Thermal and Magnetic Properties of Fe–Co–Ln–B (Ln=Nd, Sm, Tb or Dy) Amorphous Alloys with High Magnetostriction

Abstract

A supercooled liquid region before crystallization was found in wide composition ranges of 0 to 65 at%Co and 1.5 to 7 at%Ln in Fe_90−x−yCo_xLn_yB₂₀ (Ln=Nd, Sm, Tb or Dy) amorphous alloys. The supercooled liquid region shows the largest value of 41 K for the Fe₄₇Co₃₀Sm₃B₂₀ alloy. Besides, an internal equilibrium state leading to the disappearance of the previous thermal history is achieved within a temperature interval of 15 K. Furthermore, the Fe–Co–Ln–B amorphous alloys exhibit soft ferromagnetism with saturated magnetization (B_s) of 0.84 to 1.66 T and coercivity (H_c) of 5.0 to 36 A/m at room temperature. In addition, a high magnetostriction (λ_s) exceeding 40×10⁻⁶ was observed in the composition range of 0 to 10 at%Co and 1.5 to 3 at%Ln (Ln=Sm, Tb or Dy) while the highest λ_s reaches 58×10⁻⁶ for Fe_68.5Co₁₀Ln_1.5B₂₀ (Ln=Sm or Tb), which is higher than the highest value (44×10⁻⁶) for previously reported amorphous alloys. All the Fe_68.5Co₁₀Ln_1.5B₂₀ amorphous alloys have good bending ductility. The tensile fracture strength, Vickers hardness and Young’s modulus of the Fe_68.5Co₁₀Sm_1.5B₂₀ amorphous alloy are 3220 MPa, 990 and 76.5 GPa, respectively. The good combination of high λ_s, high B_s, low H_c, large ΔT_x, good ductility and high mechanical strength is a promising new type of ferromagnetic bulk amorphous alloy.