Onfluence of oxygen stoichiometry on transport, optical and magnetic properties of the room-temperature ferrimagnetic oxide semiconductor Fe_1.5Ti_0.5O_3-δ

Iron-titanium oxide Fe_1.5Ti_0.5O_3-d obtained by substituting iron by titanium in the hematite structure alpha-Fe_2O_3 is proposed as a "spintronic" material beyond room-temperature: experimental results on bulk and thin films show Fe_2-xTi_xO_3-d to be both magnetic and semiconducting depending on Ti content. Although pure ilmenite FeTiO_3 and pure hematite alpha-Fe_2O_3 are antiferromagnets and insulators, ab-initio calculations predict a half-metallic behaviour for x=0.5. We present here the results obtained for Fe_1.5Ti_0.5O_3-d on epitaxial thin films, grown by pulsed laser deposition technique on c-sapphire at various oxygen pressures (P_O2). The magnetic properties were investigated by SQUID, the electrical properties using classical resistance and Hall effect, and optical absorption using UV-Vis-NIR spectrophotometer. For all oxygen pressures, epitaxial films are single phase. P_O2 appears to be critical parameter for both magnetic and semiconducting properties. High n-type conductivity is obtained at low P_O2 whereas high saturation magnetization M_S and remanence M_R stands for high P_O2 (see fig). Optical absorption data allow associating conduction with the formation of an impurity band.