Half-Metallicity Of Ti₂-Based Heusler Alloys:A First-Principles Study

Spintronics is a new field of physics; it is different from traditional electronics. The electric charge and spin of the electrons as the carriers of information can be used in spintronics. In traditional electronics, electronic devices and semiconductor chips, the electric charge is used only, and the spin degree of the electron is not used, leading to limitations on the performance of electronic devices and computers. Comparing with the traditional electronic devices, spin electronics device is more stable, have stronger capacities of processing the data and characteristics of non-volatile. Half-metallic ferromagnets exhibit metatallic character in one of the spin band, while they are semiconductor in other spin band, i.e., there exists a band gap at the Fermi level, leading to spin polarization of100%. Because of the high spin polarization and high Curie temperature, much attention has been paid to Heusler alloys.In this thesis, we use full-potential linearized-augmented plane-wave (FLAPW) method based on density functional theory within the generalized gradient approximation (GGA) to investigate the electronic structure, magnetic properties, and half-metallicity of full-Heusler Ti2YAl (Y=V, Cr, Mn, Fe, Co, Ni, Cu, and Zn) alloys. Our studied results show that:(1) The total magnetic moments for the Ti2YAl (Y=Mn, Fe, Co, and Ni) alloys are integers, i.e.,01μB (Mn),1μB (Fe),2μB (Co),3μB (Ni). These total magnetic moments follow the Mt=Zt-18Slater-Pauling rule. The total magnetic moments for Ti2YAl (Y=V, Cr, Cu, and Zn) alloys are non-integers.(2) Ti2YAl (Y=Mn, Fe, Co, and Ni) alloys have band-gaps in the minority spin bands, and the Fermi level(EF)s are just located in the band-gaps, resulting in100%spin polarization. The calculated band-gaps of Ti2YAl (Y=Mn, Fe, Co, and Ni) alloys are0.358eV (Mn),0.330eV (Fe),0.486eV (Co), and0.281eV (Ni). Ti2MnAl alloy is a half-metallic antiferromagnet, and the Ti2YAl (Y=Fe, Co, and Ni) alloys are half-metallic ferrimagnets, whereas the Ti2YAl (Y=V, Cr, Cu, and Zn) alloys are conventional ferromagnets.(3) The origin of the band-gaps of Ti2YAl (Y=Mn, Fe, Co, and Ni) alloys are demonstrated to be mainly determined by the bonding t2and antibonding t2*states created from the hybridizations of the d states between the Ti (A)-Ti (B) coupling and Y atom.(4) For the non-uniform deformations along the [001] direction of Ti2YAl (Y=Mn, Fe, Co, and Ni) alloys, the alloys retain the half-metallicity in the deformation ranges of0.981<h/h0<1.013(Mn),0.969<h/h0<1.035(Fe),0.956<h/h0<1.052(Co), and0.955<h/h0<1.040(Ni).