High-frequency study of magnetic and magnetoimpedance features of granular nanostructures

For granular nanostructured system (Co/sub 40/Fe/sub 40/B/sub 20/)/sub x/(SiO/sub 2/)/sub 1-x,/ the FMR absorption and derivative lines were detected for metal phase concentrations X=37-53% in the frequency band 10-50 GHz. As well GMR was measured for these specimens. The analysis of the FMR lineshape demonstrates a presence of the non-collinear magnetic phase such as the asperomagnetic or superparamagnetic ones for insulating compositions below the percolation threshold (X<47%). The GMI was observed for compositions close to the percolation concentration. The GMI was observed only for samples with noticeable tunnel-type magnetoresistance. It means that the origin of GMI in the samples is connected with high frequency spin-dependent tunneling. Since the GMI amplitude at 30-50 GHz (/spl delta/T/T=0.46%) is approximately the same as that for MRE in transmission mode at infrared frequencies, it confirms that spin-dependent tunneling does not depend on frequency in a wide frequency range.