Effects of 1 at.% additions of Co, Fe, Cu, and Cr on the properties of Ni-Mn-Ga-based magnetic shape memory alloys

The effect of Mn substitution with 1 at.% additions of Co, Fe, Cu, and Cr on the properties of a polycrystalline Ni49.8Mn28.5Ga21.7 magnetic shape memory (MSM) alloy after heat-treatment is examined. Doped alloys exhibit a single-phase five-layered modulated martensite structure at ambient temperature and a slight increase in martensite transformation temperatures compared to the non-doped alloy, without a substantial alteration of the Curie temperature. Cr addition decreases the grain size, while additions of Co, Fe, and Cu increase the grain size, as compared to the non-doped alloy. Particularly, Co addition leads to extreme grain growth, transforming the grain structure from polycrystalline to oligocrystalline with an average grain diameter of 2.83 mm. The Co-doped alloy demonstrates an MSM effect with a low switching field of H<0.15 T and a twinning stress of 1 MPa, which is a promising composition for use in polycrystalline-based MSM research and applications.