Effect of L21 and XA ordering on phase stability, half-metallicity and magnetism of Co2FeAl Heusler Alloy: GGA and GGA+U approach (original) (raw)
Related papers
First-Principles Investigation of the L21 and XA Ordering Competition in Co2FeAl Heusler Alloy
AIP Conference Proceedings , 2019
Co2FeAl Heusler alloy was selected as a target to study L21 and XA ordering of atoms by first-principles calculations using WIEN2k code. It has been observed that Co2FeAl (CFA) Alloy tend to form L21 type structure, which is more energetically favorable and much stable compared to XA type structure. Further, we observed that the total magnetic moment (Mt) shows a strong dependence on site preferences of Fe in all available Wyckoff sites. However, this compound does not show a half-metallic character in both types of ordered structures still, it can be used as the spin-polarized material for spintronics application. Our results are opposite to usual site preference rule and approving the validity of the Slater-Pauling rule.
Journal of Physics: Condensed Matter, 2020
Density functional theory calculations within the generalized gradient approximation are employed to study the ground state of Co2FeAl. Various magnetic configurations are considered to find out its most stable phase. The ferromagnetic ground state of the Co2FeAl is energetically observed with an optimized lattice constant of 5.70 Å. Thereafter, the system was subjected under uniform and non-uniform strains to see their effects on spin polarization (P) and half-metallicity. The effect of spin orbit coupling is considered in the present study. Half-metallicity (and 100 % P) is only retained under uniform strains started from 0 to +4%, and dropped rapidly from 90% to 16% for the negative strains started from-1% to-6%. We find that the present system is much sensitive under tetragonal distortions as half-metallicity (and 100% P) is preserved only for the cubic case. The main reason for the loss of half-metallicity is due to the shift of the bands with respect to the Fermi level. We also discuss the influence of these results on spintronics devices.
Ab initio studies of Co2FeAl1−xSix Heusler alloys
Journal of Magnetism and Magnetic Materials, 2016
We present results of extensive theoretical studies of Co2FeAl1−xSix Heusler alloys, which have been performed in the framework of density functional theory employing the all-electron fullpotential linearized augmented plane-wave scheme. It is shown that the Si-rich alloys are more resistive to structural disorder and as a consequence Si stabilizes the L21 structure. Si alloying changes position of the Fermi level, pushing it into the gap of the minority spin-band. It is also shown that the hyperfine field on Co nuclei increases with the Si concentration, and this increase originates mostly from the changes in the electronic density of the valence electrons.
Substituting the main group element in cobalt–iron based Heusler alloys: Co2FeAl1− xSix
This work reports about electronic structure calculations for the Heusler compound Co 2 FeAl 1−x Six. Particular emphasis was put on the role of the main group element in this compound. The substitution of Al by Si leads to an increase of the number of valence electrons with increasing Si content and may be seen as electron-doping. Self-consistent electronic structure calculations were performed to investigate the consequences of the electron doping for the magnetic properties. The series Co 2 FeAl 1−x Six is found to exhibit half-metallic ferromagnetism and the magnetic moment follows the Slater-Pauling rule. It is shown that the electron-doping stabilises the gap in the minority states for x = 0.5.
arXiv: Materials Science, 2020
Experimental and computational studies were performed on Co2FeGe Heusler alloy. It was found that the alloy has very high experimental magnetic moment of 6.1 muB/f.u., curie temperature of 1073K and very high spin-wave stiffness constant of 10.4 nm2-meV, which indicates that the magnetic moment is very high and do not vary with change in temperature in the range 0-300K. The alloy strictly follows Slater-Pauling (SP) rule and the minor experimental deviation from its SP value is justified by doing full-potential density functional calculations which gives more accurate result when electron-electron correlation parameter (U) is taken into account with conventional GGA method. Effect of lattice strain and electron correlation on individual atomic moments, total magnetic moment and spin-polarization is studied in detail and can be concluded that they have a role in the deviation of the experimental results from the expected theoretical values.
Competition of L2 1 and XA ordering in Fe 2 CoAl Heusler alloy: a first-principles study
THE EUROPEAN PHYSICAL JOURNAL B, 2020
The physical properties of Fe2CoAl (FCA) Heusler alloy are systematically investigated using the Q1 first-principles calculations within generalized gradient approximation (GGA) and GGA+U. The influence of atomic ordering with respect to the Wyckoff sites on the phase stability, magnetism and half metallicity in both the conventional L21 and XA phases of FCA is focused in this study. Various possible hypothetical structures viz., L21, XA-I, and XA-II are prepared by altering atomic occupancies at their Wyckoff sites. At first, we have determined the stable phase of FCA considering various non-magnetic (or paramagnetic), ferromagnetic (FM) and antiferromagnetic (AFM) configurations. Out of these, the ferromagnetic (FM) XA-I structure is found to be energetically most stable. The total magnetic moments per cell are not in agreement with the Slater-Pauling (SP) rule in any phase; therefore, the half-metallicity is not observed in any configurations. However, FM ordered XA-I type FCA shows 78% spin polarization at EF. Interestingly, the results of XA-I type FCA are closely matched with the experimental results.
Physica B: Condensed Matter, 2015
We investigate the effect of the substitution of Co with Fe on the structural, electronic and magnetic properties of a series of quaternary Co 2 À x Fe x CrAl Heusler alloys. The alloy orders in the B2 structure for composition of x Z0.4. The half metallicity in the parent Co 2 CrAl is retained in the whole series of alloys on partial substitution of Co with Fe atoms. DC magnetization studies evidence a linear increase in saturation magnetization and Curie temperature increase in Fe content. Mössbauer spectra show that along the series the average hyperfine field and combined relative area under the curve of sextets increase linearly with increase in Fe content corroborating results obtained from DC magnetization studies.
A comparative study of a Heusler alloy Co2FeGe using LSDA and LSDAþU
We have calculated the on-site Coulomb repulsion (U) for the transition elements Co and Fe. To study the impact of Hubbard potential or on-site Coulomb repulsion (U) on structural and electronic properties the calculated values of U were added on GGA and LSDA. We performed the structure optimization of Co 2 FeGe based on the generalized gradient approximation (GGA and GGA þU). The calculation of electronic structure was based on the full potential linear augmented plane wave (FP-LAPW) method and local spin density approximation (LSDA) as well as exchange correlation LSDA þU. The Heusler alloy Co 2 FeGe fails to give the half-metallic ferromagnetism (HMF) when treated with LSDA. The LSDA þU gives a good result to prove that Co 2 FeGe is a HMF with a large gap of 1.10 eV and the Fermi energy (E F ) lies at the middle of the gap of minority spin. The calculated density of states (DOS) and band structure show that Co 2 FeGe is a HMF when treated with LSDA þ U.
Ab initio density functional calculations are performed on the Co3−xFexSi alloys with variable iron composition (1 ≤ x ≤ 3). The evolution of the structural, electronic, and magnetic properties is investigated within different levels of approximations. These alloys crystallize in cubic Heusler structures, which evolve from the regular L21 structure for Co2FeSi to the inverse X structure for x ≥ 2. Using on-site Coulomb interactions of Ueff(Co) = 3.07 eV and Ueff(Fe) = 3.4 eV is found to describe consistently the experimental properties for x ≤ 2. A good agreement between calculated and experimental magnetic moments is found for the cubic inverse Heusler phases without the addition of Hubbard-model. The spin polarization is found to range from 1 for Fe concentrations of x ≤ 2, indicating the half-metallic character, to −0.29 at x = 3.