To seek half-metallic ferromagnets compatible with the GeSi semiconductor, we use state-of-the-art density-functional-theory methods to study cubic $\mathrm{VGe_3Si_4}$. After optimizing its crystal structure with various magnetic orders considered, we find the ferromagnetic structure is the ground state phase and investigate its stability, and then study its spin-resolved electronic structure with an improved method. Our calculated results show that the cubic $\mathrm{VGe_3Si_4}$ is a half-metallic ferromagnet with half-metallic gap 350 meV, and it is structurally stable against deformations and magnetically robust against antiferromagnetic fluctuations. These results make us believe that the cubic $\mathrm{VGe_3Si_4}$ could be synthesized as good thin films soon and used in practical spintronic devices.
We find that three nonstoichiometric cubic binary chromium chalcogenides, namely Cr3S4, Cr3Se4, and Cr3Te4, are stable half-metallic ferromagnets with wide half-metallic gaps on the basis of systematic state-of-the-arts first-principles calculations. We optimize their structures, and then calculate their magnetic moments, electronic structures, formation heats, and elastic moduli and investigate their structural stability and robustness of ferromagnetism against antiferromagnetic fluctuations. Our calculated results show that the three sulvanite phases are structurally stable and ferromagnetic…
Periodic structures of GdN particles encapsulated in a single crystalline GaN matrix were prepared by plasma assisted molecular beam epitaxy. High resolution X-ray diffractometery shows that GdN islands, with rock salt structure are epitaxially oriented to the wurtzite GaN matrix. Scanning transmission electron microscopy combined with in-situ reflection high energy electron diffraction allows for the study of island formation dynamics, which occurs after 1.2 monolayers of GdN coverage. Magnetometry reveals two ferromagnetic phases, one due to GdN particles with Curie temperature of 70K and a …
The electronic and magnetic properties of transition-metal doped $β$-Ge3N4 have been studied using first-principles calculations. The results show that the substitutional transition-metal impurities tend to cluster. The V and Cr doped Ge3N4 compounds are ferromagnetic semiconductors, while the compounds with Mn and Fe doping show a half-metallic ferromagnetic character.
General expressions for the longitudinal and transverse resistivities of single-crystalline cubic and tetragonal ferromagnets are derived from a series expansion of the resistivity tensor with respect to the magnetization orientation. They are applied to strained (Ga,Mn)As films, grown on (001)- and (113)A-oriented GaAs substrates, where the resistivities are theoretically and experimentally studied for magnetic fields rotated within various planes parallel and perpendicular to the sample surface. We are able to model the measured angular dependences of the resistivities within the framework o…
Two-dimensional (2D) ferromagnetic materials present promising candidates for spintronic devices, and the half-metallic materials with 100% spin polarization at Fermi energy level are highly desired for many spin-based devices. 2D Janus materials have attracted great attention in recent years due to their excellent properties induced by breaking the symmetry. Here, using the density functional theory, we report that the Janus V2AsP monolayer demonstrates a charming ferromagnetic half-metallic feature. It is dynamically stable in view of the absence of imaginary frequency phonon. The half-metal…
An accurate density-functional method is used to study systematically half-metallic ferromagnetism and stability of zincblende phases of 3d-transition-metal chalcogenides. The zincblende CrTe, CrSe, and VTe phases are found to be excellent half-metallic ferromagnets with large half-metallic gaps (up to 0.88 eV). They are mechanically stable and approximately 0.31-0.53 eV per formula unit higher in total energy than the corresponding nickel-arsenide ground-state phases, and therefore would be grown epitaxially in the form of films and layers thick enough for spintronic applications.
