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

Abstract A systematic study of the magnetic properties and both the temperature- and magnetic-field-induced structural transformations in the Ni 50− x Co x Mn 39 Sn 11 ( 0 ⩽ x ⩽ 10 ) 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 0 ⩽ x ⩽ 4 and then decrease rapidly when 5 ⩽ x ⩽ 8 ; no martensitic transformation was observed in the alloys with 9 ⩽ x ⩽ 10 . The magnetic properties of these alloys are very sensitive to their chemical composition. The austenite in the alloys with 0 ⩽ x ⩽ 4 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 5 ⩽ x ⩽ 8 is paramagnetic above its Curie temperature T C and ferromagnetic below T C , and the martensite shows SPM and SSG behaviors in different temperature ranges. The austenite in the alloys with 9 ⩽ x ⩽ 10 , which remains stable down to 10 K, shows paramagnetic and ferromagnetic behaviors above and below T C , respectively. The complete phase diagram for the Ni 50− x Co x Mn 39 Sn 11 ( 0 ⩽ x ⩽ 10 ) 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 5 ⩽ x ⩽ 8 . 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.