Grain size dependence of coercivity in magnetic metal-insulator nanogranular films with uniaxial magnetic anisotropy

摘要

Excellent soft magnetic properties and appropriate uniaxial magnetic anisotropy field have been achieved in a wide metal volume fraction (x) range for as-deposited (Fe65Co35)x(SiO2)1-x granular films fabricated by magnetron sputtering. With decreasing x from 0.86 to 0.53, the coercive force of easy axis Hce decreases clearly and shows the minimum value (Hce=0.85 Oe) at x=0.53. More importantly, not only nanoscale grain-size D contributing to small coercivity is proved, but also a D3 dependence of Hce is observed in the range of 0.53u0003C;xu0003C;0.86, which is similar to the results of Suzuki etal reported for nanocrystalline alloys. Based on the random anisotropy model of Suzuki and Herzer, the grain-size D dependence of coercivity Hce in our metal-insulator granular film system was analyzed. Analyze results indicate that strong coherent uniaxial anisotropy which dominates over the random anisotropy of magnetic grains obtained by the random anisotropy model can be responsible for the D3 dependence of the coercivity Hce. In addition, in the range of 0.42u0003C;xu0003C;0.53, Hce (as well as Heh) increases with increasing x and then the -nD dependence of Hce deviates greatly from the D3 law, which is ascribed to the decrease in intergranular exchange coupling due to the increase in SiO2 insulator layer.