Peculiarities of crystallization and formation of magnetic properties of amorphous alloys in heating

The paper describes analysis of the structure and the complex of magnetic properties of 25 x 15 x 10 mm sized magnetic circuits weighing 18-22 g made of Fe or Co based amorphous alloy ribbon 20-30 µm in thickness. It is been demonstrated that the crystallization process during continuous heating of all amorphous alloys proceeds in two stages in near temperature ranges of 500-600 and 650-750 °С. Crystallization at the beginning of the first range, when the formed amorphous-nanocrystalline state forms, results in additional improvement of magnetic properties of all alloys. The higher complex of magnetic properties (very low coercive force HcM = 0.67 T and permeability μmax > 105, low degree of hysteresis loop squareness Br /Bmax = 0.4-0.5) is formed in magnetic circuits from a Finemet type alloy after annealing at 500-560 °С when the dimensions of emerging nanocrystals make 14-15 nm. An increase of temperature above the optimal range for each alloy causes intensive development of crystallization, leads to increase in size of the formed crystallites and worsens the complex of magnetic properties. Annealing of magnetic circuits from a Finemet type alloy at temperatures of 590-600 °С, where the first range of crystallization ends, has little effect on the degree of crystallization, but leads to an increase of crystallite size resulting in a decrease of saturation induction and an increase of coercive force.