Nontransition element impurities in ferromagnetic transition metals

Effects of nontransition element impurities on the ferromagnetism of transition metals are discussed in the light of our theoretical analyses of the hyperfine interaction data of implanted nuclei which have been carried out in recent years. A detailed discussion of the effective filling of the d band by impurity valence electrons is given after presenting a brief summary of our theory of the hyperfine interaction. The change of the saturation magnetization is discussed in particular. It is pointed out that an sp valence impurity at an interstitial site in iron can increase the magnetic moments of surrounding host atoms.     

On the electronic structure of ferromagnetic transition metal surfaces

The electronic structure at the surface of ferromagnetic Ni and Fe is studied within a rigid exchange splitting model, in the tight-binding approximation. The surface resonances existing in the paramagnetic state are split. The magnetic moment is found to be the same at the surface and in the bulk in agreement with recent experiments. It is shown to be distributed almost spherically, except for (100)Ni where it points towards nearest neighbours.     

Pressure induced structural phase transition and electronic properties of actinide monophospides: Ab-initio calculations

We have investigated the structural and electronic properties of monophospides of thorium, uranium and neptunium. The total energy as a function of volume is obtained by means of the self-consistent tight binding linear muffin-tin-orbital (TB-LMTO) method within the local density approximation (LDA). From the present study with the help of total energy calculations it is found that ThP, UP and NpP are stable in NaCl-type structure at ambient pressure. The structural stability of ThP, UP and NpP changes under the application of pressure. We predict a structural phase transition from NaCl-type (B₁-phase) structure to CsCl-type (B₂-phase) structure for these phospides in the pressure range of 37.0-24.0 GPa (ThP-NpP). We also calculate lattice parameter (a₀), bulk modulus (B₀), band structure and density of states. From energy band diagram it is observed that ThP, UP and NpP exhibit metallic behavior. The calculated equilibrium lattice parameters and bulk modulus are in good agreement with experimental and theoretical work.     

Analysis of ultrafast electronic and magnetic response of ferromagnetic transition metals

Received: 23 October 1998     

Cluster calculations of the electronic structure of transition metal surfaces

The electronic structure and charge distributions for 13-atom clusters of 3d transition metals (Fe, Ni. Cu) have been calculated using a scattered wave technique. The cluster geometry is chosen to display features of stepped and flat surfaces. Many states in the band show pronounced charge lobes in the neighbourhood of edge and corner atoms, suggesting that these are active sites in these metals. These lobes are more extensive for lighter elements in the series and, for a given element, more diffuse at lower energies in the d-band. Charge expansion from the centre of the cluster to the edge atoms is a general feature, and the stepped surfaces show a variety of bonding orbitals not present on the flat surface.     

The electronic structure of some transition metal alloys

Thermal neutron scattering experiments have provided detailed information on the distributions of magnetic moment in a number of disordered ferromagnet binary alloys. The general features of these distributions together with saturation magnetization data are discussed and compared with various simple theories. Attention is focused on dilute alloy systems. After an introduction the paper is divided into four sections, the first of which deals with alloys which tend to follow the Slater-Pauling curve. Here a simple Thomas-Fermi treatment due to Friedel suggests that magnetic moment changes, largely confined to the minor constituent (solute) sites, should occur with a sign dependent on the nature of the density of states at the Fermi level in the pure major constituent (solvent). Comparison with experiment shows qualitative agreement except in the case of Fe-based alloys containing transition element solutes from the right of Fe in the periodic table. This discrepancy is examined and an explanation put forward. The next section outlines a discussion of the electronic structure of alloys of transition elements with non-transition metal solutes. The view is taken that the electronic configuration of a solute atom is roughly similar to the configuration found in the pure non-transition metal: it follows that no partially filled d orbitals are expected at solute sites. Use of a simple Thomas-Fermi model based on this assumption indicates that some of the electric screening associated with a non-transition metal solute takes place in the surrounding transition metal slovent. Additional electrons introduced in this way into the solvent occupy mainly d states and cause a reduction in magnetic properties. This reduction together with the total loss of d-state effects from the solute sites themselves can account qualitatively for the changes observed in Ni, Pd and Fe-based alloys with non-transition elements. The fourth section deals with the transition metal alloys which show marked departures from Slater-Pauling behaviour, e.g. NiCr. An explanation for these alloys has been provided by Friedel's bound impurity state model and the mechanism suggested by Comly, Holden and Low to account for the similarity in shape of the magnetic disturbances observed in different systems. The final section discusses ferromagnetic alloys of PdFe and PdCo. The giant moments associated with the Fe and Co solutes result from a widespread polarization of the Pd solvent contiguous to the solute atoms. This polarization can be interpreted with the use of a non-local exchange-enhanced susceptibility function for the Pd host. With increasing solute content this function becomes modified to an extent dependent on the shift of d holes from one spin direction to the other, i.e. on the mean polarization of the Pd.     

Solubility and distribution of substitutional impurities in ferromagnetic alloys

We investigate the solubility of a magnetic substitutional impurity and its distribution over the sites of a face centered crystallographic lattice of an ordered A-B alloy of arbitrary composition, in which ferromagnetism can occur.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 6, pp. 66–72, June, 1986.     

X-ray appearance potential spectra and electronic structure of transition metals

The possibility of determining the density-of-states distribution function in the unoccupied part of the conduction bands of the transition metals Cr, Mo and W from experimental APS spectra is considered. Comparison of the results obtained with data from band-structure calculations for these metals is carried out.     

