Local Magnetic Moments In Metals Research Articles

Emergence of local magnetic moments in doped graphene-related materials

Motivated by recent studies reporting the formation of localized magnetic moments in doped graphene, we investigate the energetic cost for spin polarizing isolated impurities embedded in this material. When a well-known criterion for the formation of local magnetic moments in metals is applied to graphene we are able to predict the existence of magnetic moments in cases that are in clear contrast to previously reported density-functional theory (DFT) results. When generalized to periodically repeated impurities, a geometry so commonly used in most DFT calculations, this criterion shows that the energy balance involved in such calculations contains unavoidable contributions from the long-ranged pairwise magnetic interactions between all impurities. This proves the fundamental inadequacy of the DFT assumption of independent unit cells in the case of magnetically doped low-dimensional graphene-based materials. We show that this can be circumvented if more than one impurity per unit cell is considered, in which case the DFT results agree perfectly well with the criterion-based predictions for the onset of localized magnetic moments in graphene. Furthermore, the existence of such a criterion determining whether or not a magnetic moment is likely to arise within graphene will be instrumental for predicting the ideal materials for future carbon-based spintronic applications.

All-electron local density theory of local magnetic moments in metals

The origin of local magnetic moments in metals is investigated using a local density self-consistent supercell LMTO band method (with up to 27 atoms/cell). Results for Fe Pd agree with saturation magnetization, neutron scattering and hyperfine measurements.

Theory of localized magnetic moments in metals I finite cluster approach

The origin of localized magnetic moments formation in metals is investigated theoretically using a self-consistent local spin density molecular cluster approach. Clusters with up to 55 atoms are employed to describe isolated impurity local moment behavior in the cases of Fe Ag and Fe Pd . Densities of states and spin magnetic moments were determined and compared with results of spectroscopic (notably photoemission) and magnetization measurements, respectively. In the case of a noble metal host, the spin magnetization density is found to be highly localized around the Fe site; the iron moment is ≈ 3.9μ B and the polarization of the host Ag atoms is small. In the case of a transition metal host, the iron moment is ≈ 3.2 μ B but here the strong hybridization of the Fe-3d and Pd-4d states results in a large induced magnetic moment in the host PD metal — in essential agreement with experiment for this giant moment system.

Magnitude of localized magnetic moments in metals

AbstractThe magnitude of the localized magnetic moment of a transition or rare earth element impurity in a metal is evaluated within the framework of the Anderson model. Rotational invariance is preserved throughout. Graphs of the magnitude of the magnetization as a function of the relevant darameters of the model are provided and discussed.

Interaction between local magnetic moments in metals. II

Interaction between local magnetic moments in metals. II

Interaction between local magnetic moments in metals. I

The pair interaction between local magnetic moments in a non-magnetic metallic host is investigated within the framework of the Anderson model and the Hartree-Fock approximation. The resulting interaction reduces to the Caroli-Blandin interaction at asymptotically large distances, but differs considerably in magnitude and phase at smaller distances.

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.

Self-Consistent Treatment of the Wolff-Moriya Model

The Wolff-Moriya model for the localized magnetic moments in metals is treated self-consistently by using the decoupling method of the double-time Green functions. The resulting scattering matrix is solved exactly in the strongly correlated limit and is compared with solutions for the s-d exchange model and for the Anderson model. The expression for the resistivity differs qualitatively from those for the s-d exchange and Anderson models and can be associated with the anomaly observed in Rh-Fe alloy.

Effect of Correlation on Occurrence of Local Magnetic Moments in Metals

A new Green's function decoupling scheme has been applied to the problem of how correlation affects the occurrence of local moments in metals. Using Anderson's one orbital model, the decoupling level is above Hartree but presumably too low to include the Kondo effect. The scheme is similar to Hewson's but includes certain energy shifts which make magnetic states more likely to occur. For very weak transfer interaction between the impurity and conduction electrons, both magnetic and nonmagnetic solutions are found. The nonmagnetic state usually has lower energy in agreement with Schrieffer and Mattis and others, but when the intra-atomic Coulomb energy is sufficiently large, the magnetic solution has the lower energy. For strong enough transfer interaction the magnetic solution, of course, disappears.

Some integrals of the arctangent function

Integrals of the form f ' (tan-'cz)2nR(z)dz, where R(z) is an even rational expression in z, occur in the theory of localized magnetic moments in metals. Since integrals of this general type do not appear to be tabulated, we present here a method for evaluation as well as some interesting related material. By partial fraction decomposition all integrals of the above type may be reduced to the form

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

Electron - hole resonance in the theory of localized magnetic moments in metals

The homogeneous equation for the electron-hole Green's function of a non-degenerate impurity is solved in the Ω-approximation, using the Anderson Hamiltonian. Rotational invariance is maintained. The solution shows that a localized moment exists only in an extremely narrow range of average occupancy.

Localized Magnetic Moments in Metals

A simple model is used to obtain information about localized magnetic moments in metals from M\"ossbauer (or nuclear magnetic resonance) experiments. The formulation emphasizes the explicit dependence of the hyperfine field on the spin ${S}^{\ensuremath{'}}$ of the Fe atom and shows why the temperature dependence of the hyperfine field follows a Brillouin function of the total localized spin $S$ (with $S\ensuremath{\ne}{S}^{\ensuremath{'}}$). The moment of Fe atoms in dilute concentrations of Pd, Rh, and Mo are determined and the apparent contradiction between M\"ossbauer and susceptibility measurements for Rh and Mo is discussed.