ELECTRIC AND MAGNETIC PROPERTIES OF EPITAXIAL Fe_(2-x)Ti_xO_(3+delta)FILMS

摘要

Solid solution films of the alpha-Fe2O3-FeTiO3 series are one of the candidates for noble half-metallic oxides. They were epitaxially formed on alpha-Al2O3(001) single crystalline substrates by O2-reactive evaporation method. The Fe_(2_x)Ti-xO_(3+delta) films prepared at higher T_S=973 K and with larger Ti content x>=0.4 had the ilmenite structure with R3 symmetry. Other films at lower T_s or with smaller x possessed the corundum structure with R3c. Only the films with R3 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～(_1)OMEGA cm due to the formation of the mixed valence states between Fe～(2+) and Fe～(3+). However the Fe～(2+) content of the films was rather small as compared with stoichiometric Fe_(2_x)Ti_xO3. The Ti-rich films had large oxygen nonstoichiometry of about delta=0.3.