Properties Of 3d Transition Metals Research Articles

Magnetic properties of 3d transition metals and nitrogen functionalized armchair graphene nanoribbon

First-principles density functional theory (DFT) calculations were performed to study the stability and magnetic properties of TM–CxNy (TM = Sc, Ti, V, Cr, Mn, Fe, Co, Ni, Cu and Zn; x/y = 0, 1 and 2 and x + y = 2) edge defects in armchair graphene nanoribbon (9-AGNR). The results showed that the edge functionalization of 9-AGNR by TM–N2 defects is energetically more favorable compared to the edge functionalization by TM–C2 and TM–CN defects. Furthermore, we found that edge TM–CxNy defects in 9-AGNR support high and localized magnetic moments. The magnetic moment of TMs in TM–CxNy edge defects increases with an increase in the number of unpaired electrons in the 3d orbitals, and the calculated magnetic moment is largest for an edge Mn–N2 defect. The analysis of magnetization of TMs reveals that the magnetic moment mainly comes from the electrons in the 3d orbitals and the contribution of 4s electrons to the total magnetic moment is very small. Our calculations also show that the magnetic moment of TMs in edge TM–N2 defects in AGNR is independent of edge TM–N2 defect concentrations and AGNR width in the present study. The interedge magnetic coupling between the edge TM–N2 defects is explored by investigating the competing ferromagnetic and antiferromagnetic spin structures. We found that the interedge magnetic coupling depends on the type of TMs in edge TM–N2 defects and TM–N2 edge defect concentrations.

An investigation of semiconducting behavior in the minority spin of Co2CrZ (Z = Ga, Ge, As): LSDA and LSDA + U method

We have calculated the electronic and magnetic properties of 3d transition metal based full Heusler compounds Co2CrZ (Z=Ga, Ge, As), by using full potential linearized augmented plane wave (FP-LAPW) method. The calculated density of states (DOS) and band structure for Co2CrZ shows the existence of band gap in their minority-spin channel. The respective energy gaps of Co2CrGe and Co2CrGa are 0.24 and 0.38eV with their Fermi energies (EFs) lie exactly at the gap. The compound Co2CrAs when treated with local spin density approximation (LSDA) does not show half metallic ferromagnetism (HMF) even though there exist a gap this is because the EF does not lie at the middle of the gap. We have considered Co2CrAs as strongly correlated system as Cr-d states at EF are strongly localized thus the system was treated in terms of the LSDA+U. The total magnetic moment of Co2CrAs was found to be an exact integer value 5.00μB within LSDA+U. We have also found that the total magnetic moments increase as the Z goes from Ga to As.

Site Preference and Elastic Properties of 3d Transition Metals Alloying Addition in Ductility YAg Alloys

First-principles supercell calculations based on density functional theory were performed to study the site preference behavior and elastic properties of 3d (Ti-Cu) transition-metal elements in B2 ductility YAg alloy. It is found that Ti occupies the Y sublattice, while V, Cr, Co, Fe, Ni and Cu tend to substitute for Ag site. All alloying elements can decrease the lattice parameters of Y8Ag8, among which Y7Ag8Ti shows the largest change. Furthermore, the calculated elastic constants show that Cr, Fe, Co and Cu can improve the ductility of YAg alloy, and Y8Ag7Fe presents the most ductility among these alloy, while Ti and Ni alloying elements reduce the ductility of YAg alloy, especially, V transforms ductile into brittle for YAg alloy. In addition, both V and Ni can increase the hardness of YAg alloy, and Y8Ag7V is harder than Y8Ag7Ni.

Surface properties of 3d transition metals

Using the projector augmented wave method within density functional theory, we present a systematic study of the layer relaxation, surface energy and surface stress of 3d transition metals. Comparing the calculated trends for the surface energy and stress with those obtained for 4d and 5d metals we find that magnetism has a significant effect on the surface properties. Enhanced surface magnetic moments decrease the size of the surface relaxation, lower the surface energy and surface stress, leading to compressive stress in Cr and Mn.

Transition metal induced magnetism in smaller fullerenes (Cnfor n ≤ 36)

The magnetic properties of 3d transition metals (TM) encapsulated inside smaller fullerenes ranging from C20 to C36 have been investigated using spin polarized density functional theory. The TM impurities stabilize asymmetrically at an off-center position for n≥28. The total magnetic moment (MM) of TM@Cn complexes are largely contributed by TMs and a small amount of MM of 0.12-0.50 μB is induced on the cage carbon atoms. The 3d TM atoms interact with C atoms of C20 and C28 cage ferromagnetically (FM) except for Ni@C28 which shows antiferromagnetic (AFM) interaction. The magnetic interactions change from FM to AFM in C32 cage for Ti, V, Cr and Mn. The MM gets quenched in Ni@Cn for n≥32. The total MM of Mn@Cn does not show any change although the nature of magnetic interactions changes from FM to AFM at n=32. Ti and V are the only TMs which show positive cohesive energy in all fullerenes considered. The smallest fullerene which can encapsulate all 3d TM are Cn for n≥32, consistent with available experimental and theoretical results.