The concentration dependence of the electronic specific heat of nearly and weakly ferromagnetic transition metal alloys

An explanation of the asymmetric peak in the electronic specific heat coefficient at the critical concentration for the onset of ferromagnetism in transition metal alloys is provided in terms of the critical fluctuations of magnetization.     

Hyperfine interaction of rare earth impurities in ferromagnetic metals

The present knowledge concerning rare earth impurities implanted in iron and nickel is reviewed. New Mössbauer spectra on the isotopes¹⁶¹Dy,¹⁶⁶Er and¹⁶⁹Tm are presented. In the case of¹⁶¹DyFe and¹⁶¹DyNi both the annealing behaviour and the temperature dependence have been studied. It is shown that in almost all cases about half of the rare earth impurities end up in substitutional sites, whereas the other part probably is associated with vacancies. The temperature dependence for these systems is in accordance with the generally accepted local moment picture, with fast relaxation behaviour on the electronic moment at the substitutional sites. For the iron host the exchange interaction dominates the cubic crystalline electric field, but for nickel both interactions are of comparable magnitude, leading to a considerable decrease of the hyperfine interaction.     

Spin fluctuations and peculiarities of semiconductor-metal electronic transitions in almost ferromagnetic compounds of transition metals

The influence of spin fluctuations on the energy spectra of sp and d current carriers in almost ferromagnetic semiconductors based on compounds of d transition metals is examined. It is shown that because electron spectra split in the fluctuating exchange fields in almost ferromagnetic systems, electronic transitions of the type semiconductor-metal are possible, accompanied by the disappearance of energy gaps in the spectra of the sp and d electrons at various temperatures and by a shift of the chemical potential into the region of allowed energies. A specific analysis of similar electronic transitions is presented, based on the almost ferromagnetic compound FeSi. Fiz. Tverd. Tela (St. Petersburg) 41, 1792–1796 (October 1999)     

Temperature-dependence of the angle-resolved photoemission in ferromagnetic transition metals

Temperature-dependence of the angle-resolved photoemission spectra in ferromagnetic metals is discussed in the light of a general picture of spin fluctuations. Calculations are made for Fe and Ni by using a local approach to the spin fluctuations and the results are compared with the recent calculation based on a long wave approximation.     

Theory of electronic structure of non-dilute transition metal alloys : Ni-Cu

The density of states for the Ni-Cu alloy system has been calculated as a function of concentration by the supercell method. This method takes into account inter-site interactions in contrast with current effective medium or single site theories. We show that the method is practical for the study of disordered systems. Comparison is made with previous work as well as with photoemission data.     

The electronic structure of bcc-based random solid solutions of transition metals

The electronic structure of Nb _x Zr_1–x , V _x Nb_1–x and Mo _x V_1–x random solid solutions with the bcc lattice structure is investigated in the frame of the first-principles tight-binding muffin-tin orbital method and the coherent potential approximation. The total and component densities of states as well as the Bloch spectral densities are determined over a broad concentration range.     

Calculated electronic structure of metallic multilayers formed by noble and transition metals

Full-potential Linearized Augmented Plane Wave calculations are performed to investigate the properties of the electronic charge of metallic multilayers formed by non-magnetic and magnetic elements (i.e. Ag, Cu and Fe). The multilayer structure is of the type A_n, A _n B _n or (AB)_n where A, B indicate Ag, Cu and Fe and n is the number of layers of the element A or B. The problem addressed by this study is the transition from the 2D behavior of the isolated monolayer to the 3D bulklike character. Therefore the calculations, carried out at paramagnetic level, illustrate the dependence of the density of states on the multilayer thickness and composition. For the three elements the main feature of the inter-layer coupling is the absence of charge intermixing and hybridization. For structures with a number of layers n? 5 the density of states bandwidth has a decrease, with respect to the bulk value, approximately proportional to the reduced coordination. At the critical thickness n = 5 and above, a noticeable difference exists between the charge in the outer layers, with reduced coordination and bandwidth, and the central layers with a bulklike density of states. Averaging between these contributions leads to the re-installment of bulklike properties. These results are in essential agreement with analytical band theories and quantum mechanical calculations for similar systems and with experiments. Received 3 October 2001     

Valence electronic structure of alkalis adsorbed on free-electron like and transition metals

Application of a simple wave function-matching technique is made to the problem of alkali adsorption on free-electron like substrates, giving in particular an estimate of the width of the resonance at a given adatom-substrate separation, which is then compared to existing first-principles calculations. The model is then applied to the alkali/transition-metal problem, thus assuming the non-importance of the transition-metal d-bands relative to their sp-bands. The results indicate a fair amount of hybridization between the ns and np valence levels of the alkali adatom.     

Character of the electronic structure of metal-like compounds of transition metals with a cementite structure

The x-ray K emission spectra in compounds of transition metals with a cementite structure show considerable similarity. The K₅ spectra of Fe, Co, and Ni in Fe₃C, Co₃B and Ni₃B and the K ₅ spectrum of manganese in (Fe_0.64Mn_0.36)₃C were studied. A joint examination of the x-ray spectral characteristics and certain physical properties shows that binding of the atoms of the metal and nonmetal in these compounds is accomplished at a high degree of fillingof the d-like bond of the valence spectrum.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 6, pp. 52–55, June, 1972.