Effect of cobalt doping on martensitic transformations and the magnetic properties of Ni50−xCoxMn37Sn13 (x = 1, 2, 3) Heusler ribbons

Abstract

The effect of cobalt doping on martensitic transformations and the magnetic properties of Ni50−xCox Mn37Sn13 (x = 1, 2, 3) magnetic shape memory alloys obtained by melt spinning in the form of ribbons is studied. The crystallographic structure of all of the ribbons at room temperature is austenite cubic L21. SEM micrographs indicate the formation of textured ribbons with columnar grains growing up perpendicular to the ribbon plane. For all of the ribbons, DSC cyclic scans reveal the martensitic transformation on cooling and the reverse austenitic transformation upon heating below room temperature. In addition, they indicate that the martensitic transformation temperatures decrease with an increasing cobalt content.Thermomagnetic curves reveal the coexistence of AFM and FM exchange interactions at low temperatures. Likewise, the magnetization change (ΔM) between the martensite and austenite phase, as well as the austenite Curie temperature (TCA), increase with increasing cobalt content in the ribbons. Structural transformations are also sensitive to the external applied magnetic field. This fact suggests that the structural transformation temperatures of the ribbons could be tuned to the desired functional temperature by controlling the cobalt amount through the replacement of Ni as well as by changing the applied magnetic field, which could lead to an enhancement of the magnetic properties.