Magnetic properties of 3d transition metals adsorbed on benzene: a density functional theory study

In this work, magnetic properties of 3d transition metal (TM) atoms (Fe, Co and Ni) add on benzene (Bz) molecule have been studied by means of density functional calculations. We estimated adsorption site, adsorption energy, spin and orbital moments of TM adatom and magnetic anisotropy energy (MAE) of these systems. We found that hollow sites of Bz molecule is the most stable geometry for adsorption of TM adatoms. Calculation of adsorption energy per atom confirms that TMBz molecules show high stability. Bz molecule reduces spin magnetic moment of TM adatom by a factor of two compare to their free states. The largest MAE value concluded for CoBz structure, that makes this molecule as a potential building block for long-term magnetic data storage.

First-principles study of substitutional metal impurities in graphene: structural, electronic and magnetic properties

We present a theoretical study using density functional calculations of the structural, electronic and magnetic properties of 3d transition metal, noble metal and Zn atoms interacting with carbon monovacancies in graphene. We pay special attention to the electronic and magnetic properties of these substitutional impurities and find that they can be fully understood using a simple model based on the hybridization between the states of the metal atom, particularly the d shell, and the defect levels associated with an unreconstructed D3h carbon vacancy. We identify three different regimes associated with the occupation of different carbon–metal hybridized electronic levels: (i) bonding states are completely filled for Sc and Ti, and these impurities are non-magnetic; (ii) the non-bonding d shell is partially occupied for V, Cr and Mn and, correspondingly, these impurities present large and localized spin moments; (iii) antibonding states with increasing carbon character are progressively filled for Co, Ni, the noble metals and Zn. The spin moments of these impurities oscillate between 0 and 1μB and are increasingly delocalized. The substitutional Zn suffers a Jahn–Teller-like distortion from the C3v symmetry and, as a consequence, has a zero spin moment. Fe occupies a distinct position at the border between regimes (ii) and (iii) and shows a more complex behavior: while it is non-magnetic at the level of generalized gradient approximation (GGA) calculations, its spin moment can be switched on using GGA+U calculations with moderate values of the U parameter.

Spin transport properties of 3d transition metal(ii) phthalocyanines in contact with single-walled carbon nanotube electrodes

The spin transport properties of a series of 3d transition metal(ii) phthalocyanines (MPc, M = Mn, Fe, Co, Ni, Cu and Zn) sandwiched between two semi-infinite armchair single-walled carbon nanotube electrodes are investigated by using a self-consistent ab initio approach that combines the non-equilibrium Green's function formalism with spin density functional theory. Our calculations show that among the six molecules only MnPc and FePc can act as nearly perfect spin filters and at the same time have a large transmission around the Fermi level. This is dominated by the highest occupied molecular orbital (HOMO) of the corresponding MPc molecule. In contrast to the other four MPc molecules, whose HOMO is the a(1u) orbital located over the Pc ring, the HOMO of MnPc and FePc is a doubly degenerate pi-type orbital composed of the 3d(xz) and 3d(yz) atomic orbitals of the metal center. The spin polarization of MnPc and FePc is independent of the size of the SWCNT electrodes and can be tuned by chemisorption at the metal center, demonstrating that MPc and carbon nanotubes are a promising materials platform for applications in molecular spintronics.

Magnetic properties of 3d transition metal chains on vicinal [formula omitted] surface

Density functional theory (DFT) is applied in our study to describe magnetic properties of 3d transition metal (TM) nanowires on a stepped Cu ( 1 1 1 ) surface. The basic template to study such metallic chains on the Cu ( 1 1 1 ) surface is an embedded Fe chain at one-atom distance away from the upper edge of the monoatomic surface step. Chains of 3d transition metal atoms from Sc to Ni are added on top of the Fe chain. At the beginning of the 3d row, the chains show antiferromagnetic order. A small energy difference between ferromagnetic and antiferromagnetic order is obtained for the Mn–Fe system. Cr forms an antiferromagnetic chain, whereas Fe, Co, and Ni chains are ferromagnetically coupled to the embedded Fe chain.

First-Principles Study of Magnetic Properties of 3d Transition Metals Doped in ZnO Nanowires.

