High frequency characteristics of (Ni₇₅Fe₂)_x(ZnO)_1-x granular thin films with tunable damping coefficient

The effect of the volume fraction of ferromagnetic metal (x) in (Ni₇₅Fe₂₅)_x(ZnO)_1-x nanogranular thin films on microstructural, soft-magnetic, and high-frequency properties was investigated. Good soft-magnetic properties were obtained in a broad x range, with 0.55 < x < 0.82. High resolution transmission electron microscopy (HRTEM) observations reveal that the grain size of the samples is lower than 14 nm, and that it decreases with decreasing x. Of special interest, our investigation of the permeability spectra indicates that these films exhibit an adjustable frequency linewidth of resonance peak, dependant upon changing x. Correspondingly, large and adjustable damping coefficients (α_eff) from 0.023 to 0.043 were achieved by decreasing x from 0.82 to 0.55. Combined with the HRTEM results, the variation of α_eff with x was analyzed in detail.