Grain oriented NiMnSn and NiMnIn Heusler alloys ribbons produced by melt spinning: Martensitic transformation and magnetic properties

We outline the microstructural, martensitic transformation and magnetic properties of Heusler alloys with starting compositions Ni50Mn37Sn13, Ni50Mn36In14, and Mn50Ni40In10, produced by melt spinning. The ribbons were obtained in argon environment at a high wheel linear speed of 48 m s−1 (typical dimensions: 1.2–2.0 mm in width, 4–12 mm in length, and 7–12 μm in thickness). EDS microanalysis showed that the resulting average elemental chemical composition is slightly shifted with respect to the starting one. Ribbons are fully crystalline and tend to show a highly ordered columnar-like microstructure with grains running through the entire ribbon thickness; the larger dimension of the grains is perpendicular to the ribbon plane. As-spun alloys were single-phase with ferromagnetic bcc L21 austenite as high-temperature parent phase. At low temperatures austenite transforms into a structurally modulated martensite with a lattice symmetry that depends on the system (7 M orthorhombic for Ni50Mn37Sn13, 10 M monoclinic for Ni50Mn36In14, and 14 M monoclinic for Mn50Ni40In10). Magnetization isotherms measured in the temperature interval where martensite thermally transforms into austenite confirmed the occurrence of field-induced reverse martensitic transition in the alloys studied.