EPITAXIAL-GROWTH AND MAGNETIC-BEHAVIOR OF NIFE2O4 THIN-FILMS

Thin films of NiFe2O4 were deposited on SrTiO3 (001) and Y0.15Zr0.85O2 (yttria-stabilized zirconia) (001) and (011) substrates by 90 degrees -off-axis sputtering. Ion channeling, x-ray diffraction, and transmiss ion electron microscopy studies reveal that films grown at 600 degrees C consist of similar to 300 Angstrom diameter grains separated by thi n regions of highly defective or amorphous material. The development o f this microstructure is attributed to the presence of rotated or disp laced crystallographic domains and is comparable to that observed in o ther materials grown on mismatched substrates (e.g., GaAs/Si or Ba2YCu 3O7/MgO). Postdeposition annealing at 1000 degrees C yields films that are essentially single crystal. The magnetic properties of the films are strongly affected by the structural changes; unannealed films are not magnetically saturated even in an applied field of 55 kOe, while t he annealed films have properties comparable to those of bulk, single crystal NiFe2O4. Homoepitaxial films grown at 400 degrees C also are e ssentially single crystal.