Magnetic Resonance in Metal–Insulator Nanogranular Composites with Paramagnetic Ions in an Insulating Matrix

The room-temperature magnetic resonance spectra of metal–insulator (CoFeB) x (LiNbO 3 ) 100 – x and (CoFeB) x (Al 2 O 3 ) 100 – x nanogranular composite films with various ferromagnetic metallic phase contents x near the percolation threshold are investigated. The systems under study are characterized by a high concentration of paramagnetic ions dispersed in an insulator matrix between ferromagnetic granules. In addition to a usual ferromagnetic resonance signal, these films are found to exhibit an additional absorption peak in weak fields. In contrast to the usual ferromagnetic resonance excited by a transverse high-frequency magnetic field, the additional peak demonstrates a weak dependence of its amplitude on the resonance excitation geometry. The position of this peak depends on the composition of the system, the resonance excitation frequency ( f = 7–38 GHz), and the magnetic field orientation with respect to the film plane. This behavior is associated with the paramagnetic resonance of Fe 3+ ions, which are present in the insulator matrix and interact with ferromagnetic granules.