Half-metallic ferromagnetism (HMFM) occurs rarely in materials and yet offers great potential for spintronic devices. Recent experiments suggest a class of compounds with the `ThCr$_{2}$Si$_{2}$' (122) structure -- isostructural and containing elements common with Fe pnictide-based superconductors -- can exhibit HMFM. Here we use $ab$ $initio$ density-functional theory calculations to understand the onset of half-metallicity in this family of materials and explain the appearance of ferromagnetism at a quantum critical point. We also predict new candidate materials with HMFM and high Curie temp…
Parametric plots of the remagnetization versus demagnetization remnances were found for four metallic ferromagnets -- nickel wire, two types of AlNiCo, and samarium cobalt 2:17. These plots, known as Henkel plots, were compared to Wohlfarth's model for noninteracting magnetic particles and several Preisach models. The remagnetization data were taken with a variety of paths to the net zero magnetization state. The resulting Henkel plots exhibit similarities to independent Monte Carlo simulations. The differences can be mostly explained by considering that the magnetization in the metallic ferro…
Using theoretical arguments, we show that, in order to exploit half-metallic ferromagnets in tunneling magnetoresistance (TMR) junctions, it is crucial to eliminate interface states at the Fermi level within the half-metallic gap; contrary to this, no such problem arises in giant magnetoresistance elements. Moreover, based on an a priori understanding of the electronic structure, we propose an antiferromagnetically coupled TMR element, in which interface states are eliminated, as a paradigm of materials design from first principles. Our conclusions are supported by ab-initio calculations.
The temperature dependence of the magnetization and spin-polarization at the Fermi level is investigated for half-metallic ferromagnets. We reveal a new mechanism, where the hybridization of states forming the half-metallic gap depends on thermal spin fluctuations and the polarization can drop abruptly at temperatures much lower than the Curie point. We verify this for NiMnSb by ab-initio calculations. The thermal properties are studied by mapping ab-initio results to an extended Heisenberg model which includes longitudinal fluctuations and is solved by a Monte Carlo method.
We study spin-scattering asymmetry at the interface of two ferromagnets (FMs) based on a half-metallic Co$_{2}$Fe$_{0.4}$Mn$_{0.6}$Si (CFMS)/CoFe interface. First-principles ballistic transport calculations based on Landauer formula for (001)-CoFe/CFMS/CoFe indicate strong spin-dependent conductance at the CFMS/CoFe interface, suggesting a large interface spin-scattering asymmetry coefficient ($γ$). Fully epitaxial current-perpendicular-to-plane giant magnetoresistance (CPP-GMR) pseudo-spin-valve (PSV) devices involving CoFe/CFMS/Ag/CFMS/CoFe structures exhibit an enhancement in MR output owin…
The first-principles full-potential linearized augmented plane-wave method based on density functional theory is used to investigate electronic structure and magnetic properties of hypothetical binary compounds of I$^{A}$ subgroup elements with nitrogen (LiN, NaN, KN and RbN) in assumed three types of cristalline structure (rock salt, wurtzite and zinc-blende). We find that, due to the spin polarized \textit{p} orbitas of N, all four compounds are half-metallic ferromagnets with wide energy bandgaps (up to 2.0 eV). The calculated total magnetic moment in all investigated compounds for all thre…
Using first-principles calculations within generalized gradient approximation, the electronic and magnetic properties of zinc blende (zb) CrP/MnP superlattice are investigated. The equilibrium lattice constant is calculated to be $5.33\,$Å. The stability of ferromagnetic zb CrP/MnP superlattice against antiferromagnetism is considered and it is found that the ferromagnetic CrP/MnP superlattice is more stable than the antiferromagnetic one. It is shown that at the equilibrium lattice constant the CrP/MnP superlattice does not show any half metallicity mainly due to the minority $t_{2g}$ states …
Half-Heusler compounds with 18 valence electrons are semi-conducting. It will be shown that doping with electrons results in half-metallic ferromagnets, similar to the case of diluted semi-conductors. CoTiSb is known to be a semi-conducting Half-Heusler compound. Doping by Fe is expected to result in ferromagnetic order. It was found that Ti can be replaced by up to about 10% Fe while its crystal structure still remains C1b, which was proved by X-ray powder diffraction. SQUID magnetometry revealed a magnetic moment of 0.32 mB per unit cell at 5K.
We investigated the electronic and magnetic properties of a series of zinc-blend II-V compounds by carrying out density-functional-theory calculations including spin-orbit couplings. Contrary to the case of CaN and CaP, the half-metallic characteristics of the II-V compounds such as CaSb and CaBi were found to be destroyed. Our analysis of the valence band structures of CaAs, CaSb, and CaBi revealed a critical role of the spin-orbit coupling interactions on the exchange-split band structure, thereby leading to breakdown of the half-metallic ferromagnetism for the systems with heavier group V e…
We theoretically investigate spin transport in half-metallic ferromagnets at finite temperatures. The side-jump and skew-scattering contributions to spin Hall conductivity are derived using the Kubo formula. The electron-magnon interaction causes a finite density of states in the energy gap of the minority-spin band and induces spin Hall conductivity. We show that spin Hall conductivity is proportional to $T^{3/2}$, with $T$ being temperature and is sensitive to $T$. We propose that spin Hall conductivity may be a tool to study the minority-spin state.
