Observation of magnetic domain structure and switching in barium ferrite thin films

Magnetic domain structure and switching mechanism were investigated in individual barium ferrite grains with sizes ranging from 0.5-7 μm. Magnetic force microscopy (MFM) was used to image grains in sputtered Pt-doped barium ferrite thin films. The switching thresholds of the different grains were measured by applying successively larger magnetic fields to the sample and observing which grains switched. Application of a field to as-annealed samples swept out multidomain structures at a field of H_ini≈1000 Oe, which was relatively independent of grain size. It was found that, after the grains had been saturated, a different field H_rev had to be applied to saturate the grain in the opposite direction in large size grains (about 4 μm) H_ini≈H_rev; whereas for grains with sizes of 1-3 μm, H_rev varies from approximately equal to H_ini to many times larger. Domain wall motion was found to dominate the reversal process in grains larger than 4 μm, as suggested by discontinuous magnetization jumps and an inverse-cosine angular dependence of H_rev. Reversal in grains with sizes between 0.5 and 1 μm is believed to be dominated by incoherent rotation, as indicated by the angular dependence of H_rev