Formation Of Local Magnetic Moments Research Articles

Magnetic Behavior of Fe Impurities in Tc and Re, and Its Relevance to the General Problem of the Magnetism of Fe in d-Band Metal Hosts.

We have observed implanted Fe ions to be nonmagnetic in the group VIIb hosts Tc and Re, by applying the in-beam perturbed angular {gamma}-ray distribution method. This result is in agreement with local spin density calculations for Fe in Tc using both supercell and single impurity approaches. The results are of key importance for a reasonable and consistent understanding of the basic, general features of local magnetic moment formation on Fe ions in transition metal hosts. {copyright} {ital 1996 The American Physical Society.}

Lattice distortion and magnetism of Fe impurity in Cu and Ag

First-principles electronic-structure calculations are performed for clusters representing an Fe impurity in the metal hosts Cu and Ag. The discrete-variational method is employed in the framework of local-spin-density theory. The host lattice distortions are taken into account in discussing the local magnetic moment formation and electronic properties. The obtained numerical results are compared with the previous theoretical and experimental studies.

Electronic band structure and magnetic effects in ternary Zr 2(Ni 1−xM x) 1 glassy alloys

The electronic and magnetic properties of the amorphous Zr 2(Ni 1−xM x) 1 alloys (M = Ti, V, Cr, Mn, Fe, Co, Ni and Cu) have investigated in the temperature range from 1.5K to 300K. As for the other Zr-3d glassy alloys (3d = Fe, Co, Cu or Ni) the temperature dependence of the electrical resistivity(T ≥ 20K) could be described in terms of the incipient electron localization. The new features are the pronounced variations of the magnetic and electron-transport properties with M. The origin of these variations are the systematic changes in the electronic band structure of the alloys on going from M = Cu towards M = Ti and the tendency to the formation of localized magnetic moments for M around the middle of 3d-series (M = V, Cr, Mn and Fe). The magnetic interactions strongly suppress the effects of the incipient localization.

Density of states and magnetic susceptibilities on the octagonal tiling

We study electronic properties as a function of the six types of local environments found in the octagonal tiling. The density of states has six characteristic forms, although the detailed structure differs from site to site since no two sites are equivalent in a quasiperiodic tiling. We present the site-dependent magnetic susceptibility of electrons on this tiling, which also has six characteristic dependences. We show the existence of a non-local spin susceptibility, which decays with the square of the distance between sites and is the quasiperiodic version of Ruderman-Kittel oscillations. These results are obtained for a tight-binding Hamiltonian with pure hopping.Finally, we investigate the formation of local magnetic moments when electron-electron interactions are included.

NMR and Susceptibility Studies of QuasicrystallineAl-Mn-Si-Ru Alloys

Magnetic susceptibility and nuclear magnetic resonance measurements have been made on quasicrystalline and crystalline phases of Al 62 Mn 20 Si 10 Ru 8 and Al 68 Mn 20 Si 6 Ru 6 alloys. The average value of local magnetic moment on Mn atoms and the spin-glass freezing temperature are not different so much between the two phases. However, static and dynamical properties of 27 Al NMR signals observed in the two phases are significantly different. These results suggest that most of the magnetic properties such as the formation of local magnetic moments and the magnitude of interactions between them are not closely related with the presence or absence of translational symmetry of the lattice; these properties might be related with local atomic configuration. A characteristic property of electrons in the present quasicrystals has been demonstrated by the transferred hyperfine interactions between Mn atoms and Al nuclei.

ON THE SUBSTITUTION OF Zn FOR Cu ATOMS IN HIGH‐Tc SUPERCONDUCTORS: EPR MEASUREMENTS OF La1.82Sr0.18(Cu1‐xZnx)O4

EPR measurements of La1.82Sr0.18 (Cu 1−x Zn x )O4 compounds reveal that Zn doping induces formation of localized magnetic moments which, as has been found here, sit on Cu ions. At Zn concentration of 1 atomic percent, the quantity of these magnetic moments is close to the amount of substituted ions. This result is important for verifying diverse microscopic mechanisms of high‐T c superconductivity.

Disorder and interactions in the Hubbard model.

We investigate the single-band Hubbard model with random site energies in the strong-repulsion limit, as represented by the slave-boson formulation of the t-J model. It is essential to include the correlations between the slave-boson mean field and the disorder. This leads to the widening of the non-Fermi-liquid (``generalized Mott insulating'') region around half filling. In the Fermi-liquid regime we apply the renormalization-group method. The resulting phase diagram has superconducting, magnetic, and insulating phases. The disorder generally suppresses superconductivity and gives rise to the formation of localized magnetic moments.

