Inhibition of abnormal acicular grain growth of nanostructured Ba-ferrite films by secondary α-Fe ₂O ₃ phase

We have studied the inhibition of abnormal acicular grain growth of the Ba-ferrite phase in the crystallization of Ba-ferrite films using real time synchrotron x-ray scattering, field emission scanning electron microscope, and vibrating sample magnetometer. Amorphous Ba-ferrite film on a SiO ₂ substrate is naturally crystallized into the abnormal acicular Ba-ferrite grains (major axis of ∼1000 nm in the in-plane direction). However, on α-Al ₂O ₃ substrate, fine grain sizes of the primary Ba-ferrite phase (∼70 nm) are obtained during crystallization. Nucleation of the α-Fe ₂O ₃ phase on the α-Al ₂O ₃ surface at an early stage induces the inhibition of the abnormal acicular grain growth of the Ba-ferrite phase. Because of the grain size refinement of the magnetic Ba-ferrite phase, the intrinsic coercivity of Ba-ferrite/α-Al ₂O ₃ film enhances 4.4 kOe, much larger than that of Ba-ferrite/SiO ₂ film (1.9 kOe). We suggest that the secondary α-Fe ₂O ₃ phase act as a useful inhibitor to abnormal grain growth in Ba-ferrite films for high-density recording media.