Formation, crystallized structure and magnetic properties of Fe-Pt-B amorphous alloys

Abstract

An amorphous phase was formed for (Fe0.75Pt0.25) 100-xBx (x = 25 and 30) alloys by melt-spinning. Their crystallization temperature were 671 and 667 K, respectively. The amorphous alloys exhibited good soft magnetic properties. The crystallized structure consisted of γ1 -FePt (fct), Fe2B and γ-FePt (fcc) phases, and their average grain sizes were about 15 nm after annealing at 785 K for 900 s. The remanence (Br), reduced remanence (M r/MS), coercivity (iHc) and maximum energy product (BH)max were 0.96 T, 0.83, 340kA/m and 102.2 kJ/m 3, respectively, for the 25 at%B alloy, and 0.91 T, 0.82, 368 kA/m and 96.5 kJ/m3, respectively, for the 30 at%B alloy. The reversible demagnetization loop behavior was also confirmed. Consequently, the good hard magnetic properties are interpreted as resulting from exchange magnetic coupling among nanoscale hard γi-FePt and soft Fe2B and γ-FePt magnetic phases. © 2005 The Japan Institute of Metals.