Magnetic properties and structural transformations in Ni–Co–Mn–Sn multifunctional alloys Original Research Article

A systematic study of the magnetic properties and both the temperature- and magnetic-field-induced structural transformations in the Ni50−xCoxMn39Sn11 (image) multifunctional alloys over a large temperature range from 500 K down to 10 K was performed. It is revealed that, with increasing x, the martensitic transformation temperatures first decrease slowly when image and then decrease rapidly when image; no martensitic transformation was observed in the alloys with image. The magnetic properties of these alloys are very sensitive to their chemical composition. The austenite in the alloys with image shows paramagnetic behavior and the martensite exhibits paramagnetic, superparamagnetic (SPM), and superspin glass (SSG) behaviors in different temperature ranges during cooling. In contrast, the austenite in the alloys with image is paramagnetic above its Curie temperature TC and ferromagnetic below TC, and the martensite shows SPM and SSG behaviors in different temperature ranges. The austenite in the alloys with image, which remains stable down to 10 K, shows paramagnetic and ferromagnetic behaviors above and below TC, respectively. The complete phase diagram for the Ni50−xCoxMn39Sn11 (image) alloy system, from high temperature down to 10 K, is established. A significant magnetic-field-induced decrease of martensitic transformation temperatures and almost fully reversible magnetic-field-induced structural transformation are achieved across a broad temperature range in the alloys with image. These results are important for understanding the composition and temperature-dependent functional properties, as well as their underlying mechanisms, in the Ni–(Co)–Mn–X (X = In, Sn, Sb) multifunctional alloys.