Electronic structure, optical and magnetic properties of Co2FeGe Heusler alloy films
TL;DR: In this paper, the optical properties of a half-metallic full-Heusler Co2FeGe alloy were investigated experimentally and theoretically, and first principles calculations of the electronic structure and the dielectric tensor were performed using the fullpotential linearized-augmented-plane-wave method.
Abstract: Optical properties of ferromagnetic half-metallic full-Heusler Co2FeGe alloy are investigated experimentally and theoretically. Co2FeGe thin films were obtained by DC magnetron sputtering and show the saturation magnetization at T = 10 K of m≈5.6μB/f.u., close to the value predicted by the Slater-Pauling rule. First-principles calculations of the electronic structure and the dielectric tensor are performed using the full-potential linearized-augmented-plane-wave method in the generalized gradient approximation (GGA) and GGA + U approximation. The measured interband optical conductivity spectrum for the alloy exhibits a strong absorption band in the 1–4 eV energy range with pronounced fine structure, which agrees well with the calculated half-metallic spectrum of the system, suggesting a near perfect spin-polarization in the material.
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TL;DR: In this article, structural, magnetic and electronic properties of stoichiometric Co2 YZ Heusler alloys have been studied by means of ab initio calculations and Monte Carlo simulations.
Abstract: Structural, magnetic and electronic properties of stoichiometric Co2 YZ Heusler alloys (Y = Cr, Fe, Mn and Z = Al, Si, Ge) have been studied by means of ab initio calculations and Monte Carlo simulations. The investigations were performed in dependence on different levels of approximations in DFT (FP and ASA modes, as well as GGA and GGA + U schemes) and external pressure. It is shown that in the case of the GGA scheme the half-metallic behavior is clearly observed for compounds containing Cr and Mn transition metals, while Co2FeZ alloys demonstrate the pseudo half-metallic behavior. It is demonstrated that an applied pressure and an account of Coulomb repulsion (U) lead to the stabilization of the half-metallic nature for Co2 YZ alloys. The strongest ferromagnetic inter-sublattice (Co–Y) interactions together with intra-sublattice (Co–Co and Y–Y) interactions explain the high values of the Curie temperature obtained by Monte Carlo simulations using the Heisenberg model. It is observed that a decrease in valence electrons of Y atoms (i.e. Fe substitution by Mn and Cr) leads to the weakening of the exchange interactions and to the reduction of the Curie temperature. Besides, in the case of the FP mode Curie temperatures were found in a good agreement with available experimental and theoretical data, where the latter were obtained by applying the empirical relation between the Curie temperature and the total magnetic moment.
43 citations
TL;DR: In this article, the authors explore the possibility of large magnetocrystalline anisotropy energies in Heusler compounds that are unstable with respect to a tetragonal distortion.
Abstract: With a view to the design of hard magnets without rare earths we explore the possibility of large magnetocrystalline anisotropy energies in Heusler compounds that are unstable with respect to a tetragonal distortion. We consider the Heusler compounds Fe2YZ with Y = (Ni, Co, Pt), and Co2YZ with Y = (Ni, Fe, Pt) where, in both cases, Z = (Al, Ga, Ge, In, Sn). We find that for the Co2NiZ, Co2PtZ, and Fe2PtZ families the cubic phase is always, at T = 0, unstable with respect to a tetragonal distortion, while, in contrast, for the Fe2NiZ and Fe2CoZ families this is the case for only 2 compounds—Fe2NiGe and Fe2NiSn. For all compounds in which a tetragonal distortion occurs we calculate the magnetocrystalline anisotropy energy (MAE) finding remarkably large values for the Pt containing Heuslers, but also large values for a number of the other compounds (e.g. Co2NiGa has an MAE of −2.38 MJ m−3). The tendency to a tetragonal distortion we find to be strongly correlated with a high density of states (DOS) at the Fermi level in the cubic phase. As a corollary to this fact we observe that upon doping compounds for which the cubic structure is stable such that the Fermi level enters a region of high DOS, a tetragonal distortion is induced and a correspondingly large value of the MAE is then observed.
32 citations
TL;DR: The full potential linearized augmented plane wave method with the generalized gradient approximation (FPLAPW-GGA) has been used to understand the electronic, magnetic, optical and elastic properties of Cu2MnAl a full-Heusler compound as mentioned in this paper.
23 citations
TL;DR: In this paper, the structural, magnetic and electronic properties of the Co2FeGe1−x 1.5Si0.5, 1) Heusler compounds have been calculated using the full-potential linearized augmented plane-wave method within the spin density functional theory within the generalized gradient approximation of Perdew-Burke-Ernzerhof.
Abstract: In this study, the structural, magnetic and electronic properties of the Co2FeGe1−x
Si
x
(x = 0, 0.5, 1) Heusler compounds have been calculated using the full-potential linearized augmented plane-wave method based on the spin density functional theory within the generalized gradient approximation of Perdew-Burke-Ernzerhof. In order to take into account the correlation effects, we have also performed GGA + U calculations, where the Hubbard on-site Coulomb interaction correction U is calculated by using the constraint local density approximation for the Co and the Mn atoms. The Cu2MnAl-type structure is found to be energetically more favorable than the Hg2CuTitype structure for both the Co2FeSi and the Co2FeGe compounds. The calculated atomic resolved densities of states of Co2FeSi and Co2FeGe indicate nearly half-metallic behaviors with small spindown electronic densities of states at the Fermi level. This behavior is corrected by including the Hubbard Coulomb energy U term. The Coulomb exchange correlation U confirms the halfmetallic property in both the Co2FeSi and the Co2FeGe compounds. We also discuss the electronic structures, the total and the partial densities of states, and the local magnetic moments. The Co2FeGe0.5Si0.5 compound shows a nearly half-metallic behavior with a small spin-down electronic density of states at the Fermi level in both the GGA and GGA+U approximations.