We use first-principles theory to predict that the application of uniaxial compressive strain leads to a transition from an antiferromagnetic insulator to a ferromagnetic half-metal phase in LaMnO$_3$. We identify the Q2 Jahn-Teller mode as the primary mechanism that drives the transition, indicating that this mode can be used to tune the lattice, charge, and spin coupling. Applying $\simeq$ 6 GPa of uniaxial pressure along the [010] direction activates the transition to a half-metallic $\textit{pseudo-cubic}$ state. The half-metallicity opens the possibility of producing colossal magnetoresis…
We investigate the electronic structures and magnetic properties of RbSe and CsTe compounds in CsCl, RS and ZB structures by using first-principles calculation. It is shown that these two compounds exhibit half-metallic ferromagnetism with an integer magnetic moment of 1.00 $μ_B$ per formula in all the three structures. Total energy calculations indicate the CsCl phase is more stable than the other two phases. We investigate these two compounds with CsCl structure in detail. The ferromagnetism results mainly from the spin-polarization of p states of anion Se (Te) for the two compounds. The hal…
Based on the first-principles evolutionary materials design, we report a stable boron Kagome lattice composed of triangles in triangles on a two-dimensional sheet. The Kagome lattice can be synthesized on a silver substrate, with selecting Mg atoms as guest atoms. While the isolated Kagome lattice is slightly twisted without strain, it turns into an ideal triangular Kagome lattice under tensile strain. In the triangular Kagome lattice, we find the exotic electronic properties, such as topologically non-trivial flat band near the Fermi energy and half-metallic ferromagnetism, and predict the qu…
We have studied zig-zag boron nitride (BN) nanotubes doped with the Ni hexagonal-closepacked nanowire. The doped BN nanotubes are ferromagnetic metals with substantial magnetism. Some special magnetic properties resulting from the interaction between the Ni nanowire and BN nanotubes are found. The Ni doped BN(9,0) nanotube shows semi-half-metallic behavior, which could become half-metallic after doping electrons more than 1.4 e/unit cell. The intrinsic halfmetallic behavior could be achieved by two dierent ways: one is coating the Ni nanowire with a smaller BN nanotube, i.e., BN(8,0), the othe…
Based on the different covalent versus ionic chemical bonding and isoelectronic rutile CrO2, CrNF is proposed starting from ordered rutile derivative structures subjected to full geometry optimizations. The ground state structure defined from cohesive energies is of MgUO4-type, characterized by short covalent Cr-N and long ionic Cr-F distances. Like CrO2 it is a half-metallic ferromagnet with M = 2 Bohr Magnetons integer magnetization per formula unit with reduced band gap at minority spins. Major differences of magnetic response to pressure characterize CrNF as a soft ferromagnet versus hard …
MXenes are rapidly emerging two-dimensional (2D) materials with thickness, composition, and functionalization-dependent outstanding properties having applications in diverse fields. To disclose nano-spintronic applications of 2D-double transition metal (DTM) carbide and nitride-based pristine and surface-functionalized MXenes (M'2M"X2Tx, M' and M" = Cr, Mo, W; X = C/N; T = -F/-OH/=O), a systematic investigation has been performed on structural stability, magnetic properties and electronic structure using spin-polarized first-principles calculations. 36 stables functionalized MXenes were screen…
In this report the Co2 based Heusler compounds are discussed as potential materials for spin voltage generation. The compounds were synthesized by arcmelting and consequent annealing. Band structure calculations were performed and revealed the compounds to be half-metallic ferromagnets. Magnetometry was performed on the samples and the Curie temperatures and the magnetic moments were determined. The Seebeck coefficients were measured from low to ambient temperatures for all compounds. For selected compounds high temperature measurements up to 900 K were performed.
Electronic structure calculation were used to predict a new material for spintronic applications. Co2Mn0.5Fe0.5Si is one example which is stable against on-site correlation and disorder effects due to the position of the Fermi energy in the middle of the minority band gap. Experimentally the sample were made exhibiting L21 structure and a high magnetic order.
