Effect of Transversal Applied Bias Field on the Longitudinal Soft Magnetic Properties of Nanocrystalline Finemet Cores

In this work, we have investigated the effect of a transversal applied DC magnetic field on the longitudinally measured magnetic properties of nanocrystalline Finemet cores. The core was prepared by stacking up toroidal sheets (Dext = 17.5 mm, Dint = 8.5 mm) cut from 20 mm wide Finemet ribbon of 22 μmm thickness. The resulting height of the toroid was 5 mm. The stack was heat treated in hydrogen at 550°C for 1 h. Quantitative measurements were conducted by using a Helmholtz coil for generating the transversal field along the ring axis so that the magnetization of the toroidal core is forced to turn out of the sheet, transversal to the measuring magnetic field applied along the toroid. Flattening of the quasi-static loop as a function of transversal field is accompanied by a diminution of the remanence and coercive field. The relative permeability could be diminished by more than two orders of magnitude (from 60 000 to 700). Correspondingly, the eddy current frequency limit (where the imaginary part of the permeability is maximal) was shifted from 60 kHz to 1 MHz. Tayloring the hysteresis loop will be discussed in terms of rotational magnetization which dominates over the domain wall displacement mechanism when the magnetization is forced to turn out of the sheet plane.