Temperature dependence of the coercivity and the anisotropy of Nd-Fe-B based magnets

The temperature dependence of the coercivityxHcand the anisotropy field HAfrom Nd-Fe-B based sintered permanent magnets was measured from 100K up to the Curie temperature. A Pr18Fe77B8magnet and a series of the compositions Nd14.8Dy1.8(Fe77.8-xCox)B7(x=0,10,20) were studied in order to achieve improvements of the temperature characteristic above room temperature. The Co substitution increases naturally the Curie temperature but it chances HAat room temperature only slightly. The coercivity however is reduced so drastically, that the temperature behaviour of the sample with x=20 is comparabel to that of a pure Nd-Fe-B magnet. The best results in this respect were achieved with a heavy rare earth substituted material (x=0) and with the Pr18Fe77B8sample. Additionally it was tried to correlatexHc(T) and HA(T) using two different models in order to get information about the coercivity mechanism. The results thus obtained are in general agreement with the usual picture of the coercivity mechanism valid in Nd-Fe-B based magnets.