DIRECT MEASUREMENT OF PERMEABILITY UP TO 3 GHZ OF CO-BASED ALLOYS UNDER TENSILE-STRESS

The high frequency permeability of CoNbZr and CoZrMoNi prepared by mag netron sputtering, and of CoFeSiB deposited by ion beam sputtering was investigated. The layers were deposited on thin (8-12 mum) mylar film s, and it was therefore possible to induce large tensile stress with m oderate force. The permeability of the layers was measured along the s tress direction, in a frequency range that allowed the observation of the rotational permeability and the gyromagnetic resonance. The resona nce frequency of CoNbZr shifted from 1.4 to over 3 GHz under stress. A simple model assuming that the easy axis is constant over the whole f ilm predicts the evolution of resonance frequency and initial permeabi lity. This model is in good agreement with measurements on CoZrMoNi, a nd yields a satisfactory estimation of the magnetostriction coefficien t. In the case of CoNbZr, a poorer agreement is attributed to the disp ersion of local magnetization direction. For very large stress, cracks in the ferromagnetic films are expected to participate to the increas e in the anisotropy field. It was observed that the linewidth of the r esonance is slightly affected by the stress.