Revealing essence of magnetostructural coupling of Ni-Co-Mn-Ti alloys by first-principles calculations and experimental verification

In this work,the effects of Co doping on the magnetostructural coupling transformation of Ni_(50-x)Co_(x)Mn_(50-y)Ti_(y)(x=0-15,y=12.5-15)Heusler alloys were systematically investigated through the first-princi-ples calculations and experimental verification.The cal-culation result indicates that the doped Co atoms prefer to occupy the Ni sublattice.The Co atoms tend to flock together in terms of the lowest energy principle.Since the formation energy of the austenite is higher than that of the martensite,the alloys will undergo martensitic transfor-mation for the Ni_(50-x)Co_(x)Mn_(37.5)Ti_(12.5)alloys(x=0-12.5).The magnetostructural coupling point of Ni_(50-x)Co_(x)Mn_(37.5)Ti_(12.5)alloys is predicted in the vicinity of x=11-12.Based on the computational composition Ni_(37.5)Co_(12.5)Mn_(37.5)Ti_(12.5),the Ni_(36)Co_(14)Mn_(36)Ti_(14)alloy with magnetostructural coupling near room temperature was experimentally developed by simultaneously increasing the Ti and Co contents.The largest magnetization change(ΔM)and magnetic entropy changes(ΔS_(m))obtained under magnetic field of 5 T for the martensitic transformation in the Ni_(36)Co_(14)Mn_(36)Ti_(14) alloy are about 87.6 A·m^(2)·kg^(-1)and 21 J·kg^(-1)·K^(-1),respectively.The fracture strength and strain for non-textured polycrystalline Ni_(36)Co_(14)Mn_(36)Ti_(14)alloy reach 953 MPa and 12.3%,respectively.The results show that the alloy not only possesses a large magne-tocaloric effect but also has excellent mechanical proper-ties.In addition,the 6 M modulated martensite is evidenced in the Ni-Co-Mn-Ti alloys via transmission electron microscopy technique.

Magnetostructural transformation and magnetocaloric effect in Mn_(48-x)V_xNi_(42)Sn_(10) ferromagnetic shape memory alloys

In this work, we tuned the magnetostructural transformation and the coupled magnetocaloric properties of Mn48-xVxNi42Sn10（x=0, 1, 2, and 3） ferromagnetic shape memory alloys prepared by means of partial replacement of Mn by V. It is observed that the martensitic transformation temperatures decrease with the increase of V content. The shift of the transition temperatures to lower temperatures driven by the applied field, the metamagnetic behavior, and the thermal hysteresis indicates the first-order nature for the magnetostructural transformation. The entropy changes with a magnetic field variation of 0-5 T are 15.2, 18.8, and 24.3 J.kg^-1.K^-1 for the x = 0, 1, and 2 samples, respectively. The tunable martensitic transformation temperature, enhanced field driving capacity, and large entropy change suggest that Mn48-xVxNi42Sn10 alloys have a potential for applications in magnetic cooling refrigeration.