Influence of mixing the low-valent transition metal atoms (Y, Y[sup (original) (raw)
We have calculated the electronic and magnetic properties of 3d transition metal based full Heusler compounds Co 2 CrZ (Z = Ga, Ge, As), by using full potential linearized augmented plane wave (FP-LAPW) method. The calculated density of states (DOS) and band structure for Co 2 CrZ shows the existence of band gap in their minority-spin channel. The respective energy gaps of Co 2 CrGe and Co 2 CrGa are 0.24 and 0.38 eV with their Fermi energies (E F s) lie exactly at the gap. The compound Co 2 CrAs when treated with local spin density approximation (LSDA) does not show half metallic ferromagnetism (HMF) even though there exist a gap this is because the E F does not lie at the middle of the gap. We have considered Co 2 CrAs as strongly correlated system as Cr-d states at E F are strongly localized thus the system was treated in terms of the LSDA + U. The total magnetic moment of Co 2 CrAs was found to be an exact integer value 5.00 l B within LSDA + U. We have also found that the total magnetic moments increase as the Z goes from Ga to As.
Physical Review Materials
In this paper we report an experimental study of structural, magnetic, and mechanical properties of quaternary Heusler alloys Co 2−x Y x FeSi (Y = Co, Fe, Mn, Cr, V, Ti, or Sc, 0 x 1) and the experimental findings are supported by ab initio electronic structure calculations. The alloys were synthesized using an arc-melting technique. Single phase microstructures are observed for all alloys substituted with low-valence transition metals Y except Sc. X-ray powder diffraction patterns at room temperature show the presence of Heusler-like face-centered cubic crystal structure in all single phase specimens. The low-temperature saturation magnetic moments, as determined from magnetization measurements, agree fairly well with our theoretical results and also follow the Slater-Pauling rule of thumb for half-metals, a prerequisite for half-metallicity. The alloys are predicted to exhibit half-metallic ferromagnetism by ab initio electronic structure calculations using the GGA+U approach. All stable compounds are observed to have high Curie temperatures with linear dependence with the valence electrons concentration in the alloys. Relatively high hardness values are also measured, approaching 15.7 GPa for Ti-substituted material, highest among the values reported for Heuslers so far. All these properties strongly suggest the alloys are promising for the spintronic applications at room temperature and above.
Theoretical Study of the Electronic and Thermodynamic Properties of Co2CrZ (Z=Ga,Al)
Universal journal of physics and application, 2018
The present work includes a first principle study of the electronic structure, elastic, magnetic and thermal properties of Co-based ternary full-Heusler alloys Co 2 CrX (x=Al,Ga). The lattice constant, bulk modulus, magnetic moment and density of states are studied using the full-potential linearized augmented plane wave method with the Generalized Gradient Approximation (GGA) as functional of exchange and correlation. This shows that the magnetic properties of the compound are dependent on electron concentration of main group element and all concentrations are magnetic in their equilibrium L2 1 structure. The calculations show that the alloys with all concentration are true half-metallic materials and exhibit 100% spin polarization at the Fermi level where it can be shifted within the energy-gap. In addition, the quasi-harmonic Debye model is applied to determine the thermal properties of the alloy.
Journal of Magnetism and Magnetic Materials, 2004
The effects of various substitutions on the electronic structure of Co in YðCo 1Àx M x Þ 2 compounds (M = Al, Si, Fe, Cu) are studied employing the coherent potential approximation as embodied in an all-electron TB-LMTO method. Two principal mechanisms affect the magnetic properties of Co as the impurity concentration increases: (i) a change of the 3d-electron concentration; (ii) effects of band smoothening due to disorder. The latter mechanism is dominant for Al and Si substitutions. Substituting 3d-element the former applies, but also disorder effects are present.
Physica B: Condensed Matter, 2012
The electronic structures of Co-based Heusler compounds CoTiAl 1À x Si x (x¼ 0, 0.25, 0.5, 0.75 and 1) are calculated by first-principles using the full potential linearized augmented plane wave (FP-LAPW) method within GGA and LSDAþU scheme. Particular emphasis was put on the role of the main group elements. In recent years, the GGA calculations of Co 2 TiAl (x¼ 0) and Co 2 TiSi (x¼ 1) indicated that they are half-metallic, but the electronic structure of this compound with x¼ 0.25, 0.5 and 0.75 has not been reported yet, neither theoretically nor experimentally. The calculated results reveal that these are half-metallic and exhibit an energy gap in the minority spin state and also show 100% spin polarization. The substitution of Al by Si leads to an increase in the number of valence electrons, with increasing x. Our calculated results clearly show that with the Si doping, the lattice parameter linearly decreases; bulk modulus increases, and the total magnetic moment increases. The calculated energy gap in the minority spin state, using GGA scheme, was smaller than that obtained by using LSDAþ U scheme. The outcomes of this research also show that the Co-3d DOS and therefore, the magnetic properties of compounds are dependent on electron concentration of the main group elements and it will affect the degree of p-d orbital occupation.