Low-field magnetic properties of Fe80B20 glass

Abstract

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 (λ_s=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 0.77B_s(B_s=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).