First-Principles Calculation and Experimental Investigations on Full-Heusler Alloy Co $_{2}$ FeGe
22 Sep 2009-IEEE Transactions on Magnetics (Institute of Electrical and Electronics Engineers)-Vol. 45, Iss: 10, pp 3997-3999
TL;DR: In this paper, first principles for the full Heusler alloy Co2FeGe within the scheme of density functional theory using plane-wave self-consistent field method were carried out.
Abstract: First-principles calculation has been carried out for the full Heusler alloy Co2FeGe within the scheme of density functional theory using plane-wave self-consistent field method. The spin polarized band structure does not show any energy gap at the Fermi level for both up and down spin electrons. Atom resolved magnetic moment on each site was observed to be 1.3 muB (Co), 2.9 muB (Fe), and 0.0 muB (Ge). X-ray diffraction studies reveal a B2-type structure for the bulk sample and cubic L21 structure for the melt-spun ribbons. The lattice parameter value for the ribbon is 5.736 Aring, and its Curie temperature is around 981 K. The magnetic moment per formula unit at 5 K was observed to be 5.74 muB. The low temperature data ( < 100 K) follows the relationrho = rho0 + AT2 + BT4.5 , indicating the presence of one magnon spin-flip scattering.
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TL;DR: In this article, the half metallic ferromagnetism, structural, elastic, thermal, electronic and magnetic properties of Co2YGe (Y Mn, Fe) Heusler compounds with Fm-3m crystal structure involving the density functional theory within the framework of full potential linearized augmented plane wave method.
Abstract: The focal point of this article is to pay attention on the half metallic ferromagnetism, structural, elastic, thermal, electronic and magnetic properties of Co2YGe (Y Mn, Fe) Heusler compounds with Fm-3m crystal structure involving the density functional theory within the framework of full potential linearized augmented plane wave method as integrated in the Wien2k package. The structural optimizations plots confirm that both alloys are in the lower energy state in ferromagnetic order. Moreover the structural parameters are consistent with experiment. The computed elastic properties show the ductile nature of these alloys. Based on the thermal properties of these alloys, Co2MnGe is more favorable for the fabrication of elevated temperature acoustical devices as compared to Co2FeGe. For the calculation of electronic and magnetic properties of Co2YGe (Y Mn, Fe) alloys in addition to GGA functional, the GGA + U (U= Hubbard parameters) were also adopted. Both alloys are HMF in nature. It is also observed that the values of the compound's magnetic-moments fit excellent with Slater Pauling law. Furthermore we have calculated the formation energy and Curie temperature of these alloys. The negative values of the formation energy of both compounds represent their thermodynamic stability and strong bonding. Higher values of thermal parameters, half metallic nature and ferromagnetism of Co2YGe (Y Mn, Fe) predict the importance of these compounds in acoustical and spintronic devices respectively.
9 citations
TL;DR: In this article , the structural, martensitic transition, band structure, density of states, elastic, magnetic, and thermoelectric properties of L 2 1 and XA ordering of Co 2 FeGe compound were investigated.
9 citations
TL;DR: In this article, the anomalous Hall effect (AHE) in the full Heusler compound with cobalt as a primary element was studied. But the authors focused on anomalous hall conductivity in the case of a single element.
Abstract: Full Heusler compounds with cobalt as a primary element show anomalous transport properties owing to the Weyl fermions and broken time-reversal symmetry. We present here the study of anomalous Hall effect (AHE) in the ${\mathrm{Co}}_{2}\mathrm{FeGe}$ Heusler compound. The experiment reveals anomalous Hall conductivity (AHC) $\ensuremath{\sim}100$ S/cm at room temperature with an intrinsic contribution of $\ensuremath{\sim}78$ S/cm. The analysis of anomalous Hall resistivity suggests the scattering independent intrinsic mechanism dominates the overall behavior of anomalous Hall resistivity. The first principles calculation reveals that the Berry curvature originated by a gapped nodal line near ${E}_{F}$ is the main source of AHE in the ${\mathrm{Co}}_{2}\mathrm{FeGe}$ Heusler compound. The theoretically calculated AHC is in agreement with the experiment.
