Formation Of Local Magnetic Moments Research Articles

Low-temperature thernodynamics of the Anderson model. I. Symmetric case

Abstract The thermodynamics of the Anderson model describing the formation of localized magnetic moments in a metal is presented on the basis of the exact solution. In the symmetric case a low-temperature heat capacity and magnetic susceptibility as functions of the arbitrary magnetic field are exactly calculated.

Superconductivity in Zr-3d metallic glasses

We report the results of T c and H c2 (ï) measurements in Zr 70X 30 metallic glasses. The relation between D(E F) and X is discussed in terms of recent UPS measurements. A strong depression of T c is observed for X = Fe, Mn, and Cr which we attribute to the formation of localized magnetic moments and spin fluctuations.

Formation of local magnetic moments in (V, Ti) 3S 4

The system of V 1−xTi xS 1.40 has been studied through magnetic susceptibility and NMR measurements. The Curie constant increases with quadratic dependence on the composition x within the V 3S 4 phase (0 ≤ x ≤ 0.6) and then, rapidly decreases toward the Ti 2S 3 phase (0.8 < x ≤ 1.0). The NMR absorption from V 51 nuclei with itinerant delectrons rapidly decreases with increasing Ti content in the former phase. These phenomena may indicate that local magnetic moments are formed in this system under a particular environment of vanadium atoms proposed. Metal distribution of V and Ti is also discussed.

On the origin of localized magnetic states in transition metal alloys I. Wolff model

AbstractThe generalized Wolff Hamiltonian is solved in approximations which are exact in the limit of isolated impurity. It is shown that approximations analogical to those developed by Hubbard in the narrow band Hamiltonian overestimate the effect of Coulomb correlations. The formation of localized magnetic moments is described in the selfconsistent approach, which conserves first four moments of the spectral density function. The results indicate that the degeneracy of impurity levels is essential for transition metal systems.

Model calculation of the density of states of dilute alloys

We show that the single pole dominance approximation in the theory of localized spin fluctuations gives the structure in the spectral density associated with the formation of localized magnetic moments in metals and with the Kondo effect, that is a triply peaked spectral density, in agreement with experiment.

Localized spin fluctuations

Scaling arguments and renormalization group techniques are used in the Anderson model Hamiltonian for the nonmagnetic limit of a magnetic impurity. The range of validity of the theory is limited toU/πΔ ≪ 1, where the electron-electron collisions can already compete strongly with the electron-hole collisions. A “parquet” approximation is developed; it gives for the static susceptibility in the symmetric case χ = (πΔ)−1exp (+U/πΔ). There are some hints that the exchange force might play a crucial role in the formation of localized magnetic moment. These considerations are consistent with the electron-hole symmetry in the symmetric Anderson model.

Effect of superconductivity on the formation of localized magnetic moments

The effect of the superconducting state on the formation of localized moments is investigated. It is shown that the magnetic region is slightly reduced relative to the normal state: a quantitative expression for this reduction is given.

THEORY FOR THE EFFECT OF THE LOCAL ATOMIC ENVIRONMENT ON THE FORMATION OF LOCAL MAGNETIC MOMENTS

THEORY FOR THE EFFECT OF THE LOCAL ATOMIC ENVIRONMENT ON THE FORMATION OF LOCAL MAGNETIC MOMENTS

Spin Fluctuations Associated with the Formation of Localized Magnetic Moments in Superconductors

A new theory of superconductors containing transition-metal impurities is presented, explaining the observed anomalous magnetic behavior of the impurities with quenched or nearly quenched magnetic moment resulting from the localized spin fluctuations associated with the formation of localized magnetic moments. From this theory, the superconducting transition temperatures of $\mathrm{Al}\mathrm{Mn}$, $\mathrm{Al}\mathrm{Cr}$, and $V\mathrm{Fe}$ are calculated. The puzzling "slowing down" of the decrease in ${T}_{c}$ observed for higher concentrations of transition-metal impurities is shown to arise partly from the temperature dependence of the electron scattering by the localized spin fluctuations and also partly from exchange and Coulomb coupling among the transition-metal impurities, which damp the formation of the localized magnetic moments and the spin fluctuations.

Formation of Local Magnetic Moments in Metals

Formation of Local Magnetic Moments in Metals

Formation of Local Magnetic Moments in Metals

Formation of Local Magnetic Moments in Metals

Properties of the Hyperfine Structure of Dilute and very Dilute Fe in Nonmagnetic Metallic Hosts

The Mössbauer effect has proven fruitful for investigating the magnetic properties of dilute concentrations of Fe in metals. Measurements of the magnetic hyperfine field Hhf at Fe impurities in nonmagnetic metal hosts yield information relating to the formation of localized moments and to the onset of impurity-impurity interactions. These studies fall into two classes: (A) Systems in which the impurity concentration is sufficiently low (or the measurement temperature sufficiently high) that impurity-impurity interactions play a negligible role and the Hhf depends only upon the nature of the impurity and of the host. (B) Systems in which interactions play a significant role and magnetic transitions can occur. In the first category, measurements on a number of cubic transition metals and alloys will be compared with other experimental data and with theories of the formation of localized magnetic moments. In the second category, dilute alloys of Fe with Au, and Pd will be compared with the results of other experiments and with theoretical concepts of direct and indirect exchange interactions.

Electronic Specific Heat Associated with Localized States in Actinide Metals

Motivated by the observations that the substitution of U for Th in the intermetallic compound ThAl2 results in the formation of localized magnetic moments at the uranium sites, we have made measurements of the low-temperature specific heat of a range of compounds, Th1−xUxAl2, in the temperature range 1.7° to 20°K. We have observed that the value of γ, the electronic contribution, increases with the addition of U; which increases we associate with the formation of localized 5f-like states on the U atoms and close to the Fermi energy. We calculate from the observed values of γ that the change in density of states per U atom ranges from 140 states eV−1 per U atom on the addition of 0.5 at.% U to 80 states eV−1 per U atom on the addition of 18 at.% U. That these states contribute to the specific heat indicates that they form close to the Fermi energy, a condition, within the framework of current theories, favorable to their being magnetized.