Full-potential Local Orbitals Research Articles

Magnetic properties and structural phase transition in ultrathin fcc Fe(111) and bcc Fe(111) films: First-principles study

The aim of this work is to investigate the structural and magnetic characteristics of Fe thin films with a triangular (hexagonal) lattice surfaces (fcc (111) and bcc (111)). The properties of these structures have been calculated using density functional theory (DFT) implemented in the full-potential local-orbital (FPLO) code. The results indicate a structural phase transition from fcc to bcc structure when the film thickness exceeds 23 Fe atomic monolayers. The considered fcc films prefer the low-spin ferromagnetic state with an average magnetic moment of about 1.0 μB per atom. This moment decreases with increasing film thickness until the critical thickness, where, after the structural transition to the bcc phase, it reaches a value close to that of bulk bcc Fe. Moreover, the values of the magnetic anisotropy energy are positive (perpendicular magnetic anisotropy) for the entire thickness range of films with fcc structure (in ferromagnetic low-spin state) and systematically decrease with increasing film thickness. The presented computational results explain the experimentally observed structural transition and may help to select appropriate substrates with suitable lattice parameters for the deposition of ultrathin Fe(111) films.

DFT calculation of intrinsic properties of magnetically hard phase L10 FePt

Due to its strong magnetocrystalline anisotropy, FePt L1$\mathrm{_0}$ phase is considered as a promising magnetic recording media material. Although the magnetic properties of this phase have already been analyzed many times using density functional theory (DFT), we decided to study it again, emphasizing on full potential methods, including spin-polarized relativistic Korringa-Kohn-Rostoker (SPR-KKR) and full-potential local-orbital (FPLO) scheme. In addition to the determination of exact values of the magnetocrystalline anisotropy constants K$\mathrm{_1}$ and K$\mathrm{_2}$, the magnetic moments (m), the Curie temperature, and the magnetostriction coefficient, we focused on the investigation of the magnetocrystalline anisotropy energy (MAE) dependence on the magnetic moment values using the fully relativistic fixed spin moment (FSM) method with various exchange-correlation potentials. We present nearly identical MAE(m) curves near the equilibrium point, along with different equilibrium values of MAE and magnetic moments. For a magnetic moment reduced by about 10%, we determined a theoretical MAE maximum in the ground state (0 K) equal to about 20.3 MJ m$\mathrm{^{-3}}$ and independent of the choice of the exchange-correlation potential form. These calculations allow us to understand the discrepancies between the previous MAE results for different exchange-correlation potentials.

Magnetic properties of 3d, 4d, and 5d transition-metal atomic monolayers in Fe/TM/Fe sandwiches: Systematic first-principles study

Previous studies have accurately determined the effect of transition metal point defects on the properties of bcc iron. The magnetic properties of transition metal monolayers on the iron surfaces have been studied equally intensively. In this work, we investigated the magnetic properties of the 3d, 4d, and 5d transition-metal (TM) atomic monolayers in Fe/TM/Fe sandwiches using the full-potential local-orbital (FPLO) scheme of density functional theory. We prepared models of Fe/TM/Fe structures using the supercell method. We selected the total thickness of our system so that the Fe atomic layers furthest from the TM layer exhibit bulk iron-bcc properties. Along the direction perpendicular to the TM layer, we observe oscillations of spin and charge density. For Pt and W we obtained the largest values of perpendicular magnetocrystalline anisotropy and for Lu and Ir the largest values of in-plane magnetocrystalline anisotropy. All TM layers, except Co and Ni, reduce the total spin magnetic moment in the generated models, which is in good agreement with the Slater-Pauling curve. Density of states calculations showed that for Ag, Pd, Ir, and Au monolayers, a distinct van Hove singularity associated with TM/Fe interface can be observed at the Fermi level.