8 citations
TL;DR: In this paper, the interface magnetism between Co2FeGe Heusler alloy layers and MgO layers was investigated using 57Fe Mossbauer spectroscopy using atomically controlled alternate deposition.
Abstract: The interface magnetism between Co2FeGe Heusler alloy layers and MgO layers was investigated using 57Fe Mossbauer spectroscopy. Interface-sensitive samples, where the 57Fe isotope was used only for the interfacial atomic layer of the Co2FeGe layer on the MgO layer, were prepared using atomically controlled alternate deposition. The 57Fe Mossbauer spectra of the interface-sensitive samples at room temperature were found similar to those of the bulk-sensitive Co2FeGe films in which the 57Fe isotope was distributed throughout the films. On the other hand, the tunnel magnetoresistance effect of magnetic tunnel junctions with Co2FeGe layers as the ferromagnetic electrodes showed strong reduction at room temperature. These results indicate that the strong temperature dependence of the tunneling magnetoresistance of magnetic tunnel junctions using Heusler alloy electrodes cannot be attributed simply to the reduction of the magnetization at the interfaces between the Heusler alloy and insulator layers.
7 citations
Patent•
21 Dec 2011TL;DR: A CPP-GMR element that uses this Heusler alloy as an electrode displays the world's highest MR ratio, an STO element displays high output, and an NLSV element displays a high spin signal as discussed by the authors.
Abstract: Provided is a Heusler alloy which is Co2Fe(GaxGex-1) and satisfies 0.25 < X < 0.60, has a spin polarization rate as determined by PCAR of 0.65 or greater, and reaches a Curie point of 1,288 K. A CPP-GMR element that uses this Heusler alloy as an electrode displays the world's highest MR ratio, an STO element displays high output, and an NLSV element displays a high spin signal.
6 citations
References
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TL;DR: A simple analytic representation of the correlation energy for a uniform electron gas, as a function of density parameter and relative spin polarization \ensuremath{\zeta}, which confirms the practical accuracy of the VWN and PZ representations and eliminates some minor problems.
Abstract: We propose a simple analytic representation of the correlation energy ${\mathrm{\ensuremath{\varepsilon}}}_{\mathit{c}}$ for a uniform electron gas, as a function of density parameter ${\mathit{r}}_{\mathit{s}}$ and relative spin polarization \ensuremath{\zeta}. Within the random-phase approximation (RPA), this representation allows for the ${\mathit{r}}_{\mathit{s}}^{\mathrm{\ensuremath{-}}3/4}$ behavior as ${\mathit{r}}_{\mathit{s}}$\ensuremath{\rightarrow}\ensuremath{\infty}. Close agreement with numerical RPA values for ${\mathrm{\ensuremath{\varepsilon}}}_{\mathit{c}}$(${\mathit{r}}_{\mathit{s}}$,0), ${\mathrm{\ensuremath{\varepsilon}}}_{\mathit{c}}$(${\mathit{r}}_{\mathit{s}}$,1), and the spin stiffness ${\mathrm{\ensuremath{\alpha}}}_{\mathit{c}}$(${\mathit{r}}_{\mathit{s}}$)=${\mathrm{\ensuremath{\partial}}}^{2}$${\mathrm{\ensuremath{\varepsilon}}}_{\mathit{c}}$(${\mathit{r}}_{\mathit{s}}$, \ensuremath{\zeta}=0)/\ensuremath{\delta}${\mathrm{\ensuremath{\zeta}}}^{2}$, and recovery of the correct ${\mathit{r}}_{\mathit{s}}$ln${\mathit{r}}_{\mathit{s}}$ term for ${\mathit{r}}_{\mathit{s}}$\ensuremath{\rightarrow}0, indicate the appropriateness of the chosen analytic form. Beyond RPA, different parameters for the same analytic form are found by fitting to the Green's-function Monte Carlo data of Ceperley and Alder [Phys. Rev. Lett. 45, 566 (1980)], taking into account data uncertainties that have been ignored in earlier fits by Vosko, Wilk, and Nusair (VWN) [Can. J. Phys. 58, 1200 (1980)] or by Perdew and Zunger (PZ) [Phys. Rev. B 23, 5048 (1981)]. While we confirm the practical accuracy of the VWN and PZ representations, we eliminate some minor problems with these forms. We study the \ensuremath{\zeta}-dependent coefficients in the high- and low-density expansions, and the ${\mathit{r}}_{\mathit{s}}$-dependent spin susceptibility. We also present a conjecture for the exact low-density limit. The correlation potential ${\mathrm{\ensuremath{\mu}}}_{\mathit{c}}^{\mathrm{\ensuremath{\sigma}}}$(${\mathit{r}}_{\mathit{s}}$,\ensuremath{\zeta}) is evaluated for use in self-consistent density-functional calculations.
