Ferromagnetic Transition Metals Research Articles

Spin-polarized Auger-electron spectroscopy.

A comprehensive review of spin-polarized Auger-electron spectroscopy on 3d transition-metal ferromagnets is presented. The kind of information obtained from the Auger-electron spin polarization depends on the particular transition involved. Decays with emission of a valence electron probe the local magnetization at the site where the transition occurs. Particularly, the super-Coster-Kronig ${M}_{23}$${M}_{45}$${M}_{45}$ transitions are well suited for monitoring magnetic behavior with elemental resolution. Details of the spectra are sensitive to screening and electron correlation effects as illustrated by a comparison between Fe and Ni. Furthermore, core-hole-only decays\char22{}as exemplified by the ${L}_{3}$${M}_{23}$${M}_{23}$ process\char22{}yield exchange-interaction strengths between partly filled shells on a single atom.

Hyperfine magnetic fields at rare-earth elements in ferromagnetic transition metals

Hyperfine magnetic fields for such probes as:152SmFe,152SmCo,152SmNi,155GdFe,172YbFe,172YbCo and172YbNi have been measured using PAC method. The quantitative analysis of components of these fields has been also performed.

High-pressure and high-temperature electrical resistivity of ferromagnetic transition metals: Nickel and iron.

In this paper we report high-pressure and high-temperature electrical resistivity measurements on nickel and iron. It is observed that in nickel, the pressure coefficient of electrical resistivity changes sign and magnitude across the magnetic transition. The pressure coefficient of electrical resistivity for iron is normal and is almost independent of temperature. In nickel, the data analysis indicates that the temperature derivative of the electrical resistivity goes through a minimum at 20 kbar, which could be connected to the band-structure change and to a second-order transition. By invoking the idea of the exchange version of Baber scattering operative in paramagnetic nickel, we are able to account for the anomalous behavior of the pressure coefficient of electrical resistivity.

Singular volume dependence of transition-metal magnetism.

The transition from nonmagnetic to magnetic behavior in transition-metal ferromagnets is studied by analysis of all possible volume evolutions of the variation of the total energy with magnetic moment. In contrast to a large body of previous work, magnetic transitions are shown to be necessarily singular, and usually multivalued and discontinuous. Self-consistent spin-polarized energy-band calculations for bcc nickel, fcc cobalt, bcc vanadium, and fcc iron are presented as examples supporting and illustrating the general conclusions.

The spin wave excitations and the temperature dependence of the magnetization in iron, cobalt, nickel and their alloys

A critical review is given on the literature concerning spin waves in the ferromagnetic transition metals and their alloys. It is shown that spin waves can account for the low temperature behaviour of the magnetization in metallic glasses as well as in nickel(-alloys). A systematic correlation between Curie-temperature and spin wave stiffness is worked out, holding for crystalline and amorphous alloys of iron, cobalt and nickel. The reduced magnetization versus temperature curves of (amorphous) alloys are interpreted without referring to disorder effects.

Self-consistent model of hydrogen chemisorption on ferromagnetic transition metals.

The chemisorption of hydrogen on ferromagnetic transition metals is studied self-consistently with use of a spin-dependent Anderson-Hubbard Hamiltonian. The electronic structure of the crystal is treated with the Bethe-lattice method. The present treatment differs from previous ones in that the dominant effects of the change in occupancy of the substrate orbitals are taken into account. The consequent modification of the substrate Hamiltonian leads to the result that the chemisorption energy changes very little with the change of the magnetization of the substrate. This finding agrees with recent experimental evidence that a magnetic phase transition has no influence on the catalytic activity.

The surface spin waves in the multiband model

The transverse dynamic susceptibility in thin films of ferromagnetic transition metals is calculated within the framework of the approach used by Lowde and Windsor for bulk crystals. Numerical calculations are carried out using the band structure determined in a self-consistent way according to the LCAO method. The changes of the effective Coulomb integral and of the atomic potential in the surface layers are taken into account. For wave vectors small as compared to the reciprocal lattice vector the well-defined surface spin waves with energies lower than energies of bulk modes are obtained. For greater values of the wave vector the spin wave modes are rather strongly damped.

Spin waves in ferromagnetic transition metals. I. General formalism and application to nickel and its alloys

A new formula is derived for the spin-wave stiffness constant D and is compared with previous work. It is shown that in NiD is very sensitive to the 'ground-state' exchange splitting Delta in the d band and that hybridisation with the sp band has little effect on D. The observed value of D yields a value of 0.40 eV for Delta , which is larger than the observed quasiparticle exchange splitting of 0.33 eV, as expected theoretically. Calculations on D in Ni alloys, within the virtual crystal approximation, are compared with experimental results on NiCo and NiFe.

Spin waves in ferromagnetic transition metals. II. Iron and its alloys

For pt.I see ibid., vol.15, p.2339 (1985). The formula for the spin-wave stiffness constant D derived in the preceding paper is applied to Fe and its alloys. It is found that D in pure BCC Fe is sensitive to details of the band structure and that hybridisation between d and sp electrons is essential to secure proper stability of the ferromagnetic ground state. Starting with a band structure which gives a value of D for pure Fe in agreement with experiment, the authors use the virtual crystal approximation to calculate the variation of D with composition in alloys of Fe with Ni, Co, Mn, Cr, and V. The agreement with experiment is generally good.

Icosahedral order in glass: Electronic properties.

