Site preferences of Fe2CoAl Heusler alloy: A first-principles DFT study (original) (raw)
Related papers
AIP Conference Proceedings, 2019
In this report, Fe2CoAl Heusler alloy is selected as a target to study site-preferences of atoms by first-principles calculations using WIEN2k code. It has been observed that Fe2CoAl (FCA) Alloy tend to form XA-I type structure (Hg2CuTi-type) which is energetically more favorable as compared to those of the others XA-II and XA-III structures. Further, we observed that the total magnetic moment per cell shows a strong dependence on-site preferences of Co in all available Wyckoff sites. However, this compound does not show a half-metallic character but a metallic behavior was observed for both spin direction at Fermi level (EF), still, it can be used as the spin-polarized material for spintronics application
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.
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.
Structural , magnetic , and magnetocaloric properties of intermetallic Fe 2 CoAl Heusler nanoalloy
2021
Spherical nanoparticles (NPs) made of intermetallic Fe2CoAl (FCA) Heusler alloy are synthesized via co-precipitation method and its structural, magnetic and magnetocaloric properties are explored, for the first time. The basic structural characterizations have revealed A2-disordered cubic Heusler structure. HRTEM with the SAED pattern analysis revealed crystalline nature of the FCA-NPs with a mean diameter of around 14 nm. Field and temperature dependent magnetization (M) study shows that the NPs are soft ferromagnetic with a high saturation magnetization (Ms) and Curie temperature (Tc). We also observed that FCA-NPs do not follow the Slater Pauling (SP) rule possibly because of the disorder present in this system. We further investigate its phase transition and magnetocaloric properties. The peak value of -∆SM vs T curve at a magnetic field change of 20 kOe corresponds to about 2.65 J/Kg-K, and the observed value of refrigeration capacity (RCP) was as large as 44 J/Kg, suggesting a...
Induced spin polarization in Fe2VAl by substitution of Co at Fe site
Computational Materials Science, 2015
The effects on electronic structure properties by Co substitution in Fe 2 VAl Heusler alloy have been determined by means of first principle calculations using generalized gradient approximation and calculated equilibrium lattice constants and magnetic moments for the series Fe 2Àx Co x VAl. The value of formation energy is minimized at the Fe (A, C) sites when Co substitutes at Fe, V and Al sites. The semi metallic behavior of Fe 2 VAl fades, while spin polarization is induced on Fe replaced by Co atom due to the influence of valence electrons of Co at the Fermi level. An enhancement of the total magnetic moment on increase in the Co content is observed due to the ferromagnetic coupling of Fe and Co atoms with V atoms at the B site and hybridization between Co-Co atoms at the A/C sites.
Ferrimagnetism and antiferro- magnetism in half-metallic Heusler alloys
physica status solidi (a), 2008
Half-metallic Heusler alloys are among the most promising materials for future applications in spintronic devices. Although most Heusler alloys are ferromagnets, ferrimagnetic or antiferromagnetic (also called fully-compensated ferrimagnetic) alloys would be more desirable for applications due to the lower external fields. Ferrimagnetism can be either found in perfect Heusler compounds or achieved through the creation of defects in ferromagnetic Heusler alloys.
Co 2 FeSi, a Heusler alloy with the highest magnetic moment per unit cell and the highest Curie temperature, has largely been described theoretically as a half-metal. This conclusion, however, disagrees with point contact Andreev reflection (PCAR) spectroscopy measurements, which give much lower values of spin polarization, P . Here, we present the spin polarization measurements of Co 2 FeSi by the PCAR technique, along with a thorough computational exploration, within the DFT and a GGA + U approach, of the Coulomb exchange U parameters for Co and Fe atoms, taking into account spin-orbit coupling. We find that the orbital contribution (m o ) to the total magnetic moment (m T ) is significant, since it is at least 3 times greater than the experimental uncertainty of m T . The account of m o radically affects the acceptable values of U. Specifically, we find no values of U that would simultaneously satisfy the experimental values of the magnetic moment and result in the half-metallicity of Co 2 FeSi. On the other hand, the ranges of U that we report as acceptable are compatible with spin polarization measurements (ours and the ones found in the literature), which all are within approximately the 40-60 % range. Thus, based on reconciling experimental and computational results, we conclude that (a) spin-orbit coupling cannot be neglected in calculating Co 2 FeSi magnetic properties, and (b) Co 2 FeSi Heusler alloy is not half-metallic. We believe that our approach can be applied to other Heusler alloys such as Co 2 FeAl.
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.
Journal of Magnetism and Magnetic Materials, 2011
Quaternary Heusler alloys Fe 1.5 M 0.5 CoSi with M ¼V, Cr, Mn and Fe have been investigated theoretically and experimentally. All of these samples crystallize in the ordered Heusler-type structure. The calculated electronic structure shows a pseudogap around E F in the minority spin states of Fe 2 CoSi. With the substitution of low-valent atoms for Fe, the majority antibonding peak is shifted to higher energy and a minority gap around the Fermi level is opened. High spin polarization ratio is obtained in Fe 1.5 M 0.5 CoSi (M ¼V, Cr, Mn) alloys. The calculated total spin moments decrease with decreasing number of valence electrons and follow the Slater-Pauling curve, which agree with the experimental results well. The Curie temperature decreases as M atom varies from Fe to V, but is always higher than 650 K, which is suitable for technical applications.