ANGULAR-DEPENDENCE OF COERCIVITY IN ND-FE-B SINTERED MAGNETS - PROOF THAT COHERENT ROTATION IS NOT INVOLVED

An experimental procedure is presented which allows the analysis of the angular dependence of the coercivity of polycrystalline samples H-c(theta) in terms of the angular dependence of the switching field of the individual grains forming the material, H-s(theta'). The method is based on the measurement of the remanence curves corresponding to three different field configurations (in which the demagnetizing field is directed antiparallel, perpendicular, and almost parallel to the saturating field, respectively). By using this procedure we have studied the angular dependence of the coercivity in sintered oriented magnets based on the Nd2Fe14B hard phase. According to our results the switching field of the individual crystallites increases monotonically from approximately 0.15H(A), H-A being the anisotropy field, for those whose easy axis is oriented parallel to the demagnetizing field (theta' = 0 degrees), to values close to H-A, for those whose easy axis is perpendicular (theta' = 90 degrees), and follows closely a 1/cos theta' law up to theta' = 50 degrees. This shows that the magnetic anisotropy value in the regions where the nucleation takes place during the reversal of magnetization is not far from the bulk value, and also that coherent rotation is not the determinant mechanism among those governing the nucleation process.