Advances in Ferromagnetic Metallic Glasses

Recent developments in transition metal glasses have resulted in the synthesis of an iron‐rich glass (nominal composition, Fe80B20) in continuous ribbon form. The as‐quenched glass shows a saturation moment of 1.99 μB/Fe atom at 4.2 K, an induction of 16 kG at 300 K, a ferromagnetic Curie temperature of 650 K, a saturation magnetostriction of 30 × 10−6 and a coercivity Hc of about 100 mOe. Large domains, elongated parallel to the ribbon axis, are observed. Both Mössbauer and FMR data indicate that the magnetic anisotropy (K = 3 × 104 erg/cm3) is in the ribbon plane. Evidence is presented that boron donates less electrons to the d‐band of transition metal atoms compared with other glass‐forming metalloids such as phosphorous. Some of the low‐field properties include: the permeability at 20 G, μ(20) = 1,700, μmax = 102,000 and core‐loss, W ≃ 0.3 to 0.4 watts/kg at f=1 kHz and Bmax = 1 kG. Field annealing results in improvements in these properties: A typical field‐annealed toroid shows Hc∼40 mOe, μ(20) = 4,000, μmax = 320,000 and W = 0.1 watts/kg at f = 1 kHz and Bmax = 1 kG. These properties represent significant improvements over existing iron‐base metallic glasses and their commercial crystalline alloy counterparts.