The defect formation energies of transition metals (Cr, Fe, and Ni) doped in the pseudo-H passivated ZnO nanowires and bulk are systematically investigated using first-principles methods. The general chemical trends of the nanowires are similar to those of the bulk. We also show that the formation energy increases as the diameter of the nanowire decreases, indicating that the doping of magnetic ions in the ZnO nanowire becomes more difficult with decreasing diameter. We also systematically calculate the ferromagnetic properties of transition metals doped in the ZnO nanowire and bulk, and find that Cr ions of the nanowire favor ferromagnetic state, which is consistent with the experimental results. We also find that the ferromagnetic coupling state of Cr is more stable in the nanowire than in the bulk, which may lead to a higherTcuseful for the nano-materials design of spintronics.

Local electronic structure and magnetic properties of 3d transition metal doped GaAs

The local electronic structure and magnetic properties of GaAs doped with 3d transition metal (Sc, Ti, V, Cr, Mn, Fe, Co, Ni) were studied by using discrete variational method (DVM) based on density functional theory. The calculated result indicated that the magnetic moment of transition metal increases first and then decreases, and reaches the maximum value when Mn is doped into GaAs. In the case of Mn concentration of 1.4%, the magnetic moment of Mn is in good agreement with the experimental result. The coupling between impure atoms in the system with two impure atoms was found to have obvious variation. For different transition metal, the coupling between the impure atom and the nearest neighbor As also has different variation.

Strongly correlated electrons in fcc lattices

The Hubbard model was created in 1963 to study the properties of electron correlations in narrow energy bands. The intention was to model the properties of 3d transition metals. Since then, several new applications have been developed for the model. However, because of theoretical difficulties in the obtainment of its properties in three-dimensional lattices the modeling of 3d transition metals continues as a theoretical important challenge. In this work, using a grand canonical quantum Monte-Carlo method we performed an exhaustive study of the average energy ( E) as a function of the number of particles per site ( n) and of the dependence of n with the temperature ( T) for fcc lattices. We find that, for all temperatures, when the relative magnitude of the Coulombian repulsion to transfer integral ( U/ t) is of the order of 2, E has a minimum for n around 0.6. Thus, as n∼0.6 and U/ t∼2 are the known values in the literature for nickel, we show the natural applicability of a single-band model in the study of the properties of nickel.

Dielectric properties of 3d transition metal substituted BaTiO3 ceramics containing the hexagonal phase formation

The role of transition metals of the 3d series from V (Z = 23) to Zn (Z = 30) is investigated in modifying the crystallographic phase contents, microstructure and the dielectric properties of BaTiO3 ceramics containing ≤10 at% substituents. All the transition metals brought about the phase conversion to hexagonal BaTiO3 and the hexagonality is found to depend on Ba/Ti ratio as well as the processing conditions including the sintering temperature and the post sinter annealing. The er-T characteristics are modified with increasing hexagonality by way of the tremendous decrease in dielectric constant with broad and diminished emax for the mixed phase ceramics giving way to flat er-T curves for totally hexagonal specimens. Doping with >1% Zn2+ or ≥5% Mg2+ also render the ceramics completely hexagonal indicating that the crystal field effects of the 3d orbital electrons are not the cause for the conversion to hexagonal phase. Electron paramagnetic resonance (EPR) spectra of Mn-doped ceramics reveal the prevalence of defect complexes involving oxygen vacancies and different valence states of Mn occupying the Ti-sites within the corner-sharing as well as face-sharing octahedra present in hexagonal BaTiO3. EPR results also indicate defect complexes involving electron localization at Ti-sites and oxygen vacancies around the face-sharing octahedra. On annealing the ceramics in lower oxygen partial pressures at elevated temperatures leads to the reversion to corner shared (Ti3+–VO) defect complex accompanied by the conversion to cubic/tetragonal phase. The alterations in the oxygen vacancy-metal impurity defect complexes and the modifications in the oxygen close packing are the cause for the prevalence of hexagonal BaTiO3 at room temperature.

Microstructural and magnetic properties of ZnO:TM (TM=Co,Mn) diluted magnetic semiconducting nanoparticles

