Development of magnetic properties during annealing of Hf₂Co₁₁B amorphous alloy

Influence of heat treatment on magnetic properties of amorphous Hf₂Co₁₁B alloy was investigated. Hard magnetic phase, characterized by high magnetic anisotropy, appears during crystallization. The highest coercive field equal to 1.86 kOe, was obtained for sample annealed in third crystallization stage. Longer heat treatment at T_{a} = 650°C leads to decrease in coercive field, which can be the result of excess of the HfCo₃B₂ phase volume fraction and additionally eutectoid transformation of hard magnetic phase into soft magnetic Co₂₃B₆ and fcc-Co. Decrease of volume fraction of hard phase is confirmed by the remanence ratio m_{r}. Value of m_{r}, for T_{a} = 650°C, is decreasing with annealing time from 0.4 to 0.27 for 30 min and 120 min, respectively. The magnetocrystalline anisotropy constant K₁ increases from 2.23 Merg/cm³ for the amorphous ribbon to 15.84 Merg/cm³ for the sample annealed at 650°C for 30 min.