Magnetic properties of amorphous magnetic alloys

Low-field magnetic properties of amorphous ferromagnetic alloys have been previously reported mainly at d.c. The alloys in ribbon form generally show square hysteresis loops, with coercive fields less than 0.1 Oe, and with saturation magnetization up to 17000 G. Maximum magnetization is obtained in low fields only when the ribbons are under tensile stress. This paper reports further measurements on amorphous magnetic alloys, including differential scanning calorimeter data on the crystallization of three compositions and a variety of a.c. measurements on toroidal samples at frequencies up to 2000 Hz. The coercive fields and magnetic losses under a.c. excitation are disappointingly high. This is attributed to an increase in coercive field when straight ribbon is wound into toroidal form, and to a further increase in Hcwith frequency due to an apparent decrease in the number of domain walls participating in the magnetization reversal. Neither effect is necessarily inherent in amorphous magnetic materials.