Indirect interactions between localized magnetic moments in doped semiconductors

The coupling between localized magnetic moments via conduction electrons is calculated taking into account the temperature and the mean free path of the electrons. For a fully degenerate electron gas and an infinite electronic mean free path the oscillatory RKKY interaction is obtained. On the limit of Boltzmann population and for infinite electronic mean free path the interaction can only be ferromagnetic. Taking into account the electronic mean free path the possibility of antiferromagnetism is restored. Furthermore the range of the interaction decreases. Several intermediate cases and possible applications are discussed.     

Indirect interaction of the localized magnetic moments

The methods of the indirect interaction operator derivation for the quantum particles locally coupled with the quasi-particles of another physical subsystem are reviewed. A variant of the consecutive canonical transformations method which allows one to obtain a nonperturbative solution of the problem is proposed for the systems which do not contain Fermi particles.     

Giant magnetic moments in dilute magnetic semiconductors

The concentration dependence of the specific magnetic moment value at room temperature in dilute semiconductor titanium oxides doped with either Co or Fe has been investigated. This value was found to increase sharply at small concentrations of magnetic impurity. The magnetic moment of 22.9 μ_B per impurity atom has been revealed for TiO₂ doped with 0.15 at% Co, not yet reported in any semiconductor oxide systems. We conclude the observed giant magnetic moments are caused by the crystal lattice polarization at small impurity concentrations. The comparison with published data point to different types of the magnetization concentration dependence for various semiconductor matrixes that is probably related to the dielectric permittivity of the environment.     

Giant magnetic moments in ferromagnetic oxide semiconductors

Concentration dependence of the specific magnetic moment of Co-and Fe-doped titanium oxide semiconductors has been studied at room temperature. A sharp increase in the magnetic moment has been found at low concentrations of a magnetic impurity. A giant value of 22.9 μ_B per impurity atom has been detected in TiO₂ with a Co concentration of 0.15 at %, which has never been observed in oxide systems. The giant magnetic moments observed at low impurity concentration are attributed to the polarization of a crystal lattice. Comparison with the literature data indicates that the concentration dependences of magnetization are different in different oxide matrices.     

Magnetic interactions in a classical system of charged particles with intrinsic magnetic moments

A classical, quasirelativistic Hamiltonian is found for a system of charged particles with intrinsic magnetic moments. It represents a generalization of the Darwin Hamiltonian and is the classical analog of the Breit Hamiltonian.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 11, pp. 73–76, November, 1973.     

Motional enhancement of exciton magnetic moments in zinc-blende semiconductors

We report a remarkable enhancement of the magnetic moments of excitons as a result of their motion. This surprising result, which we have observed in magneto-optical studies of three distinct zinc-blende semiconductors, GaAs, CdTe, and ZnSe, becomes significant as the kinetic energy of the exciton becomes comparable with its Rydberg energy and is attributed to motionally induced changes in the internal structure of the exciton. The enhancement of the magnetic moment as a function of the exciton translational wave vector can be represented by a universal equation.     

Effect of cyclotron resonance on the indirect exchange between localized magnetic moments

The effect of the simultaneous presence of an electromagnetic and a D.C. magnetic field on the magnon dispersion relation is discussed within the s-d-model. It is found that as the radiation frequency approaches the electron cyclotron frequency there is a quenching of the carrier contribution to the spin wave dispersion equation.     

Magnetic interactions between vacancy-induced intrinsic magnetic impurities in single-wall carbon nanotubes

Spin-half paramagnetism induced by point detects was found in graphene recently,micromechanism of this magnetic response can be explained well by the intrinsic magneticimpurity theory. In this paper, we apply this theory to two types of single-walled carbonnanotubes (SWCNs) and calculate the properties of various magnetic interactions forcomparison. Interestingly, magnetic interactions have different behaviors in thesesystems. Following our calculation, within a short length, the interactions can besuppressed by ether size effect or a tiny band gap, and then exhibit exponentiallydecaying. However, in the absence of a band gap, the RKKY interaction could leave a tinytail at long range, which determines long range magnetic order. Further more, when a tinyband gap exist in the systems, the Heisenberg coupling is the dominate one due to theexpanded wavefunction. According to these result, vacancy states in different types ofSWCNs could form different magnetic order, bringing abundant candidates forapplication.     

Another approach to localized magnetic moments in the Hubbard model

By using the band part of the Hubbard Hamiltonian as our starting point, we find that for one electron/atom, with Coulomb repulsion U and bandwidth Δ, there is a single band with sharp Fermi surface and enhanced Pauli paramagnetism for U < Δ, and a splitting into two symmetric bands with local moment formation for U > Δ.     

