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 th e angular dependence of the coercivity of polycrystalline samples H-c( theta) in terms of the angular dependence of the switching field of th e individual grains forming the material, H-s(theta'). The method is b ased on the measurement of the remanence curves corresponding to three different field configurations (in which the demagnetizing field is d irected antiparallel, perpendicular, and almost parallel to the satura ting field, respectively). By using this procedure we have studied the angular dependence of the coercivity in sintered oriented magnets bas ed on the Nd2Fe14B hard phase. According to our results the switching field of the individual crystallites increases monotonically from appr oximately 0.15H(A), H-A being the anisotropy field, for those whose ea sy axis is oriented parallel to the demagnetizing field (theta' = 0 de grees), to values close to H-A, for those whose easy axis is perpendic ular (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 nu cleation process.