A new method to determine the switching field distribution with application to barium ferrite powder

Abstract

A method to determine the switching field distribution Hs(■cr>gc0) of powder assemblies of magnetically hard materials with a random orientation of the easy axes is described. The method is based on the ferromagnetic resonance absorption and the measurements of remanence curves. Direct information about the switching field distribution is obtained from major and minor loops of the hysteresis of the microwave absorption loss. By fitting calculated remanence curves and measured remanence curves the switching field distribution and its distribution at each orientation angle ■cr>gc0 is obtained. The application of this method leads to switching field distributions for coprecipitated barium ferrite, which are strongly correlated to the predictions of the theory of coherent rotation. The distribution of Hs for this sample is made narrower by an etching process or by magnetic dilution. For barium ferrite prepared by the conventional oxid ceramic method with additional milling, a monotonic increase of the switching field with increasing orientation angle is found. This increase is much smoother than the Kondorsky function provides.