Icosahedral short-range order in glass is modeled by a crystalline packing of atoms in ${S}^{3}$, known as polytope 120. We diagonalize realistic electronic Hamiltonians using the symmetry group of polytope 120. We predict band structures for amorphous semiconductors and transition metals. Icosahedral order in silicon produces a gap in the center of the valence band. The absence of d-level splitting at the center of the Brillouin zone distinguishes icosahedrally ordered transition metals from their fcc counterparts. We use the d-band density of states of polytope 120 to understand band ferromagnetism in amorphous transition metals.

Spin-Polarised Energy Bands for MnPt3, FePd3and PtFe3

The electronic energy band structure for MnPt 3 , FePd 3 and PtFe 3 , which are a typical ferromagnetic transition metal alloy having the AuCu 3 -type crystal structure, is calculated by a self-consistent, spin-polarised APW method with the local-spin-density approximation. The relativistic effects except the spin-orbit interaction are taken into account. A fairly large exchange splitting, about twice that of the Fe metal, is found to occur in the Mn and the Fe d bands of these alloys. Calculated results for the density of states and the spin magnetic moment of each constituent atom agree quantitatively well with recent experimental results.

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.

Spin-wave impurity states in metallic ferromagnets

It is shown that spin waves in dilute ferromagnetic transition metal alloys can be described in terms of effective matrix-matrix and impurity-matrix exchange integrals. Such a parametrization is exact within the random phase approximation for long-wavelength spin waves. The effective impurity-matrix exchange integral is determined in the tight-binding approximation in terms of the impurity potential and local density of states. The present theory is applied qualitatively to NiFe alloys.

Itinerant magnetism in metallic glasses

Abstract It is argued that when a ferromagnetic transition metal T (e.g. Fe) is mixed with a metalloid M to form a metallic glass (having a narrow band of conduction electrons) the competing effects of the 3- d intra-atomic Coulomb repulsion and of the interaction between conduction and d -electrons make the magnetic moment of T -atoms to vanish when the concentration x of T -atoms is smaller than a critical concentration x c . Experimental data for the magnetic moment of iron atoms in Fe x B 1- x is analyzed along this line and a satisfactory fit is obtained. Inclusion of structural as well as compositional disorder effects could result in a better agreement between theory and experiment.

Correlation effects in ferromagnetism of transition metals

The effect of electronic correlations on the ferromagnetic instabilities, effective local moments, and fluctuations in spin and charge in a transition metal is discussed with a model Hamiltonian which includes intraatomic Coulomb and exchange interactions. The one-particle properties of $d$ electrons are described by bcc and fcc canonical bands. We find that reduction of density fluctuations and formation of local moments change the Stoner criterion and the condition for the ground state to be completely ferromagnetic. The magnetic states of Fe, Co, and Ni are studied in more detail, where the electrons are found to be considerably correlated for realistic model parameters. Redistribution of electrons between the ${e}_{g}$ and ${t}_{2g}$ states seen there causes deviations from the Stoner theory and is responsible for different exchange splittings of both types of states. The results are in qualitative agreement with the experimental data and suggest the use of anisotropic exchange correlation potentials in transition metals.

On the possibility of observing paramagnons in transition metals

A possible tunneling experiment to reveal the specific features of the paramagnon spectral in nearly ferromagnetic transition metals is proposed.

Analysis of Magnetic and Non-Magnetic Surfaces by Spin-Polarized Low-Energy Electron Diffraction

A survey is given of most recent progress in harnessing electron spin polarization for the study of crystalline surfaces by low-energy electron diffraction (LEED). Spin-polarized LEED from non-magnetic surfaces has been extended both experimentally and theoretically to low-Z surfaces, for which spin-orbit coupling is weak, to adsorbate systems, and to very low energies, where fine structure effects associated with the surface potential barrier are prominent. For ferromagnetic transition metal surfaces, measurement of the exchange-induced scattering asymmetry has revealed the surface Curie temperature and the critical exponent of the surface magnetization. At lower temperature, comparison with corresponding calculated exchange asymmetry profiles has successfully been employed for the determination of the layer dependence of the magnetization in the surface region.

MAGNETIC DIFFUSE SCATTERING MEASUREMENTS USING POLARISED NEUTRONS

Two distinct polarised neutron techniques are applicable to the study of magnetic diffuse scattering. The first, used for ferromagnetic alloys, employs a polarised incident beam without analysis of the outgoing polarisation. This method has been widely used, chiefly by the Oak Ridge group, to study moment disturbances in ferromagnetic binary transition metal alloys. The second technique involves polarisation analysis and has been used to study spin correlations in concentrated spin glass materials, and moment defects in antiferromagnetic alloys. Measurements on antiferromagnetic γ-Mn alloys show that the usual assumption of a collinear moment defect is not valid. The spin correlations in certain concentrated spin glass alloys are found to have an incommensurate modulation. This may result from the modification of the antiferromagnetic couplings by the atomic correlations in the alloys.

Strong short range magnetic order in ferromagnetic transition metals above Tc: A theoretical explanation

A theory for the existence of strong short range magnetic order in itinerant magnetism above T c is presented. We derive a characteristic lengthscale for short range order, given by the square root of bandwidth over k B T c . This is of order 20 Å in the ferromagnetic transition metals.

Self-consistent model of hydrogen chemisorption on ferromagnetic transition metals

Self-consistent model of hydrogen chemisorption on ferromagnetic transition metals