Enhancing of hydrogen storage properties of perovskite-type MgNiH3 by introducing cobalt dopant (MgCoxNi1−xH3) using first-principle calculations

First-principle calculations have been performed to study the intermetallic alloys MgCoxNi1−x and intermetallic hydrides MgCoxNi1−xH3 using full-potential local orbital (FPLO). The electronic structure of Mg-hydride-based alloys has been elaborated to predict further modifications which destabilize the corresponding hydrides. In this paper, we have demonstrated that the insertion of Co element plays a crucial role in the stability of doped intermetallic hydrides (MgCo0.50Ni0.50H3, MgCo0.75Ni0.25H3 and MgCo0.875Ni0.125H3), by enhancing the hydrogen storage capacities which becomes around 3.488 wt%, also the desorption temperature has improved significantly. Therefore, the mixture between Co and Ni plays an important role in the hydrogen uptake mechanism in the target intermetallic matrix.

Electronic structure of CeCo1−xFexGe3 studied by X-ray photoelectron spectroscopy and first-principles calculations

A transformation between the magnetically ordered CeCoGe3 and heavy fermion CeFeGe3 is isostructural but not isoelectronic, therefore the characterization of the electronic structure of the CeCo1−xFexGe3 series is of special importance. We report both the experimental investigation by the X-ray photoelectron spectroscopy (XPS) measurements and the first-principles calculations within the full-potential local-orbital (FPLO) scheme based on the density functional theory. Experimentally, we investigate mainly the valence band and the Ce 3d spectra, both giving the possibility to conclude about the level of the f states localization. Computationally, we investigate the most characteristic CeCoGe3, CeCo0.5Fe0.5Ge3, and CeFeGe3 compositions. Based on the electronic band structure results we calculate the X-ray photoelectron spectra of the valence band. We consider the effects of the spin-orbit coupling and intra-atomic Hubbard U repulsion. Furthermore, we discuss the charge distribution and occupation of valence-band orbitals. The experimentally observed evolution of the 3d band with the Fe concentration is related to the decrease of the number of electrons and reduction of the 3d photoionization cross-sections. Calculations indicate that charge is transferred mainly from the Ce to Ge sites and the bondings are formed mainly by the Ce 5d, Fe/Co 3d, and Ge 4p and Ge 4s orbitals.

Electronic structures and magnetic properties of 3d magnetic atoms adsorbed on olympicene molecule: A density functional theory study

The adsorption characteristics of transition metal (TM) adatoms on olympicene, a graphene-like molecule consisting of five rings of which four are benzene-like rings, are analyzed by means of first-principles calculations. The electronic structures and magnetic properties of 3d transition metals on olympicene were investigated in the framework of generalized-gradient approximation using relativistic density functional theory. Our calculations were based on full-potential local orbital (FPLO) method. Stable structure and total energies were obtained. Relaxed TM@Olympicene molecules, unlike the pure organic olympicene, were partially buckled. Binding energy calculations showed high stability for Ni@Olympicene whereas Mn did not bind to olympicene surface. Electronic charge transfers were consistent with Pauling electronegativities. The related HOMO-LUMO gaps decreased with respect to pure olympicene. Our calculated total and TM spin magnetic moments indicated that TM@Olympicene were strongly magnetized. Orbital polarization correction (OPC) were also used in order to get an upper estimation for orbital magnetic moment of all 3d atoms. Fe@Olympicene shows highest orbital moment of 0.18 μB. The Atoms in Molecules (AIM) approach was used to analyze the nature of TMC bonds in TM@Olympicene complexes. The results show the TMC bonds have a degree of covalency in their interactions.

