Development of Magnetic Properties during Annealing of Hf_2Co_{11}B Amorphous Alloy

Abstract

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 Ta = 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 mr. Value of mr, for Ta = 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/cm 3 for the amorphous ribbon to 15.84 Merg/cm 3 for the sample annealed at 650• C for 30 min.

Influence of cooling rate on the magnetic properties of Hf–Co–Fe–B melt-spun alloy

“…In this direction, the scientific community has been focussing on several rare-earth-free permanent magnet materials, as they can be potential substitutes for rare-earth permanent magnets [5][6][7][8][9]. Among the possible materials, Hf-Co based alloys exhibit favourable magnetic properties including high magnetocrystalline anisotropy (K 1 ) ~ 10 Mergs cm −3 , high Curie temperature (T C ) ~ 477-497 °C and high magnetic polarization (J s ) ~ 10 kG (J s = 4πM s ) [10][11][12][13] that are associated with the presence of HfCo 7 or Hf 2 Co 11 hard magnetic phases [11,[14][15][16][17][18]. HfCo 7 crystallizes in orthorhombic structure, while Hf 2 Co 11 crystallizes in rhombohedral and orthorhombic crystal structures [17], yet structural similarity between these phases have been reported earlier [19].…”

“…Hf-Co based alloys have been widely studied as an important class of rare-earth-free permanent magnet material [9-11, 13, 14, 16-30]. However, multi-step synthesis process including complex heat treatments and mechanical alloying are requisite for the enhancement of permanent magnetic properties [13,18,23,29,[31][32][33]. Several experimental studies on melt spinning [13,17,18,23,[34][35][36][37] reveal that the evolution of hard magnetic behaviour in this class of alloys is strongly annealing dependent.…”

“…However, multi-step synthesis process including complex heat treatments and mechanical alloying are requisite for the enhancement of permanent magnetic properties [13,18,23,29,[31][32][33]. Several experimental studies on melt spinning [13,17,18,23,[34][35][36][37] reveal that the evolution of hard magnetic behaviour in this class of alloys is strongly annealing dependent. The experimental investigation on variation in wheel speed is reported only by McGuire et al on the synthesis of Hf 2 Co 11 B alloys to obtain magnetically hard nanocrystalline phases [11].…”