Thickness dependence of the crystallization of Ba-ferrite films

The crystallization of Ba-ferrite/sapphire(001) films of various thicknesse s has been studied using synchrotron x-ray scattering, field emission scann ing electron microscope, and atomic force microscope. In films thinner than 1000 Angstrom, Ba-ferrite amorphous precursor was crystallized into perpen dicular grains keeping the magnetically easy c-axis normal to the film plan e during annealing to 750 degrees C. In films thicker than 1000 Angstrom, h owever, acicular grains keeping the c-axis parallel to the film plane were grown on top of the perpendicular grains. The behavior of the saturation ma gnetization and the intrinsic coercivity was consistent with the thickness dependence of the crystallization. We attribute the thickness dependence of the crystallization to the substrate effect, which prefers the growth of t he epitaxial, c-axis oriented perpendicular grains near the film/substrate interfacial area. (C) 1999 American Institute of Physics. [S0021-8979(99)01 016-6].