First principle study of magnetic and electronic properties of single X (X = Al, Si) atom added to small carbon clusters (C n X, n = 2–10)

In this paper, the magnetic and electronic properties of single aluminum and silicon atom added to small carbon clusters (C n X; X = Al, Si; n = 2–10) are studied in the framework of generalized-gradient approximation using density functional theory. The calculations were performed for linear, two dimensional and three dimensional clusters based on full-potential local-orbital (FPLO) method. The total energies, HOMO–LUMO energy gap and total magnetic moments of the most stable structures are presented in this work. The calculations show that C n Si clusters have more stability compared to C n Al clusters. In addition, our magnetic calculations were shown that the C n Al isomers are magnetic objects whereas C n Si clusters are nonmagnetic objects.

Investigating half-metallicity in PtXSb alloys (X=V, Mn, Cr, Co) at ambient and high pressure

The structural, electronic, magnetic and elastic properties of half-Heusler alloys PtMnSb, PtVSb, PtCrSb and PtCoSb are investigated using first-principles calculation based on Density Functional Theory DFT. The Full Potential local Orbital (FPLO) method, within the General Gradient Approximation (GGA) and Local Spin Density Approximation (LSDA), have been used. The calculated structural, electronic and magnetic properties are in good agreement with available experimental and theoretical data. Using GGA approximation, only PtVSb shows a half-metallic behavior with a spin-down band gap and total magnetic moment of 0.802eV and 2µB respectively. Both of PtVSb and PtMnSb alloys are half-metallic with spin-down band gaps of 0.925eV and 0.832eV and magnetic moments of 2µB and 4µB respectively using LSDA approximation. The bulk modulus and its first pressure-derivative of these alloys are calculated using the modified Birch–Murnaghan equation of state (EOS). The effect of pressure on the lattice constant, energy gap and bulk modulus is investigated. Under pressure, PtMnSb and PtCrSb turn into half-metallic alloys at nearly 6GPa and 27GPa respectively using GGA approximation.

Relativistic first-principles study on spin and orbital magnetism of mattagamite (CoTe2)

We have demonstrated electronic and magnetic properties of CoTe2 compound in the framework of relativistic density functional theory using generalized gradient approximation (GGA). The spin and orbital magnetic moments of Co and Te atoms were obtained using full-potential local orbitals band structure scheme. We have found a partially quenched orbital moment of 0.096μB for Co atom in the local spin density approximation. In order to improve the intrinsic deficiency of local density approximation for describing orbital magnetism, an orbital polarization correction was applied to CoTe2 and a significant orbital moment of 0.153μB was found for Co atom in this compound.

Electronic structure and transport properties of CeNi9In2

We investigated CeNi9In2 compound, which has been considered as a mixed valence (MV) system. Electrical resistivity vs. temperature variation was analyzed in terms of the model proposed by Freimuth for systems with unstable 4f shell. At low temperature the resistivity dependence is consistent with a Fermi liquid state with a contribution characteristic of electron–phonon interaction. Ultraviolet photoemission spectroscopy (UPS) studies of the valence band did not reveal a Kondo peak down to 14K. A difference of the spectra obtained with photon energies of low and high photoionization cross sections for Ce 4f electrons indicated that 4f states are located mainly close to the Fermi energy. The peaks related to f5/21 and f7/21 final states cannot be resolved but form a plateau between −0.3eV and the Fermi energy. X-ray photoemission spectroscopy (XPS) studies were realized for the cerium 3d level. The analysis of XPS spectra within the Gunnarsson-Schönhammer theory yielded a hybridization parameter of 104meV and non-integer f level occupation, being close to 3. Calculations of partial densities of states were realized by a full potential local orbital (FPLO) method. They confirm that the valence band is dominated by Ni 3d states and are in general agreement with the experiment except for the behavior of f-electrons.