Two-dimensional (2D) intrinsic half-metallic materials are of great interest to explore the exciting physics and applications of nanoscale spintronic devices, but no such materials have been experimentally realized. Using first-principles calculations based on density-functional theory (DFT), we predicted that single-layer MnAsS$_4$ was a 2D intrinsic ferromagnetic (FM) half-metal. The half-metallic spin gap for single-layer MnAsS$_4$ is about 1.46 eV, and it has a large spin splitting of about 0.49 eV in the conduction band. Monte Carlo simulations predicted the Curie temperature (\emph{T}$_c…
Co$_2$FeSi crystallizes in the ordered L2$_1$ structure as proved by X-ray diffraction and Mößbauer spectroscopy. The magnetic moment of Co$_2$FeSi was measured to be about $6μ_B$ at 5K. Magnetic circular dichroism spectra excited by soft X-rays (XMCD) were taken to determine the element specific magnetic moments of Co and Fe. The Curie temperature was measured with different methods to be ($1100\pm20$)K. Co$_2$FeSi was found to be the Heusler compound as well as the half-metallic ferromagnet with the highest magnetic moment and Curie temperature.
Using first principles calculations as based on density functional theory, we propose a class of so far unexplored diluted ferromagnetic semiconductors and half-metals. Here, we study the electronic properties of recently synthesized $ 4d $ and $ 5d $ transition metal dinitrides. In particular, we address Mn- and Fe-substitution in PtN$_2$ and PdN$_2$. Structural relaxation shows that the resulting ordered compounds, Pt$_{0.75}$(Mn,Fe)$_{0.25}$N$_2$ and Pd$_{0.75}$(Mn,Fe)$_{0.25}$N$_2$, maintain the cubic crystal symmetry of the parent compounds. On substitution, all compounds exhibit long-ran…
Using the accurate first-principle method within density-functional theory, we systematically study CrSb in the zincblende (zb) structure. The zb CrSb is predicted of robust half-metallic ferromagnetism (HMFM) with a magnetic moment of 3.000 $μ_B$ per formula. It is much better than other zb compounds with HMFM because its spin-flip gap reaches 0.774 eV at the equilibrium volume and persists nonzero with its volume changing theoretically from -21% to +60%. It is found there may be a common mechanism for the HMFM in all the zb Cr- and Mn-pnictides. Since being compatible with the III-V semicond…
Development of a magnetic interatomic potential for cubic anti-ferromagnets: the case of NiO
IT4Innovations VŠB - Technical University of Ostrava（IT4创新与卓越中心 俄斯特拉发理工大学）；Departamento de Física, Universidad de Oviedo（奥维耶多大学物理系）；ASturias RAw Materials Institute (ASRAM), Universidad de Oviedo（奥维耶多大学阿斯特里亚斯原材料研究所）；Department of Condensed Matter Physics Faculty of Mathematics and Physics Charles University（查理大学数学与物理学院凝聚态物理系）
In this research paper, we investigated the structural, electronic, and magnetic features of titanium atom substituting calciumatom in rock salt structure of CaS to explore the new dilute magnetic semiconductor compounds. The calculations are carried out using the full potential linearized augmented plane wave (FP-LAPW) method based on spin-polarized density functional theory, implemented in WIEN2k code. The generalized gradient approximation and Tran-Balaha modified Becke-Johnson exchange potential. The stability of Ti doped CaS in ferromagnetic state is provided by the total energy released …
We propose and investigate the properties of a digital ferromagnetic heterostructure (DFH) consisting of a $δ$-doped layer of Mn in Si, using \textit{ab initio} electronic-structure methods. We find that (i) ferromagnetic order of the Mn layer is energetically favorable relative to antiferromagnetic, and (ii) the heterostructure is a two-dimensional half metallic system. The metallic behavior is contributed by three majority-spin bands originating from hybridized Mn-$d$ and nearest-neighbor Si-$p$ states, and the corresponding carriers are responsible for the ferromagnetic order in the Mn laye…
We consider electron transport in a nearly half-metallic ferromagnet, in which the minority spin electrons close to the band edge at the Fermi energy are Anderson-localized due to disorder. For the case of spin-flip scattering of the conduction electrons due to the absorption and emission of magnons, the Boltzmann equation is exactly soluble to the linear order. From this solution we calculate the temperature dependence of the resistivity due to single magnon processes at sufficiently low temperature, namely $k_BT\ll D/L^2$, where $L$ is the Anderson localization length and $D$ is the magnon s…
