Physical Properties Of CoFe-Based Heusler Alloys

Heusler alloys present plentyful physical properties. In recent years, it has been found that some alloys with ferromagnetic shape memory effect and half-metallic. Due to these prominent properties, these alloys have a great application prospect and become a hotspot of current researches. We concentrate on following aspects:(a) Co50Fe25-xMnxSi25 alloys which exhibit half-metalic have been studied in experiment and theory. Generalized Gradient Approximation (GGA) considering the coulomb interaction (GGA+U) based on density functional theory (DFT) has been adopted in the first principle calculation. Compared with the experiment results, the crystal structure, magnetic, moment and half-metallic of these alloys has been investigated.(b) The second part mainly discusses properties of Co50-xFe50+xSi25 alloys in theory. The first principle calculation method is generalized gradient approximation (GGA) considering the coulomb interaction among the electrons (GGA+U) based on density functional theory (DFT). It has been found that these alloys are ferromagnetic and their moment linearly decreased with the increase of Fe content. Meanwhile, considering the Fermi energy of Fe2CoSi alloy is in the bottom of conduction band and the Fermi energy of Co2FeSi alloy is in the top of valence band, we has investigated the half-metallic of Co50-xFe50+xSi25 alloys.(c) Co2FeGa alloy is similar to Co2FeSi alloy which exhibit the highest Curie temperature, and the largest saturation moment. Saturation moment of Co2FeGa alloy is 5.03μB and 5.13μB for Fe2CoGa alloy. We study variation of the crystal structure, saturation moment and electronic structure of Co50-xFe25+xGa25 alloys with the increase of Fe content, through the KKR-CPA-LDA and CASTEP-LDA primary principles calculation method. It has been found that variation of the saturation moment is parabolic which is a attractive point.(d) CoFe alloy is known as the transition metal binary alloys with largest saturation moment, coercive force and so on. Its ferromagnetic and ordering phase transition have been reported in many previous studies. Conbine experiment with first principle calculation, we studies magnetic phase transition, ferromagnetic and curie temperature of Co50Fe50-xSix alloys which transform from B2 structure CoFe alloy to L21 structure Co2FeSi Heusler alloy with the increase of Si content.