PERMEABILITY MEASUREMENT ON FERROMAGNETIC THIN-FILMS FROM 50 MHZ UP TO 18 GHZ

The needs for permeability measurements on ferromagnetic materials at high frequencies are driven by the development of broad-band recording systems. However, measurements above 500 MHz on ferromagnetic films are difficult. Wide band permeability measurements are reported only up to a few GHz. Measurements at higher frequencies can be performed using resonant cavities, as it is done in ferromagnetic resonance, but only at discrete frequencies. In contrast, we present a technique for measuring high frequency permeability of ferromagnetic films over a wide band. It works in a frequency range (50 MHz to 18 GHz or higher) that allows direct observation of the gyromagnetic resonance even on non-saturated samples, and can yield permeability in different directions for anisotropic films. In our technique a surface of about 0.5 dm2 of the ferromagnetic material has to be wound to obtain proper sample geometry. As a consequence, our technique is restricted to coatings deposited on thin flexible substrates and to thin self supported ribbons produced by rapid solidification. Comparison with another measurement technique working up to 3 GHz, and with calculated gyromagnetic response, yield a satisfactory agreement. The limitations of our method are discussed. Spectroscopic permeability measurements are reported for several alloys.