Fabrication and study of Ni75Fe25-SiO2 granular films for high frequency application

Ni₇₅Fe₂₅-SiO₂ granular films are fabricated and studied for high frequency applications. The films of different metal volume fraction f_v are fabricated by magnetron co-sputtering and they have fcc Ni₃Fe structure determined by X-ray diffraction. Magnetic hysteresis loops show that the samples of f_v=0.81 have in plane uniaxial anisotropy. The resistivity ρ is shown to increase slowly with decreasing f_v then increases rapidly after f_v>0.7, while coercivity H_c decreases rapidly as f_v decreases from 0.81 to 0.52 and does not exceed 5 Oe. In this f_v range, good soft magnetic properties are obtained especially for the sample with f_v=0.52 in which ρ reaches 19000 μΩ·cm with negative temperature coefficient. This high ρ effectively depresses the eddy current loss as applying for high frequency range. These interesting behavior is understood by exchange coupling between nanoparticles.