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

Magnetic domain structure and switching mechanism were investigated in indi vidual barium ferrite gains with sizes ranging from 0.5-7 mu m. Magnetic fo rce microscopy (MFM) was used to image grains in sputtered Pt-doped barium ferrite thin films. The switching thresholds of the different grains were m easured by applying successively larger magnetic fields to the sample and o bserving which grains switched, Application of a held to as-annealed sample s swept out multidomain structures at a field of H-ini approximate to 1000 Oe, which was relatively independent of grain size. It was found that, afte r 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 (abou t 4 mu m) H-ini approximate to H-rev; whereas for grains with sizes of 1-3 mu m, 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 lar ger than 4 mu m, as suggested by discontinuous magnetization jumps and an i nverse-cosine angular dependence of H-rev. Reversal in grains with sizes be tween 0.5 and 1 mu m is believed to be dominated by incoherent rotation, as indicated by the angular dependence of H-rev.