Fabrication and Magnetic Properties of $\hbox {Fe}_{65}\hbox {Co}_{35}\hbox {-}\hbox {B}_{2}\hbox {O}_{3}$ Granular Films for High Frequency Application

A series of (Fe₆₅Co₃₅)x(B₂O₃>)_1-x nano-granular films with different metal volume fractions x were fabricated by magnetron sputtering. High resolution transmission electron micrographs show that the film consists of bcc Fe₆₅Co₃₅ particles uniformly embedded in an amorphous insulating B₂O₃ matrix with particle size around a few nanometers. With the decrease in x from 0.66 to 0.55, the films exhibit coercivity H_C not exceeding 16 Oe, along with high resistivity. Especially for the sample with x=0.61, coercivities in hard and easy axes are 3 and 13.4 Oe, respectively, 4piM_S=12.5 kG, and rho reaches 2.38times10³ muOmegaldrcm. The dependence of complex permeability mu = mu´-jmu´´ on frequency shows that the real part mu´ is more than 170 below 1.5 GHz and ferromagnetic resonance frequency reaches 2.65 GHz. The good soft magnetic property is ascribed to the exchange coupling among magnetic granules. The investigation of the DeltaM-H curve evidences the existence of this inter-granule interaction.