Electronic structure of cage-type ternaries ARu2Al10 – Theory and XPS experiment (A = Ce and U)

The electronic structure of the isomorphic, orthorhombic URu2Al10 and CeRu2Al10 aluminides have been studied by X-ray photoelectron spectroscopy (XPS) and ab initio calculations using the fully relativistic full-potential local-orbital (FPLO) method within the local density approximation (LDA). The calculated data of the former system revealed fairly sharp triple-peaks of the U 5f states around the Fermi level (EF) and a large broad contribution from the Ru 4d states expanded from EF to about 6.5eV of binding energy. Although the size and positions of the Ru 4d bands for the latter compound are quite similar to those of the U-based one, the double Ce 4f sharp peaks are placed almost completely above EF underlying their mostly localized character. We have also analyzed the Fermi surfaces (FSs) in these two aluminides. The calculated results of both ternaries were then compared with our experimental XPS data for URu2Al10 and with such data for CeRu2Al10 available in the literature. The results are in fairly good agreement between the theory and experiment. Especially, the fact that the spectrum weight of the Ce 4f electrons below EF turned out to be very much reduced, reflecting rather a small f–c hybridization of these electrons compared to considerably larger one in the U-based compound.

Origin of Magnetism from Native Point Defects in ZnO

Based on the first-principle calculations by using the Korringa–Kohn–Rostoker coherent potential approximation (KKR-CPA) method in connection with the local density approximation (LDA), we study theoretically the electronic and magnetic properties of different point defects in ZnO, which are Zinc interstitials (Zni), Zinc antisites (ZnO), Oxygen interstitials (Oi) and Oxygen antisites (OZn) defects in ZnO. The supercell calculations were also performed using the full potential local-orbital (FPLO) band structure scheme. This work presents detailed information about total and local density of states at some concentrations of these defects; the stability of the ferromagnetic state compared with the spin-glass state is investigated by comparing calculating their total energy. The results show on one hand that Zni and ZnO produce a shallow donor bellow the bottom of the conduction band (CB), while Oi and OZn produces the shallow acceptors above the top of the valence band (VB), and moment magnetic; on other hand that the ferromagnetic state is more stable than the spin-glass in Oxygen interstitials (Oi) and vice versa for oxygen antisites (OZn) of native point defects in ZnO. The other native point defects (Zni, ZnO, VO, and VZn) have a zero magnetic moment. The results show that the Curie temperature increases with the concentration of interstitial oxygen.

Spin and orbital magnetism in 3d transition metal nanowires (Mn, Fe, and Co): a density functional theory study

In this work we study the electronic structure and magnetic properties of 3d transition metal nanowires (Mn, Fe, and Co). We have performed density functional calculations using the relativistic version of the full potential local orbital (FPLO) basis band structure method and optimized the equilibrium lattice parameters using LSDA total energy calculations. Relativistic LSDA produces orbital moments induced from spin polarization via spin-orbit coupling. It is found that the orbital moments of individual 3d atoms in low dimensional nanowires are very large compare to their bulk phases.

Synthesis, electronic transport and magnetic properties of Zr 1−xY xNiSn, ( x=0–0.25) solid solutions

The crystal structure of the Zr 1− x Y x NiSn half-Heusler solid solutions is synthesized and their crystal structure is determined. Electrical resistivity and thermoelectric Seebeck coefficient are measured in the 80–380 K temperature range, whereas magnetic susceptibility is measured at 290 K. It is established that substitution of Zr host atoms by Y in the ZrNiSn intermetallic semiconductor is equivalent to doping by acceptor impurities. Self-consistent ab initio calculations, based on the full potential local orbital (FPLO) minimum basis method, are performed to investigate the electronic and thermoelectric properties of these alloys. Spin polarized within the framework of the coherent potential approximation (CPA) are included.

Crystal field calculations for alloys

Abstract A new method for calculations of crystal field (CF) interaction in alloys containing rare earths (4f electron CF) has been developed. The method is based on density-functional theory (DFT) and uses the full-potential local-orbitals (FPLO) method combined with the coherent-potential approximation (CPA). The method is successfully applied to calculate the CF interaction in RENi 4 Al alloys.

