CORRELATION BETWEEN STRUCTURE AND THE MAGNETIC-PROPERTIES OF AMORPHOUS AND NANOCRYSTALLINE FE73.5CU1NB3SI22.5-XBX ALLOYS

The effects of the metalloid composition and annealing temperature (400-720-degrees-C) on the magnetic properties of Fe73.5Cu1Nb3Si22.5-xBx, (x = 5-10 at%) nanocrystalline alloys have been investigated. Crystallization products were studied using X-ray diffractometry. The coercive field, remanence and out of ribbon axis anisotropy were determined from quasi-static hysteresis loops. It was found that the beginning of nanocrystallization causes some magnetic hardening, which is manifested in a remarkable increase in coercive field for all the alloys studied. This effect is ascribed to the increase in magnetostriction. The softest magnetic behavior was observed for alloys with nanocrystalline structure composed of alpha-Fe(Si), Fe3Si and an amorphous matrix. The very strong magnetic hardening coincides with the second stage of crystallization and the appearance of borides (e.g. Fe2B). The Si-rich alloys also exhibit minor hardening after annealing at temperatures well below the onset temperature of the second stage of crystallization. This effect is attributed to the increase in grain size and the precipitation of copper crystals.