Tuning the conductivity type in a room temperature magnetic oxide: Ni-doped Ga0.6Fe1.4O3 thin films

Abstract

Ni-Doped thin films of the room temperature ferrimagnetic oxide Ga_0.6Fe_1.4O₃ were deposited by pulsed laser deposition and their electronic transport and structural and magnetic properties were studied. The actual insertion of the Ni cations within the Ga_0.6Fe_1.4O₃ structure has been checked by resonant X-ray scattering. A clear extremum is noticed for all properties for the 2% Ni doping: extrema in the crystallographic cell parameters of the films, maximum in the Curie temperature, and maximum in the electric resistivity. We also observed a change of conductivity type for this dopant concentration, from n-type for Ni contents below 2% to p-type for Ni contents above 2%. We explain this behavior by the existence of oxygen vacancies in the pulsed laser deposited Ga_0.6Fe_1.4O₃ thin films, which results in the reduction of some of the Fe³⁺ into Fe²⁺ cations, and n-type conduction via a hopping mechanism. The insertion of Ni²⁺ cations first deals with the presence of oxygen vacancies and reduces the number of n-type carriers in the films, in a compensation-like mechanism. When the number of introduced Ni²⁺ cations dominates the number of oxygen vacancies, conductivity becomes p-type and starts to increase again. We believe that the tunability of the conduction type and magnitude in thin films of a room temperature ferrimagnetic material paves the way towards new all oxide electronic devices.