Understanding the strain effect on coercivity enhancement in L1-Mn56Ga42 alloy via low-energy mechanical cryomilling

Abstract Varying degrees of strain were observed in L10-Mn56Ga42 powders via low-energy mechanical cryomilling, and the relationship between coercivity and strain was analyzed in detail. With increasing milling time, the powders do not show obvious variations in grain size and cell parameters, but a large strain is induced into the powders, leading to a remarkable enhancement in coercivity. A maximum coercivity of up to 6.7 kOe was accomplished for 20 h milled powders, with a high residual strain of about 0.96%. The initial magnetization curve indicates that the coercivity mechanism is mainly governed by the domain-wall pinning process where strain-induced defects act as pinning centers. Studies on heat treatments show that the strain-induced coercivity contributes to over 50% of the total coercivity, and a moderate annealing can eliminate the strain, changing the coercivity mechanism to a nucleation process.