Rare-earth–boron bonding and 4f state trends inRB4tetraborides

Both the basic electronic structure of tetraborides, and the changes across the lanthanide series in $R$B$_4$ ($R$ = rare earth) compounds, are studied using the correlated band theory LDA+U method in the all-electron Full Potential Local Orbital (FPLO) code. A set of boron bonding bands can be identified that are well separated from the antibonding bands. Separately, the ``dimer B'' $2p_z$ orbital is non-bonding ({\it viz.} graphite and MgB$_2$), and mixes strongly with the metal 4d or $5d$ states that form the conduction states. The bonding bands are not entirely filled even for the trivalent compounds (thus the cation $d$ bands have some filling), which accounts for the lack of stability of this structure when the cations are divalent (with more bonding states unfilled). The trends in the mean $4f$ level for both majority and minority, and occupied and unoccupied, states are presented and interpreted.

Electronic structure and magnetism of UCoGe from first principles

First-principles calculations based on density-functional theory were performed on UCoGe, a ferromagnetic superconductor reported recently [N.T. Huy, A. Gasparini, D.E. de Nijs, Y. Huang, J.C.P. Klaasse, T. Gortenmulder, A. de Visser, A. Hamann, T. Gőrlach, H.v. Lőhneysen, Phys. Rev. Lett. 99 (2007) 067006]. The electronic density of states and magnetic properties were studied using the relativistic full-potential APW plus local-orbitals method and the full-potential local-orbitals (FPLO) method, respectively. A stable ferromagnetic ground state was found. The uranium total magnetic moment is quite small (about 0.1 μ B) as a result of almost complete cancellation between the spin magnetic moment of 1.2 μ B and the opposite orbital magnetic moment of 1.1 μ B, resulting from strong spin–orbit coupling at the uranium site. A magnetic moment of 0.4 and 0.2 μ B was found at the cobalt site using the APW+lo and the FPLO method, respectively.

Fermi surface of ErGa3

AbstractThe Fermi surface (FS) in paramagnetic ErGa3 is estimated by various band structure methods: linear muffin‐tin orbital (LMTO) in the atomic sphere approximation (ASA) and three new codes contained full potential (FP) instead of ASA, namely FP‐LMTO, FP linear augmented plane wave (FLAPW), and FP local orbitals (FPLO) methods. Three dimensional (3D) electron‐positron (e‐p) momentum densities ρ (p) are reconstructed from two dimensional (2D) angular correlation of annihilation radiation (ACAR) spectra measured for paramagnetic ErGa3. Reconstructed densities in the extended p‐space, folded into the reduced k‐space, are compared with the theoretical results. Unfortunately, none of these modern FP codes is able to give satisfying description of the experimental data that are in perfect agreement with previous LMTO‐ASA results. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Ce-4f and Rh-4d electron contributions to the specific heat of [formula omitted

Ce 2 Rh 3 Al 9 has been known as a nonmagnetic heavy-fermion with a temperature dependence of a specific-heat characteristic for the non-Fermi liquids. We present the low-temperature specific heat, AC magnetic susceptibility and electrical resistivity, which display an anomaly at about 20 K. The low-temperature specific-heat data are well described by the S = 1 2 Kondo model. We found also that the low-temperature power-law behavior in the specific-heat and AC susceptibility data can be attributed to the 4f Ce electrons, whereas, the spin fluctuations due to 4d Rh electrons become pronounced at higher temperatures T > 10 K . We also investigated Ce 2 Rh 2 CoAl 9 . The specific heat clearly shows the magnetic ground state of Ce 2 Rh 2 CoAl 9 . The specific heat jump in Δ C at the temperature of magnetic ordering is strongly reduced by Kondo effect. In our linearized muffin-tin orbitals (LMTO) and full potential local orbital (FPLO) calculations both the compounds are nonmagnetic. The stability of an antiferromagnetic ground state in Ce 2 Rh 2 CoAl 9 is discussed in the Kondo-lattice limit within the model proposed by Doradziński and Spałek.