Magnetic properties of amorphous (Fe 1 - xCo x) 77.5Nd 4B 18.5 alloys and the effects of heat treatment on its hard magnetic properties

Abstract

The magnetic moment and Curie temperature of amorphous (Fe 1 - x Co x ) 77.5Nd 4B 18.5 (0 ≤ x ≤ 0.4; 1.0) alloys and the effects of heat treatment on its hard magnetic properties were studied. The Nd magnetic moment in the amorphous samples are present as a speromagnetic structure. The Fe atom moment is found to increase from 2.0μ B for x = 0 to 2.27μ B for x = 0.4, as the Co atom moment is assumed to keep a value of 1.21μ B over the whole concentration. The Curie temperature of these amorphous alloys increases remarkably with increasing Co concentration. This behavior is due to the stronger exchange interactions between Fe-Co atoms than that of Fe-Fe and Co-Co atoms. The intrinsic coercive field i H c and maximum energy product ( BH) max obtained under optimal annealing conditions are found to decrease monotonically with increasing Co concentration, but appear at higher values of 2.3–3.0 kOe and 11.6–13.5 MGOe for x ≤ 0.2, respectively. The hard magnetic properties in the crystallized FeCoNdB alloys are proved to be due to the presence of some hard magnetic 2:14:1 phase. The Co substitution for Fe results in an increase in T c of the 2:14:1 phase, improving the thermostability of these materials.