Influence of Ni/Mn ratio on magnetostructural transformation and magnetocaloric effect in Ni48-xCo2Mn38+xSn12 (ax =0, 1.0, 1.5, 2.0,and 2.5) ferromagnetic shape memory alloys

摘要

An investigation on the magnetostructural transformation and magnetocaloric properties of Ni48-xCo2Mn38+xSn12 (x =0,1.0,1.5,2.0,and 2.5) ferromagnetic shape memory alloys is carried out.With the partial replacement of Ni by Mn in the Ni48Co2Mn38Sn12 alloy,the electron concentration decreases.As a result,the martensitic transformation temperature is decreased into the temperature window between the Curie-temperatures of austenite and martensite.Thus,the samples with x =1.5 and 2.0 exhibit the magnetostructural transformation between the weak-magnetization martensite and ferromagnetic austenite at room temperature.The structural transformation can be induced not only by the temperature,but also by the magnetic field.Accompanied by the magnetic-field-induced magnetostructural transformation,a considerable magnetocaloric effect is observed.With the increase of x,the maximum entropy change decreases,but the effective magnetic cooling capacity increases.