Soft Magnetism and High Frequency Properties of Fe₆₅Co₃₅-MgF₂ Granular Thin Films

(Fe₆₅Co₃₅)_x(MgF₂)_1-x films with different metal volume fraction x are fabricated by magnetron sputtering. The results reveal that good soft magnetic properties can be obtained in a very wide x range (0.9> x >0.55) with H_c not exceeding 10 Oe, and high resistivity is also realized for the samples. Especially for the sample with x= 0.75, the coercivity in hard and easy axes is 1.6 Oe and 8.5 Oe, respectively, 4π M_s=14.1 kG and ρ reaches 1.16 mΩcdotcm. The dependence of complex permeability μ =μ- jμ'' on frequency shows that the real part μ' is more than 190 below 2.0 GHz and ferromagnetic resonance frequency f_r reaches 2.43 GHz, implying that the film is promising for high frequency applications. High resolution transmission electron micrographs show that the films consists of bcc Fe₆₅Co₃₅ particles embedded uniformly in an amorphous insulating MgF₂ matrix with particle size around a few nanometers. The excellent soft magnetic properties and high frequency properties are ascribed to exchange of coupling among magnetic granules, and the exchange coupling variation in a wide x range (0.9> x >0.55) is studied systematically byΔ M plots.