23 citations
TL;DR: In this article, the effect of disorder on electronic, magnetic, and optical properties of Co2CrZ (Z = Al, Si, Ga, Ge) Heusler alloy using density functional theory is presented.
Abstract: This paper presents the effect of disorder on electronic, magnetic, and optical properties of Co2CrZ (Z = Al, Si, Ga, Ge) Heusler alloy using density functional theory. Binary mixing is the most common form of atomic disorder in these compounds. We have considered three types of disorders: DO
3, A2, and B2 disorder which corresponds to X-Y, X-Z, and Y-Z mixing, respectively. After structural optimization, we found that A2 disorder has high formation energy and is most unlikely to occur. The half-metallic nature of the alloy is destroyed in the presence of DO
3 and A2 disorder. The destruction of half-metallicity is due to reconstruction of energy states. B2 disorder retains the half-metallic nature of the alloy but spin-polarization value is reduced slightly as compared to the ordered alloy. In addition, the optical properties such as dielectric function, refractive index, absorption spectra, optical conductivity, reflectivity, and energy loss function of these alloys have also been investigated.
20 citations
References
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TL;DR: A simple derivation of a simple GGA is presented, in which all parameters (other than those in LSD) are fundamental constants, and only general features of the detailed construction underlying the Perdew-Wang 1991 (PW91) GGA are invoked.
Abstract: Generalized gradient approximations (GGA’s) for the exchange-correlation energy improve upon the local spin density (LSD) description of atoms, molecules, and solids. We present a simple derivation of a simple GGA, in which all parameters (other than those in LSD) are fundamental constants. Only general features of the detailed construction underlying the Perdew-Wang 1991 (PW91) GGA are invoked. Improvements over PW91 include an accurate description of the linear response of the uniform electron gas, correct behavior under uniform scaling, and a smoother potential. [S0031-9007(96)01479-2] PACS numbers: 71.15.Mb, 71.45.Gm Kohn-Sham density functional theory [1,2] is widely used for self-consistent-field electronic structure calculations of the ground-state properties of atoms, molecules, and solids. In this theory, only the exchange-correlation energy EXC › EX 1 EC as a functional of the electron spin densities n"srd and n#srd must be approximated. The most popular functionals have a form appropriate for slowly varying densities: the local spin density (LSD) approximation Z d 3 rn e unif
146,533 citations
IBM1
TL;DR: Heusler compounds as discussed by the authors are a remarkable class of intermetallic materials with 1:1:1 or 2:1-1 composition comprising more than 1500 members, and their properties can easily be predicted by the valence electron count.
1,675 citations
TL;DR: In this article, the authors generalized the linearized-augmented-plane-wave (LAPW) method for thin films by removing the remaining shape approximation to the potential inside the atomic spheres, and implemented a new technique for solving Poisson's equation for a general charge density and potential is described and implemented in the film LAPW method.
Abstract: The linearized-augmented-plane-wave (LAPW) method for thin films is generalized by removing the remaining shape approximation to the potential inside the atomic spheres. A new technique for solving Poisson's equation for a general charge density and potential is described and implemented in the film LAPW method. In the resulting full-potential LAPW method (FLAPW), all contributions to the potential are completely taken into account in the Hamiltonian matrix elements. The accuracy of the method---already well known for clean metal surfaces---is demonstrated for the case of a nearly free (noninteracting) ${\mathrm{O}}_{2}$ molecule which is a severe test case of the method because of its large anisotropic charge distribution. Detailed comparisons show that the accuracy of the FLAPW results for ${\mathrm{O}}_{2}$ exceeds that of existing state-of-the-art local-density linear-combination-of-atomic-orbitals (LCAO)-type calculations, and that taking the full potential LAPW results as a reference, the LCAO basis can be improved by adding off-site functions. Thus the full-potential LAPW is a unified method which is ideally suited to test not only molecular adsorption on surfaces, but also the components of the same system separately, i.e., the extreme limits of the molecule and the clean surface.
1,459 citations
TL;DR: In this article, the magneto-optical Kerr rotation in more than 200 metallic systems comprising alloys as well as intermetallic compounds of 3D transition metals was studied and the saturation moment at 4.2 K was determined.
686 citations
TL;DR: In this paper, results of ab initio band structure calculations for A2BC Heusler compounds that have A and B sites occupied by transition metals and C by a main group element are presented.
Abstract: In this paper, results of ab initio band structure calculations for A2BC Heusler compounds that have A and B sites occupied by transition metals and C by a main group element are presented. This class of materials includes some interesting half-metallic and ferromagnetic properties. The calculations have been performed in order to understand the properties of the minority band gap, the peculiar transport properties and magnetic behaviour found in these materials. Among the interesting aspects of the electronic structure of the materials are the contributions from both A and B atoms to the total magnetic moment. The magnitude of the total magnetic moment shows a trend consistent with the Slater–Pauling type behaviour in several classes of these compounds. The total magnetic moment also depends on the kind of C atoms although they do not directly contribute to it. In Co2 compounds, a change of the C element changes the contribution of the t2g states to the moment at the Co sites. The localized moment in these magnetic compounds resides at the B site. Other than in the classical Cu2-based Heusler compounds, the A atoms in Co2, Fe2 and Mn2-based compounds may contribute significantly to the total magnetic moment. It is shown that the inclusion of electron–electron correlation in the form of LDA + U calculations helps to understand the magnetic properties of those compounds that already exhibit a minority gap in calculations where it is neglected. Besides the large group of Co2 compounds, half-metallic ferromagnetism was here found only in such compounds that contain Mn.
617 citations