First-principles And Experimental Study Of Ti Doping Ni-Mn-Ga Alloy

Ni-Mn-Ga alloy has a great development potential due to the thermoelastic and magnetic shape memory effects, it has attracted much attention in the research of new intelligent materials. In this paper, tetragonal distortions,martensitic transformation and phase stability of stoichiometric Ni₈Mn₄Ga₄ and Ni₉Mn₄Ga₃ alloys have been studied by first-principle method. In the process of tetragonal distortions, the volume of the supercell keeps constant, the relationship between the total energy difference??E??corresponding to L21phase? and ac show that Ni₈Mn₄Ga₄ has one stable martensite phase at ac=275.1, Ni₉Mn₄Ga₃ at ac=940.0 and ac=325.1, respectively. When one Ga atom replaced by a Ni atom, the volume of Ni₉Mn₄Ga₃ is reduced, the total magnetic moment increases slightly, the TM has improved, and the stability of the system decreases.The effect of Ti content on lattice parameters, total magnetic moment,martensitic transformation temperature and phase stability of Ni₉Mn₄Ga_3-xTi_x?x=0, 0.5, 1, 2? alloy have been studied by first-principle method, when the electron spin has been considered in calculation. The results of formation energy and distortion energy indicate that the doped Ti prefers to occupy the Ga sites in Ni₉Mn₄Ga₃ alloy. The distance of Ni-Mn increased and the number of Ga atoms in the system decreases with the increasing Ti content, which weakens the exchange coupling between Mn atoms, which reduce the total magnetic moment.The energy difference??E? between austenitic and martensitic and ac increase with Ti content, the TM thereupon rising. The stability of ferromagnetic martensite phase of Ni₉Mn₄Ga_3-xTi_x?x=0, 0.5, 1, 2? alloys enhances with the increasing x value.In addition to the theoretical calculation, the ribbons of Ni₈Mn₄Ga₄,Ni₉Mn₄Ga₃ and Ni9Mn4Ga2 Ti alloy have been prepared by melt-spinning method, the crystal structure at room temperature and magnetic properties of samples have been tested and analyzed. The component have a great influence on crystal structure, TM and magnetic properties of ribbons. The Ni₈Mn₄Ga₄ ribbons have ferromagnetic austenitic phase, a apparent parallel magnetic anisotropy, belong to low-temperature shape memory alloys; the Ni₉Mn₄Ga₃ and Ni9Mn4Ga2 Ti ribbons have paramagnanetic martensitic phase at room-temperature, a weaker magnetic anisotropy, belong to high-temperature shape memory alloys. The martensitic transformation of Ni₈Mn₄Ga₄, Ni₉Mn₄Ga₃ and Ni9Mn4Ga2Ti alloys maintain one-step thermoelastic, and the TM increased successively. The ferromagnetic and magnetic properties of Ni₉Mn₄Ga₃ ribbons become more and more strengthen with the decreasing testing temperature.