Discovery of intrinsic two-dimensional (2D) magnetic materials is crucial for understanding the fundamentals of 2D magnetism and realizing next-generation magnetoelectronic and magneto-optical devices. Although significant efforts have been devoted to identifying 2D magnetism by exfoliating bulk magnetic layered materials, seldom studies are performed to synthesize ultra-thin magnetic materials directly for non-layered magnetic materials. Here, we report the successful synthesis of a new type of theoretically proposed 2D metallic ferromagnet 1T FeS2, through the molten-salt-assisted chemical v…
Using first-principles calculations, the electronic and magnetic properties of orthorhombic BaFeO$_{3}$ (BFO) are investigated with local spin density approximation (LSDA). The calculations reveal that at the optimized lattice volume BFO has a lower energy in ferromagnetic state as compared with antiferromagnetic state. At the equilibrium volume, BFO shows metallic behavior, however, under a large tensile strain ($\sim25\%$), BFO shows half-metallic behavior consistent with the integer magnetic moment of $4.0μ_{\rm{B}}$/fu mainly caused by the $t_{2g}$ and $e_{g}$ electrons of Fe. Including a …
We complete the analysis initiated in [5] on the micromagnetics of cubic ferromagnets in which the role of magnetostriction is significant. We prove ansatz-free lower bounds for the scaling of the total micromagnetic energy including magnetostriction contribution, for a two-dimensional sample. This corresponds to the micromagnetic energy-per-unit-length of an infinitely thick sample. A consequence of our analysis is an explanation of the multi-scale zig-zag Landau state patterns recently reported in single crystal Galfenol disks from an energetic viewpoint. Our proofs combines a number of well…
The electronic and magnetic properties of pristine CrPSe$_3$ and mixed Cr$_{1\textrm{-}x}$M$_x$PSe$_3$ (M = Zn, Cd, Hg) monolayers were studied using density functional theory including an on-site Coulomb term (DFT$+U$) and tight-binding approach (TBA). While pristine CrPSe$_3$ monolayer has an antiferromagnetic (AFM) ground state, its alloying with MPSe$_3$ may give rise to half-metallic ferromagnet (HMF) with high Curie temperature. The resulting monolayers demonstrate single-spin Dirac cones of mainly Cr-$d$ character located in the first Brillouin zone directly at the Fermi energy. The cal…
The emergence of the field of spintronics brought half-metallic ferromagnets to the center of scientific research. A lot of interest was focused on newly created transition-metal pnictides (such as CrAs) and chalcogenides (such as CrTe) in the metastable zinc-blende lattice structure. These compounds were found to present the advantage of high Curie temperature values in addition to their structural similarity to semiconductors. Significant theoretical activity has been devoted to the study of the electronic and magnetic properties of these compounds in an effort to achieve a better control of…
We introduce a path to a possibly new class of magnetic materials whose properties are determined entirely by the presence of a low concentration of specific point defects in their crystal structure. Using model Hamiltonian and ab-initio band structure methods we demonstrate that even large band gap nonmagnetic materials as simple as CaO can exhibit extraordinary properties like half metallic ferromagnetism upon introducing a small concentration of Ca vacancies. We show that such defects will initially bind the introduced charge carriers at neighboring sites and depending on the internal symme…
Six half-metallic ferromagnets X0.75Y0.25C (X=Si, Ge, Sn and Y =Ca and Sr) with zinc-blende structure, resulting from alkaline-earth (Ca, Sr) substitution for X, are predicted based on the density functional theory. The calculated total magnetic moments of these ferromagnets are all integer 2.00μB per supercell, which are one of important characters of half-metallic ferromagnets. Our calculations indicate that X0.75Y0.25C have wide spin gap and potentially have high Curie temperature. Alkaline-earth doping results in the spin-polarization and half-metallicity of these compounds. It is confirme…
Using the recently developed Nth-order muffin-tin-orbital (NMTO) based downfolding technique we revisit the electronic properties of half-metallic ferromagnets, the semi-Heusler NiMnSb and rutile CrO2. The NMTO Wannier orbitals for the Mn-d and Cr-t2g manifolds are constructed and the mechanism of chemical bonding is discussed. The effective hopping Hamiltonian parameters are calculated using a NMTO downfolded basis set. We propose model Hamiltonian parameters with possibly minimal basis sets for both half-metallic ferromagnetic alloys.