21,353 citations
TL;DR: Spintronics, or spin electronics, involves the study of active control and manipulation of spin degrees of freedom in solid-state systems as discussed by the authors, where the primary focus is on the basic physical principles underlying the generation of carrier spin polarization, spin dynamics, and spin-polarized transport.
Abstract: Spintronics, or spin electronics, involves the study of active control and manipulation of spin degrees of freedom in solid-state systems. This article reviews the current status of this subject, including both recent advances and well-established results. The primary focus is on the basic physical principles underlying the generation of carrier spin polarization, spin dynamics, and spin-polarized transport in semiconductors and metals. Spin transport differs from charge transport in that spin is a nonconserved quantity in solids due to spin-orbit and hyperfine coupling. The authors discuss in detail spin decoherence mechanisms in metals and semiconductors. Various theories of spin injection and spin-polarized transport are applied to hybrid structures relevant to spin-based devices and fundamental studies of materials properties. Experimental work is reviewed with the emphasis on projected applications, in which external electric and magnetic fields and illumination by light will be used to control spin and charge dynamics to create new functionalities not feasible or ineffective with conventional electronics.
9,158 citations
TL;DR: The band structure of Mn-based Heusler alloys of the crystal structure (MgAgAs type) has been calculated with the augmented-spherical-wave method.
Abstract: The band structure of Mn-based Heusler alloys of the $C{1}_{b}$ crystal structure (MgAgAs type) has been calculated with the augmented-spherical-wave method. Some of these magnetic compounds show unusual electronic properties. The majority-spin electrons are metallic, whereas the minority-spin electrons are semiconducting.
3,851 citations
TL;DR: In this article, the full-potential screened Korringa-Kohn-Rostoker method was used to study the half-metallic properties of Co, Fe, Rh, and Ru.
Abstract: Using the full-potential screened Korringa-Kohn-Rostoker method we study the full-Heusler alloys based on Co, Fe, Rh, and Ru. We show that many of these compounds show a half-metallic behavior; however, in contrast to the half-Heusler alloys the energy gap in the minority band is extremely small due to states localized only at the Co (Fe, Rh, or Ru) sites which are not present in the half-Heusler compounds. The full-Heusler alloys show a Slater-Pauling behavior and the total spin magnetic moment per unit cell ${(M}_{t})$ scales with the total number of valence electrons ${(Z}_{t})$ following the rule ${M}_{t}{=Z}_{t}\ensuremath{-}24.$ We explain why the spin-down band contains exactly 12 electrons using arguments based on group theory and show that this rule holds also for compounds with less than 24 valence electrons. Finally we discuss the deviations from this rule and the differences compared to the half-Heusler alloys.
1,688 citations
TL;DR: A review of new developments in theoretical and experimental electronic-structure investigations of half-metallic ferromagnets (HMFs) is presented in this article, where the effects of electron-magnon interaction in HMFs and their manifestations in magnetic, spectral, thermodynamic, and transport properties are considered.
Abstract: A review of new developments in theoretical and experimental electronic-structure investigations of half-metallic ferromagnets (HMFs) is presented. Being semiconductors for one spin projection and metals for another, these substances are promising magnetic materials for applications in spintronics (i.e., spin-dependent electronics). Classification of HMFs by the peculiarities of their electronic structure and chemical bonding is discussed. The effects of electron-magnon interaction in HMFs and their manifestations in magnetic, spectral, thermodynamic, and transport properties are considered. Special attention is paid to the appearance of nonquasiparticle states in the energy gap, which provide an instructive example of essentially many-body features in the electronic structure. State-of-the-art electronic calculations for correlated d-systems are discussed, and results for specific HMFs (Heusler alloys, zinc-blende structure compounds, CrO2, and Fe3O4) are reviewed.
748 citations