Magnetic properties of field-annealed amorphous Fe-B-Si wound cores

The effects of annealing with and without a magnetic field on the coercive force and loss of cobalt-free amorphous Fe-B-Si wound cores have been investigated as a function of the annealing temperature and field to improve the properties of the ribbon cores. As-wound cores have square B-H loops with high coercive force and low remnant magnetization due to the presence of magnetically hard regions in the ribbons. The remnant magnetization increases, and the coercive force and loss of wound cores become a minimum when they are annealed without a field at 410 degree C due to the removal of stresses and the occurrence of crystallization at higher annealing temperature. Near 180 degree domains exist in the thermally annealed toroid cores, but the domain walls are not parallel to the longitudinal direction of the ribbon. In the specimen annealed with 10 Oe at 390 degree C, the domains are parallel to the longitudinal direction due to the field-induced uniaxial anisotropy. These result in a further increase in the remnant magnetization and a decrease in the coercive force and loss. Total core loss, measured at 1.2 T and 60 Hz, of the wound core annealed at 390 degree C with field of 10 Oe was 0.15 W/kg