic to ferromagnetic conversion in Fe doped TiO₂nanoparticles

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.