Magnetic coercivity control by heat treatment in Heusler Ni–Mn–Ga(–B) single crystals

The combination of enlarged magnetic coercivity and magnetic shape memory (MSM) functionality is essential for novel magnetomechanical effects in MSM alloys. We found that increasing the density of thermal antiphase boundaries (APBs) provides a method to increase the magnetic coercivity without deteriorating the MSM functionality. APB density was controlled by different heat treatments in Ni–Mn–Ga (–B) MSM single crystals with five-layered modulated martensite structure. Slow cooling ∼1 K/min of Ni–Mn–Ga through the B2′–L21 transition resulted in a low density ( 1/micrometer) of APBs observed by magnetic force microscopy and low coercivity