Inhibition of abnormal acicular grain growth of nanostructured Ba–ferrite films by secondary α-Fe2O3 phase

Abstract

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 SiO2 substrate is naturally crystallized into the abnormal acicular Ba–ferrite grains (major axis of ∼1000 nm in the in-plane direction). However, on α-Al2O3 substrate, fine grain sizes of the primary Ba–ferrite phase (∼70 nm) are obtained during crystallization. Nucleation of the α-Fe2O3 phase on the α-Al2O3 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-Al2O3 film enhances 4.4 kOe, much larger than that of Ba–ferrite/SiO2 film (1.9 kOe). We suggest that the secondary α-Fe2O3 phase act as a useful inhibitor to abnormal grain growth in Ba–ferrite films for high-density recording media.