The electronic structure of the VAs compound in the zinc-blende structure is investigated using a combined density-functional and dynamical mean-field theory approach. Contrary to predictions of a ferromagnetic semiconducting ground state obtained by density-functional calculations, dynamical correlations induce a closing of the gap and produce a half-metallic ferromagnetic state. These results emphasize the importance of dynamic correlations in materials suitable for spintronics.
Temperature variation of resistivity and specific heat have been measured for prototypical half-metallic ferromagnets, R_0.6Sr_0.4MnO_3, with controlling the one-electron bandwidth W. We have found variation of the temperature scalings in the resistivity from T^2 (R = La, and Nd) to T^3 (R = Sm), and have interpreted the $T^3-law in terms of the anomalous single-magnon scattering (AMS) process in the half-metallic system.
A brief review of experimental and theoretical studies of half-metallic ferromagnets (HMF) and spin gapless semiconductors (SGS) is given. The data on resistivity and magnetoresistivity are presented. An important role of non-quasiparticle states owing to electron-magnon scattering in transport properties is discussed. The problem of low-temperature resistivity in HMF is treated in terms of one-magnon and two-magnon scattering processes.
The magnetoresistance (MR) in polycrystalline colossal magnetoresistive compounds follows a behavior different from single crystals below the ferromagnetic transition temperature. This difference is usually attributed to spin polarized tunneling at the grain boundaries of the polycrystalline sample. Here we derive a theoretical expression for the contribution of spin polarized tunneling to the magnetoresistance in granular ferromagnetic systems under the mean field approximation. We apply this model to our experimental data on the half metallic ferromagnet La0.7Sr0.3MnO3, and find that the the…
We investigate the growth of half metallic phase in a ferromagnetic material using state-of-the-art full potential linearized augmented plane wave method. To address the issue, we have substituted Ti at the Ru-sites in SrRuO3, where SrRuO3 is a ferromagnetic material. Calculated results establish Ti4+ valence states (similar to SrTiO3), which was predicted experimentally. Thus, Ti substitution dilutes the Ru-O-Ru connectivity, which is manifested in the calculated results in the form of significant band narrowing leading to finite gap between t2g and eg bands. At 75% substitution, a large gap …
We present electronic structure calculations in combination with local and non-local many-body correlation effects for the half-metallic ferromagnet CrO$_2$. Finite-temperature Dynamical Mean Field Theory results show the existence of non-quasiparticle states, which were recently observed as almost currentless minority spin states near the Fermi energy in resonant scattering experients. At zero temperatures, Variational Cluster Approach calculations support the half-metallic nature of CrO$_2$ as seen in superconducting point contact spectroscopy. The combination of these two techniques allowed…
We point out that, contrary to an assertion by Chen, Bergman and Burkov [Phys. Rev. B 88, 125110 (2013)], the non-quantized part of the intrinsic anomalous Hall conductivity can indeed be expressed as a Fermi-surface property even when Weyl points are present in the bandstructure.
