Low-field magnetic properties of Fe80B20 glass

The low-field magnetic properties of Fe80B20 glass are examined. Measurements are reported for straight strips, stressed and unstressed, for as-cast/as-wound toroids and for field-annealed toroids. Due to the positive magnetostriction (λs=31×10−6) of the alloy, the low-field magnetic properties of strips are improved by applied tensile stress. Similarly, toroids annealed to remove compressive stresses induced by winding (cooled in a magnetic field) are superior to unannealed toroids. Field-annealed Fe80B20 toroids show a coercivity of ∼0.04 Oe, a permeability of 4000 at 20 G, and a remanence ratio of 0.77Bs(Bs=16 kG). The approach of the magnetization to saturation for field-annealed toroids indicates a magnetic anisotropy energy density of about 5×103 erg/cm3. This low magnetic anisotropy, as well as the low coercivity and high resistivity (145 μΩ cm±10%) exhibited by Fe80B20 lead to low core loss under ac excitation, i.e., 0.10 W/kg (measured at 1 kHz and a maximum induction of 1 kG on a field-annealed toroid).