NQR and spin-lattice relaxation of 63Cu in radiation disordered YBa 2Cu 3O 6.95

We report on NQR spectra and the spin-lattice relaxation rate of 63Cu in YBa 2Cu 3O 6.95 ceramic samples, irradiated by a fluence of fast neutrons ( F = 0–2 × 10 19 sm -2). The formation of localized magnetic moments at the Cu(2) position was found under disordering. An evaluation of magnetic excitation spectra monitoring the spin lattice relaxation process at Cu atoms of irradiated samples is discussed.

Magneto-Volume Effects in the Weak Itinerant Ferromagnets on the Basis of Solid Solutions of Fe1−yMnySi and Fe1−xCoxSi

Peculiarities of formation of temperature-induced local magnetic moments and their influence on magneto-volume effects in weak itinerant magnets of Fe1−yMnySi and Fe1−xCoxSi are studied. The obtained results of the measurementof magnetic susceptibility and thermal coefficients of linear expansion are discussed in the framework of spin-fluctuation theory. [Russian Text Ignored].

Pair breaking effects of atomic disorder induced in YBa 2Cu 3O 7 by electron irradiation

Irradiation effects of electrons at very low temperatures ( T irr <40 K, 2.7 MeV) on the DC-susceptibility χ DC above T c of YBa 2Cu 3O 7 have been studied by means of a SHE SQUID magnetometer. Contrary to nonirradiated stoichiometric samples which have a nearly temperature independent paramagnetic susceptibility, χ DC, between 100°C and 300°C, specimens irradiated with doses of 4 × 10 19 e -/cm 2 show a distinct Curie-type behaviour due to the formation of local magnetic moments, superimposed on a temperature independent part. By annealing up to temperatures of 500 K recovering of the Curie-type contribution takes place in a similar way as that of T c. The Pauli susceptibility remains constant during irradiation, indicating that there is, contrary to A15-superconductors, no significant reduction of the density of states at the Fermi level. The correlated annealing of T c and of the Curie constant suggests a magnetic pair breaking mechanism due to radiation induced local magnetic moment.

Local magnetic moment formation of Fe ions in sp-band metal hosts.

Spin and orbital magnetism of Fe ions in $\mathrm{sp}$ metals are reduced simultaneously from stable ionic ${\mathrm{Fe}}^{2+}$ to nonmagnetic behavior with increasing lattice pressure. The various data and interpretations of the host and temperature-dependent susceptibilities, of $3d$ spin dynamics, and of crystal fields of Fe ions in $\mathrm{sp}$ metals provide a new critical test of models on moment formation, $d\ensuremath{-}\mathrm{sp}$ exchanges, and the Kondo effect of $3d$ ions in $\mathrm{sp}$ metals. Fe in $\mathrm{sp}$ metals reflects basic features common to certain $4f$ systems, but with qualitative differences from the magnetism of Fe in noble metals.

Superconductivity and magnetism in transition-element-substituted YBa2Cu3O7 compounds

Superconducting properties of YBa2Cu3O7 have been investigated by a systematic substitution of 3d transition elements for 10% of the Cu ions. Early transition elements Ti, V, and Cr affect the superconducting temperature of YBa2Cu3O7 only slightly. Local magnetic moment formation is observed in Mn, Fe, Co, and Ni substituted compounds. Tc strongly correlates with the size of the paramagnetic moments, possibly due to scattering from the magnetic sites. Zn displays a phenomenal ability to suppress Tc because of the elimination of the 3d holes. The Zn compositional dependence of Tc indicates that the superconductivity completely disappears at 13–14 at. % of Zn. It is suggested that Zn preferentially substitutes the Cu(2) sites.

Temperature-induced local magnetic moments (TILMM) in monosilicides of 3d transition metals

Features of the formation of temperature-induced local magnetic moments (TILMM) and their influence on the magnetic and thermophysical characteristics of iron, cobalt, and manganese monosilicides are investigated. The results obtained for magnetic susceptibility and specific heat measurements are discussed within the framework of spin-fluctuation theory. Temperature-concentration dependences are established for the TILMM absolute value for mutual solid solutions Fe1−xCoxSi and Fe1−yMnySi. It is shown that for a number of the alloys studied the saturation of the TILMM absolute value does not occur, while the anomalous behavior of the polytherm of their physical properties is associated with features of the band structure.