We have investigated the structural and the magnetic properties of 3d transition metal (TM) doped Zn1−xTMxO (TM=Co,Mn) diluted magnetic semiconducting nanoparticles for different doping concentrations (0⩽x⩽0.4) synthesized by chemical “pyrophoric reaction process.” From x-ray diffraction measurements the solubility limits of Co and Mn in ZnO nanoparticles are found to be strongly dependent on growth (calcinations) temperature (Tg). The highest solubility limit of both Co2+ and Mn2+ in ZnO at Tg∼300°C is found to be ∼30%. High resolution transmission electron microscopy studies show that Zn1−xTMxO particles are single crystalline of high quality with a wide particle size distribution in nanometric regime. The non-mean-field-like very strong concave nature of temperature dependent magnetization curves is observed at very low temperature in both the systems without showing any distinct magnetic transition. The magnetic behaviors of those Mn2+ and Co2+ doped ZnO semiconducting nanoparticles are observed to be quite different. The magnitude of net magnetization at a field of 5000Oe for Zn1−xMnxO system is found to grow with the dopant concentration (x) in sharp contrast to the case for Zn1−xCoxO where it is found to decrease. From mean field the Curie-Weiss fit as well as from the calculated values of effective exchange interaction constants (Jex), which is found to be negative, we can assert that the ground states of both of these systems are antiferromagnetic for the entire series. In the case of Zn1−xMnxO samples the magnitude of Jex is found to decrease with the increase in Mn+2 ion concentration, whereas for Zn1−xCoxO samples the magnitude of Jex is found to increase. These typical variations of Jex with antiferromagnetic interaction have been best explained through the magnetic polaron-polaron interaction model [P. A. Wolf et al., J. Appl. Phys. 79, 5196 (1996)].

Magnetic and electronic properties of lithium nitridometalates Li26(Li1$minus;xTx)N9 (T=Co, Ni, Cu)

Electronic and magnetic properties of 3d transition metal (T=Co, Ni, Cu in oxidation state +1) nitridometalates Li2[(Li1−xTx)N] were investigated. Resistivity data display an insulator–metal transition for T=Ni at x≈0.8. The effective magnetic moment per Ni-atom strongly exceeds the spin-only value at low x. This is discussed in connection with large orbital moments originating in the special surrounding of the T-ions. For higher x the magnetic moment decreases linearly towards zero which is due to delocalization during the insulator–metal transition.

Magnetic and electronic properties of lithium nitridometalates [()](=,,)

Abstract Electronic and magnetic properties of 3d transition metal (T=Co, Ni, Cu in oxidation state +1) nitridometalates Li 2 [(Li 1− x T x )N] were investigated. Resistivity data display an insulator–metal transition for T=Ni at x ≈0.8. The effective magnetic moment per Ni-atom strongly exceeds the spin-only value at low x . This is discussed in connection with large orbital moments originating in the special surrounding of the T-ions. For higher x the magnetic moment decreases linearly towards zero which is due to delocalization during the insulator–metal transition.

Transition metal impurities in 3C-SiC and 2H-SiC

The electronic and structural properties of 3d transition metal (TM) impurities in 3C-SiC and 2H-SiC have been investigated by ab initio calculations. The stability, spin states, formation and transition energies of isolated Ti, V, and Cr impurities in several charge states were computed. Our results were compared to available experimental data.

Ab initio pseudopotential study of Fe, Co, and Ni employing the spin-polarized LAPW approach.

The ground-state properties of Fe, Co, and Ni are studied with the linear-augmented-plane-wave (LAPW) method and norm-conserving pseudopotentials. The calculated lattice constant, bulk modulus, and magnetic moment with both the local-spin-density approximation (LSDA) and the generalized gradient approximation (GGA) are in good agreement with those of all-electron calculations, respectively. The GGA results show a substantial improvement over the LSDA results, i.e., better agreement with experiment. The accurate treatment of the nonlinear core-valence exchange and correlation interaction is found to be essential for the determination of the magnetic properties of 3d transition metals. The present study demonstrates the successful application of the LAPW pseudopotential approach to the calculation of ground-state properties of magnetic 3d transition metals.

Theory Of 3d Transition Metal Defects In 3C SiC

AbstractThe electronic properties of 3d transition metal (TM) defects located on one of the four different tetrahedral positions in 3C SiC are shown to be quite site-dependent. We explain the differences for the 3d TMs on the two substitutional sites within the vacancy model: the difference of the electronic structure between the carbon vacancy VC and the silicon vacancy VSi is responsible for the differences of the 3d TMs. The electronic properties of 3d TMs on the two tetrahedral interstitial sites differ even more: the TMs surrounded tetrahedrally by four Si atoms experience a large crystal field splitting while the tetrahedral C environment does not give rise to a significant crystal field splitting at all. It is only in the latter case that high-spin configurations are predicted.

STRUCTURAL AND THERMODYNAMIC PROPERTIES OF 3d TRANSITION METALS: PSEUDOPOTENTIAL THEORY REVISITED

Structural and thermodynamic properties of 3d transition metals are calculated in terms of the pseudopotential theory. The s − p and d electrons are treated in a pseudoadiabatic approximation in such a way that the s − p and d electrons are treated separately under the same footing. The s − p electrons are treated in terms of the conventional second order pseudopotential theory, while the tightly bound d electrons are treated in terms of the Wills–Harrison prescription that makes use of the Friedel rectangular electron density of states (DOS) model. The predictions of the structural phase stability and other relevant thermodynamic properties are found to be consistent with experiments for almost all of the metals.