Investigation of atomic anti-site disorder and ferrimagnetic order in the half-metallic Heusler alloy Mn2V Ga
TL;DR: The percentage of atomic anti-site disorder is deduced from the refinement of the higher angle room temperature (300 K) neutron diffraction pattern and it was observed to be roughly 8% in this sample.
Abstract: The band structure calculation for the compound Mn(2)VGa carried out using the plane wave self-consistent field package with generalized gradient approximation shows that the compound is nearly half-metallic at the equilibrium lattice parameter. However, theoretical investigations have shown that a certain percentage of atomic anti-site disorder can destroy the half-metallic nature of the sample. Hence it is important to quantify the site disorder in these systems. We have deduced the percentage of atomic anti-site disorder from the refinement of the higher angle room temperature (300 K) neutron diffraction (ND) pattern and it was observed to be roughly 8% in our sample. The field variation of resistance recorded at different temperatures shows a positive slope at low temperatures and a negative slope at higher temperatures, indicating the half-metallic character at low temperatures. The ab initio calculations predict a ferrimagnetic ground state for this system. The analysis of the magnetic structure from ND data measured at 6 K yields magnetic moment values of 1.28 μ(B) and -0.7 μ(B) for Mn and V, respectively, confirming the ferrimagnetic ordering.
Citations
More filters
01 Apr 2009
TL;DR: In this article, the performance of recent density functionals for the exchange-correlation energy of a nonmolecular solid, by applying accurate calculations with the GAUSSIAN, BAND, and VASP codes to a test set of 24 solid metals and nonmetals.
Abstract: We assess the performance of recent density functionals for the exchange-correlation energy of a nonmolecular solid, by applying accurate calculations with the GAUSSIAN, BAND, and VASP codes to a test set of 24 solid metals and nonmetals. The functionals tested are the modified Perdew-Burke-Ernzerhof generalized gradient approximation PBEsol GGA, the second-order GGA SOGGA, and the Armiento-Mattsson 2005 AM05 GGA. For completeness, we also test more standard functionals: the local density approximation, the original PBE GGA, and the Tao-Perdew-Staroverov-Scuseria meta-GGA. We find that the recent density functionals for solids reach a high accuracy for bulk properties lattice constant and bulk modulus. For the cohesive energy, PBE is better than PBEsol overall, as expected, but PBEsol is actually better for the alkali metals and alkali halides. For fair comparison of calculated and experimental results, we consider the zeropoint phonon and finite-temperature effects ignored by many workers. We show how GAUSSIAN basis sets and inaccurate experimental reference data may affect the rating of the quality of the functionals. The results show that PBEsol and AM05 perform somewhat differently from each other for alkali metal, alkaline-earth metal, and alkali halide crystals where the maximum value of the reduced density gradient is about 2, but perform very similarly for most of the other solids where it is often about 1. Our explanation for this is consistent with the importance of exchange-correlation nonlocality in regions of core-valence overlap.
413 citations
TL;DR: In this article, a quaternary Heusler half-metallic ferromagnets CoFeCrZ was designed and its first-principles calculations showed that, within a generalized gradient approximation for the electronic exchange correlation functional, both CoFeFeCrGa and CoFeGe are nearly halfmetals.
229 citations
TL;DR: In this article, the first-principles calculations were performed to find new spin-polarized materials in binary, ternary and quaternary Heusler alloys.
28 citations
TL;DR: In this paper, a systematic study of the experimental parameters to control size and morphology of half-metals Heusler nanoparticles synthesized by pulsed laser deposition (PLD) technique is presented.
20 citations
TL;DR: In this article, structural, magnetic, and magnetocaloric properties of the Heusler alloys for spintronic and magnetic refrigerator applications were reported, and they were shown to possess a cubic structure.
Abstract: We report the structural, magnetic, and magnetocaloric properties of ${\mathrm{Co}}_{2}{\mathrm{Cr}}_{1\ensuremath{-}x}{\mathrm{Ti}}_{x}\mathrm{Al}$ ($x=$ 0--0.5) Heusler alloys for spintronic and magnetic refrigerator applications. Room-temperature x-ray diffraction and neutron diffraction patterns along with Rietveld refinements confirm that the samples are of single phase and possess a cubic structure. Interestingly, magnetic susceptibility measurements indicate a second-order phase transition from paramagnetic to ferromagnetic where the Curie temperature (${T}_{C}$) of ${\mathrm{Co}}_{2}\mathrm{CrAl}$ increases from 330 K to 445 K with Ti substitution. Neutron powder diffraction data of the $x=$ 0 sample across the magnetic phase transition taken in a large temperature range confirm the structural stability and exclude the possibility of antiferromagnetic ordering. The saturation magnetization of the $x=$ 0 sample is found to be 8000 emu/mol (1.45 ${\ensuremath{\mu}}_{\mathrm{B}}$/f.u.) at 5 K, which is in good agreement with the value $(1.35\ifmmode\pm\else\textpm\fi{}0.05\phantom{\rule{4pt}{0ex}}{\ensuremath{\mu}}_{\mathrm{B}}$/f.u.) obtained from the Rietveld analysis of the neutron powder diffraction pattern measured at a temperature of 4 K. By analyzing the temperature dependence of the neutron data of the $x=$ 0 sample, we find that the change in the intensity of the most intense Bragg peak (220) is consistent with the magnetization behavior with temperature. Furthermore, an enhancement of change in the magnetic entropy and relative cooling power values has been observed for the $x=$ 0.25 sample. Interestingly, the critical behavior analysis across the second-order magnetic phase transition and extracted exponents ($\ensuremath{\beta}\ensuremath{\approx}$ 0.496, $\ensuremath{\gamma}\ensuremath{\approx}$ 1.348, and $\ensuremath{\delta}\ensuremath{\approx}$ 3.71 for the $x=$ 0.25 sample) suggest the presence of long-range ordering, which deviates toward 3D Heisenberg-type interactions above ${T}_{C}$, consistent with the interaction range value $\ensuremath{\sigma}$.
18 citations
References
More filters
TL;DR: This review describes a new paradigm of electronics based on the spin degree of freedom of the electron, which has the potential advantages of nonvolatility, increased data processing speed, decreased electric power consumption, and increased integration densities compared with conventional semiconductor devices.
Abstract: This review describes a new paradigm of electronics based on the spin degree of freedom of the electron. Either adding the spin degree of freedom to conventional charge-based electronic devices or using the spin alone has the potential advantages of nonvolatility, increased data processing speed, decreased electric power consumption, and increased integration densities compared with conventional semiconductor devices. To successfully incorporate spins into existing semiconductor technology, one has to resolve technical issues such as efficient injection, transport, control and manipulation, and detection of spin polarization as well as spin-polarized currents. Recent advances in new materials engineering hold the promise of realizing spintronic devices in the near future. We review the current state of the spin-based devices, efforts in new materials fabrication, issues in spin transport, and optical spin manipulation.
9,917 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: A revised Perdew-Burke-Ernzerhof generalized gradient approximation is introduced that improves equilibrium properties of densely packed solids and their surfaces.
Abstract: Popular modern generalized gradient approximations are biased toward the description of free-atom energies. Restoration of the first-principles gradient expansion for exchange over a wide range of density gradients eliminates this bias. We introduce a revised Perdew-Burke-Ernzerhof generalized gradient approximation that improves equilibrium properties of densely packed solids and their surfaces.
7,797 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