Zn掺杂对Heusler型磁性形状记忆合金Ni_(2)FeGa_(1-x)Zn_(x)(x=0-1)电子结构、磁性与马氏体相变影响的第一性原理研究

First-principle study on effects of Zn-doping on electronic structure,magnetism and martensitic transformation of Heusler type MSMAs Ni_(2)FeGa_(1-x)Zn_(x)(x=0-1)

通过第一性原理计算研究了Zn掺杂对典型磁性形状记忆合金Ni_(2)FeGa的电子结构、马氏体相变和磁性的影响.在Ni_(2)FeGa_(1-x)Zn_(x)(x=0,0.25,0.5,0.75,1)中,取代Ga的Zn原子更倾向于占据Heusler合金晶格的D位.计算表明Ni_(2)FeGa_(1-x)Zn_(x)合金马氏体和奥氏体相之间的能量差DEM随着Zn掺杂量的增加而不断增大,这有助于增加Ni_(2)FeGa_(1-x)Zn_(x)马氏体相的稳定性并提高马氏体相变温度TM,这一规律与材料态密度中的Jahn-Teller效应密切相关.与此同时,Zn的掺杂没有改变这些合金的磁结构,Ni_(2)FeGa_(1-x)Zn_(x)合金中Ni,Fe原子磁矩始终为铁磁性耦合.形成能Ef的计算表明,Zn掺杂会导致Ef略有增大,但在整个研究的范围内形成能Ef始终保持为负值.另外,Zn掺杂对Ni_(2)FeGa的Heusler L2_(1)相有稳定作用,有助于抑制面心结构L1_(2)相的产生.

The magnetic shape memory alloys(MSMAs)have both martensitic transformation and ferromagnetism in the same material,thus external magnetic field can be used to induce/control the phase transformation or the reorientation of martensite variant.MSMAs have received considerable attention for their interesting properties and wide applications in different fields.For practical applications,the martensitic transformation temperature TM is an important factor and a high TM is preferable.Recently,Zn-doping has been found to be a possible way to elevate the value of TM of Ni-Mn based MSMA,but this effect on other kinds of MSMAs is not very clear yet.Heusler alloy Ni_(2)FeGa is a typical MSMA with unique properties,however,its TM is relatively low.So it can be meaningful to find possible ways to increase its phase transition temperature.In this paper,the influences of Zn-doping on the electronic structure,martensitic transformation and magnetic properties of Heusler-type magnetic shape memory alloy Ni_(2)FeGa are investigated by first-principle calculations.Total energy calculation and charge density difference indicate that Zn atom prefers to occupy the Ga(D)site when substituting for Ga in Ni_(2)FeGa_(1-x)Zn_(x)(x=0,0.25,0.5,0.75,1).This main-group-element-like behavior is related to the closed 3d shell of Zn.Due to the similar atomic radii of Ga and Zn,Zn-doping does not lead the lattice constant to change greatly.The variation of the energy difference DEM between the martensite and austenite with Zn content increasing is calculated,and the result shows that DEM increases with Zn-doping increasing,and thus conducing to increasing the stability of the martensite phase and to evaluating the transformation temperature TM in Ni_(2)FeGa_(1-x)Zn_(x).This trend can be explained by the Jahn-Teller effect observed in the DOS structure.The Zn-doping does not change the magnetic structure of Ni_(2)FeGa.A ferromagnetic coupling between Fe spin moment and Ni spin moment can be observed within the whole range studied.The calculated total spin moment increases with Zn content increasing.The variation of formation energy Ef with Zn-doping is investigated.In Ni_(2)FeGa_(1-x)Zn_(x) a negative Ef is retained within the whole range studied,though it increases slightly with the doping of Zn.It is also found that the Zn-doping can increase the stability of L2_(1) Heusler phase in Ni_(2)FeGa_(1-x)Zn_(x) and suppress the formation of the FCC L1_(2) phase.