Investigation Of Magnetostriction And Effective Magnetic Anisotropy For Co-contained Finemet-type Nanocrystalline Alloys

The microstructures and magnetic properties of (Fe_0.5Co_0.5)_73.5Nb₃Si_13.5B₉Cu₁,(Fe_0.5Co_0.5)_73.5Nb2V1Si13.5B9BCu1 and (Fe_0.5Co_0.5)_73.5Mo3Si13.5BB9Cu1 amorphous alloys annealed at various temperatures were investigated.The dependence of magnetostriction and effect magnetic anisotropy on annealing temperature for above three FeCo-based alloys were mainly studied. The results show that, a two-phase nanocrystalline structure composed of the amorphous matrix and theα-FeCo(Si) nanocrystallites is obtained by nanocrystallization annealing and the annealing temperature have great influence on microstructures and magnetic properties. With annealing temperature increasing, the grain size and the volume fraction of crystallization phase gradually increased, which results in the change of the soft magetic properties.The saturation magnetostrictionsλs for nanocrystalline (Fe_0.5Co_0.5)_73.5Nb3Si13.5B9Cu1,(Fe_0.5Co_0.5)_73.5Nb2V1Si13.5B9Cu1 and (Fe_0.5Co_0.5)_73.5Mo3Si13.5BB9Cu1 alloys were evaluated by means of small-angle magnetization rotation. The saturation magnetostrictions(about 20-90ppm) increase with the annealing temperatures because of the positive saturation magnetostriction of crystallineα-FeCo(Si) phase which is larger than that of amorphous phase. So with the increasing of annealing temperature, the volume of crystalline phase become large which results in the increasing ofλs. The same change tendency was observed for the Coercivity Hc and the saturation magnetostriction. This proves that saturation magnetostriction has a great influence on soft magetic properties. The effect magnetic anisotropy of nanocrystalline (Fe_0.5Co_0.5)_73.5Nb3Si13.5B9Cu1,(Fe_0.5Co_0.5)_73.5Nb2V1Si13.5B9Cu1 and (Fe_0.5Co_0.5)_73.5Mo3Si13.5B9BCu1 alloyswas measured by means of the law of approach to saturation.The result shows that the change tendency of the with annealing temperatures is different from the Hc. The change tendency of theλs with annealing temperature for FeCo-based alloys was opposite with Fe-based alloys. The larger magnetostriction of FeCo-based alloys results in much higher coercivity than that of Fe-based alloys. The addition of Co enhanced magnetostriction coeffficient greatly by a order of magnitude, resulting in the increasing of coercivity which well demonstrates the reason why the magnetic properties of FeCo-based alloys are quite harder than that of FINEMET at room temperature. The dependence of magnetostriction coeffficient and effect magnetic anisotropy on addtion of V, Mo and other chemical elements were also discussed.