Using density functional theory we have performed theoretical investigations of the electronic properties of a free-standing one-dimensional organometallic vanadium-benzene wire. This system represents the limiting case of multi-decker V_n(C6H6)_{n+1} clusters which can be synthesized. We predict that the ground state of the wire is a 100% spin-polarized ferromagnet (half-metal). Its density of states is metallic at the Fermi energy for the minority electrons and shows a semiconductor gap for the majority electrons. We found that the half-metallic behavior is conserved up to 12%, longitudinal …
A brief survey of experimental and theoretical studies of half-metallic ferromagnets (HMFs) and spin gapless semiconductors is given, the possible candidates being the X$_2$YZ (X = Mn, Fe, Co; Y = Ti, V, Cr, Mn, Fe, Co, Ni; Z = Al, Si, Ga, Ge, In, Sn, Sb) Heusler alloys. The data on the electrical resistivity, normal and anomalous Hall Effect, and magnetic properties are presented. It is shown that the Co$_2$FeZ alloys demonstrate properties of conventional ferromagnets, the HMF properties being also manifested at the variation of the Z-component. The Fe$_2$YAl and Mn$_2$YAl alloys show at the…
A theoretical formulation of magnetoresistance effect in a metallic ferromagnetic/nonmagnetic bilayer originated from the charge-spin conversion by the anomalous Hall effect is presented. Analytical expressions of the longitudinal and transverse resistivities in both nonmagnet and ferromagnet are obtained by solving the spin diffusion equation. The magnetoresistance generated from charge-spin conversion purely caused by the anomalous Hall effect in the ferromagnet is found to be proportional to the square of the spin polarizations in the ferromagnet and has fixed sign. We also find additional …
Based on the first-principles electronic structure calculations, we predict that a chromium oxide K$_2$Cr$_8$O$_{16}$ of hollandite type should be a half-metallic ferromagnet where the Fermi level crosses only the majority-spin band, whereas the minority-spin band has a semiconducting gap. We show that the double-exchange mechanism is responsible for the observed saturated ferromagnetism. We discuss possible scenarios of the metal-insulator transition observed at low temperature and we argue that the formation of the incommensurate, long-wavelength density wave of spinless fermions caused by t…
The magneto-optical spectra of NiMnSb were calculated in the framework of the Local Spin Density Approximation (LSDA) combined with Dynamical Mean-Field Theory (DMFT). Comparing with results based on plain LSDA, an additional account of many-body correlations via DMFT results in a noticably improved agreement of the theoretical Kerr-rotation and ellipticity spectra with corresponding experimental data.
We present a theory of the infrared conductivity and absorption coefficients of metallic (III,Mn)V ferromagnetic semiconductors. We find that the conductivity is dominated by inter-valence-band transitions that produce peaks at $\hbar ω\sim 220 {\rm meV}$ and obscure the broadened Drude peak. We demonstrate that transverse f-sum rule measurements can be used to extract accurate values for the free carrier density, bypassing the severe characterization difficulties that have till now been created by the large anomalous Hall effect in these materials.
We apply the quasiparicle self-consistent $GW$ (\qsgw) method to a cubic virtual-crystal alloy La$_{1-x}$Ba$_x$MnO$_3$ %(LBMO) as a theoretical representative for colossal magnetoresistive perovskite manganites. The \qsgw\ predicts it as a fully-polarized half-metallic ferromagnet for a wide range of $x$ and lattice constant. Calculated density of states and dielectric functions are consistent with experiments. In contrast, the energies of calculated spin wave are very low in comparison with experiments. This is affected neither by rhombohedral deformation nor the intrinsic deficiency in the \…
We have investigated electronic and magnetic properties of the pyrite-type CoS_2 using the linearized muffin-tin orbital (LMTO) band method. We have obtained the ferromagnetic ground state with nearly half-metallic nature. The half-metallic stability is studied by using the fixed spin moment method. The non-negligible orbital magnetic moment of Co 3d electrons is obtained as $μ_L = 0.06 μ_B$ in the local spin density approximation (LSDA). The calculated ratio of the orbital to spin angular momenta <L_z >/< S_z > = 0.15 is consistent with experiment. The effect of the Coulomb correlation betwee…
Chromium dioxide (CrO2) offers a rare example of metallic ferromagnetism among stoichiometric transition-metal oxides. What makes it even more remarkable is the half-metallic electronic structure. Today, CrO2 is widely used in magnetorecording and regarded as a promising spintronic material. Nevertheless, the key question "Why is it ferromagnetic?" remains largely unanswered, despite general interest to the problem and practical importance of CrO2. In the present work we challenge this question by combining first-principles electronic structure calculations with the model Hamiltonian approach …
Using ab initio calculations, we have investigated a cubic perovskite BaOsO3 and a few related compounds that have been synthesized recently and formally have a metallic d^4 configuration. In BaOsO3, which shows obvious 3-dimensional fermiology, a nonmagnetism is induced by a large spin-orbit coupling (SOC), which is precisely equal to an exchange splitting ~0.4 eV of the $t_{2g}$ manifold. However, the inclusion of on-site Coulomb repulsion as small as $U^c$~1.2 eV, only 1/3 of the $t_{2g}$ bandwidth, leads to the emergence of a spin-ordered moment, indicating that this system is on the verge…
