Effects Of Doping Elements On Martensitic Transformation And Magnetic Properties In Ni-Mn-In Alloys

Ni-Mn-In based alloys are a kind of newly developed magnetic controlled functional material.Because of the strong magneto-structural coupling in these alloys,significant magnetocaloric effect can be realized under the external magnetic field.Thus,Ni-Mn-In alloys can be conceived as potential candidate materials for the magnetic refrigeration application.In fact,it is of great importance for magnetic refrigerants to have a large magnetocaloric effect in a wide temperature range.In this thesis,polycrystalline samples of Ni50-xMn36+xIn14(x=0,1,2,3,4),Ni49-xMn37In14Cox(x=1,2,3,4,5,6),Ni46Mn37-xIn14Co3Cux(x=1,2,3,4)and Ni45Co5Mn36.5In13.5-xGex(x=1,2,3,4)were prepared by arc melting process in argon atmosphere.The effect of composition on the martensitic transformation,the crystal structure,the microstructure and the magnetocaloric properties were systematically studied,which is expected to offer some guidelines for the further composition design and property improvement.For Ni49Mn37In14 alloy,its transformation temperature is near room temperature,and hysteresis is about 10 K.Under the field change of 5 T,the maximum magnetic entropy of 25.59 Jkg-1K-1 at 296 K,and the maximum magnetic entropy of-7.47 Jkg-1K-1 at 318 K are achieved,the total effective refrigerant capacity reached 276.14 Jkg-1.Under the field change of 1.5 T,the maximum adiabatic temperature is 2.37 K near the first-order transition,and-1.71 K near the second-order transition.For Ni48Mn37In14Co1 alloy,under the field change of 5 T,the difference of magnetization between the parent phase and the martensite phase is 88 emu/g,the maximum △SM of 13.63 Jkg-1K-1 and the effective refrigerant capacity RCeff of 263.06 Jkg-1 are achieved.Under the field change of 1.5 T,the maximum adiabatic temperature is 2.37 K at 254 K.Compared with Ni49Mn37In14 alloy,the difference of magnetization between the parent phase and the martensite phase increases,the change in martensitic transformation temperature induced by magnetic field decreases.For Ni46Mn37-xIn14Co3Cux(x=1,2,3,4)alloys,with the increase of Cu content,the martensitic transformation temperature gradually increased,the Curie transition temperature decreased gradually,and the hysteresis decreased.The addition of Cu element can effectively improve the △SM,RC and RCeff of the alloys,and the magnetocaloric effect increased.Under the field change of 5 T,the maximum magnetic entropy of Ni46Mn35In14Co3Cu2 alloy is 17.95 Jkg-1K-1 and the effctive refrigerant capacity reached 288.44 Jkg-1.Under the field change of 1.5 T,the maximum adiabatic temperature of Ni46Mn35In14Co3Cu2 alloy is 5.14 K at 272 K near the martensitic transformation.For Ni45Co5Mn36.5In13.5-xGex(x=1,2,3,4)alloys,with the gradual increase of Ge content,martensitic transformation temperature gradually increased,Curie transition temperature gradually decreased,and the hysteresis decreased.Under the field change of 5 T,the effective refrigerant capacity of Ni45Co5Mn36.5In11.5Ge2 alloy reached 331.93 Jkg-1.Under the field change of 1.5 T,the maximum adiabatic temperature change decreases with the increase of Ge content,the maximum adiabatic temperature of Ni45Co5Mn36.5In12.5Ge1 alloy is 3.86 K at 254 K near the martensitic transformation.