Elevated temperature initial permeability study of some ferromagnetic alloys

An in situ measurement technique was designed to investigate temperature de pendence of initial permeability (mu(i)) for three soft magnetic materials: Ni79Fe16Mo5 Supermalloy, amorphous Co65Fe4Ni2Si15B14 alloy and nanocrystal line Fe73.5Cu1Nb3Si13.5B9 alloy. For the Ni79Fe16Mo5 Supermalloy, a small d iscrepancy on mu(i)-T curve was observed between the heating and cooling pr ocesses and the Curie temperature (T-c) was obtained around 400 degrees C i n accordance with the Hopkinson effect. An annealing temperature at a value of similar to 450 degrees C is found sufficient to release the residual st ress effect of the rewound core. For the amorphous Co65Fe4Ni2Si15B14 alloy, a very strong domain wall stabilization effect associating with a sharp va lley on the mu(i)-T curve at the temperature ranging from 110 degrees C to 180 degrees C is identified during the heating process. In addition, the T- c peak around 225 degrees C obtained during heating matches that during coo ling. For the Fe73.5Cu1Nb3Si13.5B9 alloy, the amorphous T-c value can be de tected to be around 325 degrees C during the heating process. However, duri ng the cooling process two magnetic Curie transitions were found to be simi lar to 581 degrees C and 262 degrees C corresponding to alpha-Fe (Si) nanoc rystal and residual amorphous phase, respectively. The improvement in the r oom temperature mu(i) value for the above materials can be achieved after i n situ annealing studies. (C) 1998 Elsevier Science S.A. All rights reserve d.