Formation of large local magnetic moments at the Cr/Au(100) interface: Evidence for a diffuse interface.

Formation of large local magnetic moments at the Cr/Au(100) interface: Evidence for a diffuse interface.

Superconductivity in amorphous Cr films

Superconducting transition has been observed for the first time in amorphous Cr films prepared by co-sputtering of Cr and BN. Superconducting transition temperatures ( Tc) up to 1.14 K have been observed with an orbital contribution (i.e.(d H c2⊥ /d T) Tc ) as large as 49 kOe K -1. The electronic specific heat coefficient (γ) has been estimated to be about 1.6 times as large as that of amorphous Mo-BN (or Mo-metalloid) alloys. This finding, i.e. the low Tc with the large γ for amorphous Cr is inconsistent with data reported for amorphous alloys of 4 d and 5 d transition elements. This inconsistency implies a formation of local magnetic moments or spin fluctuation in the amorphous Cr film.

NMR and Susceptibility Studies of Al80Mn20Quasicrystal

The temperature dependences of NMR spin-echo spectrum and magnetic susceptibility have been measured in the quasicrystalline phase of Al 80 Mn 20 . Compared with the equilibrium crystalline (hexagonal) phase, the susceptibility shows a marked temperature dependence below about 100 K. The widely distributed and temperature dependent NMR spin-echo spectrum has been observed only for the Al sites with a characteristic line shape at low temperatures that we tentatively attributed to a spin-density-wave like random distribution of the local fields at the Al sites. The lack of NMR signal associated with the Mn sites and the temperature dependence of the susceptibility suggest the formation of local magnetic moments on the Mn sites in the quasicrystalline phase.

ESR study of local magnetic moment formation, annihilation and relaxation in iodine-doped polyacetylene

ESR and conductivity measurements on iodine-doped (CH) x are reported, providing evidence for (a) a dramatic decrease of the number of localized spins with increasing temperature and conductivity, (b) a completely different behaviour of the linewidth vs. temperature for cis and trans doped samples, and (c) a relatively large longitudinal relaxation rate which increases upon increasing the temperature. A model involving the formation of localized magnetic moments and delocalization by hybridization effects can qualitatively account for these observations.

Correlation Effects in the Rotationally Invariant Asymmetric Anderson Model

AbstractThe asymmetric single orbital Anderson model is examined in the contextof formation of localized magnetic moments. Full rotational invariance is preserved in a treatment which completely includes d—d correlations and is perturbative in the hybridization parameter V. Finite values for the host bandwidth B are considered. Physical quantities such as the average occupation number of local electrons, spectral density functions, and the mean square value of the magnetization are evaluated for the single‐occupied ground state of this system at zero temperature and for general asymmetry. These quantities are found to be continuous functions ofthe model parameters. It is argued the strongly asymmetric case, relevant for mixed valence situations, is hard to reach. Numerical results are given in the weak coupling asymmetric regime and compared to other variational approaches.

Formation of Local Magnetic Moments of Ce in Metallic Elements

The local susceptibility of extremely dilute Ce ions recoil implanted into more than thirty metallic elements is microscopically observed by perturbed angular $\ensuremath{\gamma}$-ray distribution techniques. Many elements in which the single Ce ion reflects intermediate or even nonmagnetic behavior have been found. These results allow correlation of the magnetic Ce-ion behavior with matrix-dependent quantities.

Superconductivity and the electronic structure of Zr- and Hf-based metallic glasses

The results of a comprehensive study of the superconducting transition temperatures of Zr- and Hf-based metallic glasses are reported. The microscopic origins of superconductivity in these glasses are discussed in terms of recent ultraviolet photoelectron spectroscopy (UPS) measurements and calculations based on the renormalized atom technique. These calculations accurately predict the UPS spectra and the results of low-temperature heat-capacity measurements. The complete description of the electronic structure afforded by these calculations allows, for the first time, a consistent picture of the variation of Tc with X in the glasses Zr1-yXy (X=3d or 4d transition metals). In addition, the dependence of Tc with composition (y) can be understood in terms of the X d subband positions relative to EF. The results reported here support our recent contention that the strong depression of Tc observed for X=Fe, Mn, Cr, and V glasses is related to the formation of localized magnetic moments and spin fluctuations. An alternate explanation for the low Tc of X=V and Cr glasses based on the idea of an atomic-structure change is also discussed.