Advances in Ferromagnetic Metallic Glasses

Abstract

Recent developments in transition metal glasses have resulted in the synthesis of an iron‐rich glass (nominal composition, ${\mathrm{Fe}}_{80}{\mathrm{B}}_{20}$ ) in continuous ribbon form. The as‐quenched glass shows a saturation moment of 1.99 μ_B/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 ${\text{30\hspace{0.17em}×\hspace{0.17em}10}}^{\text{−6}}$ and a coercivity H_c of about 100 mOe. Large domains, elongated parallel to the ribbon axis, are observed. Both Mössbauer and FMR data indicate that the magnetic anisotropy ($\mathrm{K}{\text{\hspace{0.17em}=\hspace{0.17em}3\hspace{0.17em}×\hspace{0.17em}10}}^4\hspace{0.17em}{\mathrm{erg/cm}}^3$ ) 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, $\text{μ(20)\hspace{0.17em}=\hspace{0.17em}1,700}$ , ${\mu }_{\max }\text{\hspace{0.17em}=\hspace{0.17em}102,000}$ and core‐loss, $\mathrm{W}\text{\hspace{0.17em}≃\hspace{0.17em}0.3\hspace{0.17em}}\mathrm{to}\text{\hspace{0.17em}0.4\hspace{0.17em}}\mathrm{watts/kg}$ at $\mathrm{f}\text{=1\hspace{0.17em}}\mathrm{kHz}$ and ${\mathrm{B}}_{\max }\text{\hspace{0.17em}=\hspace{0.17em}1\hspace{0.17em}}\mathrm{kG}$ . Field annealing results in improvements in these properties: A typical field‐annealed toroid shows ${\mathrm{H}}_{\mathrm{c}}\text{∼40\hspace{0.17em}}\mathrm{mOe}$ , $\text{μ(20)\hspace{0.17em}=\hspace{0.17em}4,000}$ , ${\mu }_{\max }\text{\hspace{0.17em}=\hspace{0.17em}320,000}$ and $\mathrm{W}\text{\hspace{0.17em}=\hspace{0.17em}0.1\hspace{0.17em}}\mathrm{watts/kg}$ at $\mathrm{f}\text{\hspace{0.17em}=\hspace{0.17em}1\hspace{0.17em}}\mathrm{kHz}$ and ${\mathrm{B}}_{\max }\text{\hspace{0.17em}=\hspace{0.17em}1\hspace{0.17em}}\mathrm{kG}$ . These properties represent significant improvements over existing iron‐base metallic glasses and their commercial crystalline alloy counterparts.