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$\text{Ag}$ and Fe$\text{Pd}$. 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.     

Theory of magnetic susceptibility of Bloch electrons: Effect of localized magnetic moments

We derive for the first time a first-principles theory of the magnetic suceptibility (χ) of Bloch electrons including the effects of periodic potential, spin-orbit interaction and localized magnetic moments, and believe it to be the most general and thorough treatment which has yet been made of this problem. The importance of the theory in possible applications is discussed.     

Indirect exchange interaction in semiconductors

We study theoretically the nature of the indirect exchange interaction between localized moments in a semiconductor, mediated by the spin-dependent spatial polarization of the valence band electrons. The interaction drops off exponentially with the inter-spin distance and the decay constant depends on the energy gap and carrier effective masses. The sign of the interaction is ferromagnetic within our simplified model but could be reversed for some more complicated band edge structures.     

Interaction between localized moments in dilute alloys: Correlation effects

The effect of including dynamical correlations between electrons of opposite spins in determining the ground state energy of a pair of magnetically interacting impurity atoms in an otherwise normal metal is discussed. It is found that in the ground state of such a system the spins of the magnetic impurity atoms are aligned antiparallel. In other words, the interaction between the localized states is of antiferromagnetic exchange type. This result differs sharply from that predicted by the Hartree-Fock (H-F) theory, in which the ground state of the system can be either ferro- or antiferromagnetic, depending on the energies of the spin up and spin down electrons relative to the Fermi energy. The calculations are performed using many-body Green's function techniques in thet-matrix approximation.     

Analysis of some magnetic properties of diluted magnetic semiconductors including long-range interactions

Specific heat, susceptibility and magnetization of four diluted magnetic semiconductors (Cd_1−xMn_xTe, Cd_1−xMn_xSe, Hg_1−xMn_xTe and Hg_1−x^- Mn_xSe) are analysed with a model which includes long-range interactions. Calculations based on an extended version of a nearest neighbour pair approximation yield a fair agreement with the experimental data. No adjustment of the statistical distributions of magnetic ions is found to be necessary.     

Antiferromagnetic interactions between localized states in amorphous germanium

The temperature dependence of the magnetic susceptibility (300 → 1.6°K) and ESR (300 → 6°K) of amorphous germanium have been determined. There is a temperature dependent paramagnetic term to the magnetic susceptibility due to a density of localized unpaired spins (dangling bonds) of 10¹⁹ spins/cm³. There is an antiferromagnetic interaction between at least some of these localized unpaired spins with an exchange energy estimated by various models to be on the order of a degree Kelvin.     

Electron affinity for intrinsic semiconductors

An approach for estimating the electron affinity using the method of dielectric formalism is developed. It is shown that the volume component of the electron affinity is related to the formation of exchange-correlation holes in the valence band. The interaction of an electron with this hole on the surface is responsible for the surface component. The relation obtained agrees satisfactorily with the rather meager experimental data available for semiconductors, and enables the electron affinity to be estimated for polycrystalline semiconductors for which there is no reference data. The calculation is carried out for 14 well-known semiconductors. In the case of metals, the relations obtained give the work function of the electron, which agrees, with a relative error of up to ±30%, with experimental data for the majority of elements.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 9, pp. 76–80, 1982.     

Bifluctuon,localized on an impurity center in magnetic semiconductors and binary solid solutions

The possibility of localization of a bifluctuon near an impurity center in ideal paramagnetic semiconductors and ideal solid solutions with equal concentrations of both components is investigated. Calculations with symmetric and antisymmetric wave functions showed that in solutions the studied formation is energetically favored for all values of the energy of exchange interaction of electrons with the concentration nonuniformity and the energy of coulomb attraction of electrons to the center, while in magnets it is energetically favored only for large values of the atomic spins and in a not very wide temperature interval.Kiev Polytechnical Institute dedicated to the Fiftieth Anniversary of the Great October Socialist Revolution.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 8, pp. 10–15, August, 1988.     

On the behavior of localized magnetic moments in liquid Cu-Al(Fe) alloys

The magnetic properties of dilute Cu-Al alloys with 5 at.% Fe were measured in the solid and liquid states. The results are compared to the Scalapino formula for the susceptibility of dilute alloys. The transition from the magnetic to the non-magnetic state was observed at 41.5 at.% Al.