Thermal Stability and Magnetic Properties of Fe–Co–Pr–B Amorphous Alloys with a Supercooled Liquid Region

Abstract

The thermal stability, crystallized structure and magnetic properties of melt-spun Fe_70−xCo₁₀Pr_xB₂₀ (0≤x≤6) amorphous alloys have been investigated. The glass transition followed by a supercooled liquid region (ΔT_x) was observed in the composition range of 2 to 5 at%Pr and the value of the ΔT_x is in the range of 23 to 43 K. The good hard magnetic properties were obtained for the alloys containing 2.5 to 5 at%Pr subjected to an optimum heat treatment. The ΔT_x and reduced glass transition temperature (T_g⁄T_m) of the 3.5 at%Pr alloy are 43 K and 0.57, respectively. The crystallized structure consists of (Fe, Co)₃B, α-(Fe, Co) and Pr₂(Fe, Co)₄B phases and their average grain sizes after annealing for 420 s at 863 K are about 25 nm. The remanence (B_r), coercivity (_iH_c) and maximum energy product (BH)_max of the optimally annealed the 3.5 at%Pr alloy are 1.36 T, 211 kA/m and 107 kJ/m³, respectively. The good hard magnetic properties in the crystallized state of the Fe–Co–Pr–B amorphous alloys with high glass-forming ability indicates the possibility of future fabrication of a bulk hard magnetic material by the simple process of the formation of a bulk amorphous alloy followed by crystallization.