Effects of high magnetic field on the reactive sintering process of Mn–Ga magnetic composites

Abstract

This study focuses on the microstructure and magnetic properties of Mn-20at. %Ga composites prepared via high-energy ball milling and subsequent reactive sintering under a high magnetic field (HMF). XRD identified the ɛ-Mn3Ga, β-Mn0.85Ga0.15, and α-Mn phases, and their fractions determined the magnetic properties of the composites. The results revealed that HMF enhanced the fractions of both ɛ-Mn3Ga and β-Mn0.85Ga0.15 phases and decreased the fraction of α-Mn. The magnetic-field-induced enhancement effect on the reaction was mainly due to a decrease in the activation energy, which mainly affected the phase reaction at the initial stages. However, a HMF of 9–12 T suppressed the atomic diffusion between Mn and Ga, reducing the reaction-enhancing effect of the magnetic field. Compared with zero-field annealing, the 3 T in-field annealing enhanced the remanence and coercivity of the composite by 44% and 16%, respectively. In contrast, the 12 T HMF decreased the remanence but increased the coercivity to its highest value. The coercivity of the 12 T in-field samples reaches 11.09 kOe after 8 h of in-field annealing. After the in-field annealing, subsequent zero-field annealing for an appropriate duration may further increase the remanence and energy product. Enhancing the in-field annealing temperature up to 400 °C may increase the coercivity but decrease the remanence considerably.