Electric and magnetic properties of epitaxial Fe_2-xTi_xO_3+δ films

Solid solution films of the α-Fe₂O₃-FeTiO₃ series are one of the candidates for noble half-metallic oxides. They were epitaxially formed on α-Al₂O₃(001) single crystalline substrates by O₂-reactive evaporation method. The Fe_2-xTi_xO_3+δ films prepared at higher T_S=973 K and with larger Ti content x ≥ 0.4 had the ilmenite structure with R3̄ symmetry. Other films at lower T_S or with smaller x possessed the corundum structure with R3̄c. Only the films with R3̄ symmetry had large ferrimagnetic moments, though the observed spontaneous magnetization was less than half of the ideal value expected from the fully ordered structure. Room temperature resistivity of intermediate composites dropped to 10^-1Ωcm due to the formation of the mixed valence states between Fe²⁺ and Fe³⁺. However the Fe²⁺ content of the films was rather small as compared with stoichiometric Fe_2-xTi_xO₃. The Ti-rich films had large oxygen nonstoichiometry of about δ=0.3.