Promotion of crystallization and magnetic property improvement enhancement of the energy product in Nd5.5Fe66B18.5Cr5Co5 by magnetic field heat treatment

Abstract

An externally applied magnetic field during heat treatment of a melt spun Nd5.5Fe66B18.5Cr5Co5 alloy can promote its crystallization from amorphous state and induce a grain refinement. The stronger the applied magnetic field, the lower the crystallization temperature. Holding the annealing time for 5 min, the crystallization occurs at 680 °C in conventional heat treatment, however, it happens at 650 °C when annealed with a 0.15 T field strength and 630 °C with a 0.25 T field strength. The maximum energy product for Nd5.5Fe66B18.5Cr5Co5 powder under optimum heat treatment with an applied magnetic field can increase about 17% because of the enhancement of exchange coupling role between the soft and hard phase due to the full crystallization and the grain size reduction.