Mesoscopic oscillations of the magnetization near Ising impurity centers in strong magnetic fields

The frequency of orientational quantum oscillations of the magnetization near impurity-ion clusters with Ising properties in a saturated magnetic crystal is calculated. It is noted that in compounds of the type Ho_xY_3−x Fe₅O₁₂, where magnetic phase transitions are observed, additional magnetization reversal and magnetic resonance features due to mesoscopic oscillations of the magnetization can be observed at low concentrations x<0.001 and cryogenic temperatures in fields comparable to the intersublattice exchange interaction field. Pis’ma Zh. éksp. Teor. Fiz. 65, No. 6, 445–448 (25 March 1997)     

Electron binding energy for heavy ions in strong magnetic fields

Within the statistical theory the analytical expression of electrostatic and exchange energies for atoms with arbitrary ionization degree in strong magnetic fields is obtained.     

Site occupancy of ferrous ions in iron garnets

Fe²⁺ site occupancy in iron garnets is investigated by means of optical absorption and magnetic circular dichroism. In particular measurements are carried out on bulk single crystals of yttrium iron garnet (YIG) doped with Si⁴⁺, Nb⁵⁺, Sn⁴⁺, Zr⁴⁺, Ti⁴⁺ and Th⁴⁺. The results are discussed in the light of the recent discovery of tetrahedral Fe²⁺ in Nb-doped YIG. We find that, in general, Fe²⁺ occupies both octahedral and tetrahedral sites, the actual distribution being related to site occupancy of the donor centers. This correlation may be relaxed by photoinduced charge transfer between iron sites, at low temperatures. Contrary to recent attributions, no dodecahedral component is found in the infrared spectra above 1 μm wavelength.     

Generation of an external magnetic field with the spin orientation effect in a single layer Ising nanographene

In this work, the magnetic properties of the single layer Ising nanogaphene (SLING) are investigated by using Kaneyoshi approach (KA) within the effective field theory for different spin orientations of its magnetic atoms. We find that the magnetizations of the SLING has no phase transition, certain Curie temperature and distinct peak of susceptibility at T_c for the some spin orientations at the zero external magnetic field (H=0.0). Because these behaviors occur at H≠0.0, we suggest that the SLING generates an external magnetic field and behaves as an external magnetic field generator for these spin orientations. However, the SLING exhibits ferromagnetic behaviors for only one spin orientations. But, it exhibits antiferromagnetic behaviors for the others. For the AFM cases, diamagnetic susceptibility behaviors and type II superconductivity hysteresis behaviors are obtained. We hope that these results can open a door to obtain new class of single layer graphene and graphene-based magnetic field generator devices with the spin orientation effect.     

Predicted existence of H 3 ++ molecular ions in strong magnetic fields

It is shown by a variational method that the molecular ion H ₃ ⁺⁺ can exist for magnetic fields B< 10¹¹ G. Pis’ma Zh. éksp. Teor. Fiz. 69, No. 11, 800–805 (10 June 1999) Published in English in the original Russian journal. Edited by Steve Torstveit.     

Diffusion of charged particles in strong large-scale random and regular magnetic fields

The nonlinear collision integral for the Green’s function averaged over a random magnetic field is transformed using an iteration procedure taking account of the strong random scattering of particles on the correlation length of the random magnetic field. Under this transformation the regular magnetic field is assumed to be uniform at distances of the order of the correlation length. The single-particle Green’s functions of the scattered particles in the presence of a regular magnetic field are investigated. The transport coefficients are calculated taking account of the broadening of the cyclotron and Cherenkov resonances as a result of strong random scattering. The mean-free path lengths parallel and perpendicular to the regular magnetic field are found for a power-law spectrum of the random field. The analytical results obtained are compared with the experimental data on the transport ranges of solar and galactic cosmic rays in the interplanetary magnetic field. As a result, the conditions for the propagation of cosmic rays in the interplanetary space and a more accurate idea of the structure of the interplanetary magnetic field are determined.     

Ising phases of Heisenberg ladders in a magnetic field

We show that Dzyaloshinskii-Moriya (DM) interactions can substantially modify the phase diagram of spin-1/2 Heisenberg ladders in a magnetic field provided they compete with exchange. For nonfrustrated ladders, they induce a local magnetization along the DM vector that turns the gapless intermediate phase into an Ising phase with broken translational symmetry, while for frustrated ladders, they extend the Ising order of the half-integer plateau to the surrounding gapless phases of the purely Heisenberg case. Implications for experimental ladder and dimer systems are discussed.     

Optical orientation of Mn2+ ions in GaAs in weak longitudinal magnetic fields

We report on optical orientation of Mn2+ ions in bulk GaAs subject to weak longitudinal magnetic fields (B≤100 mT). A manganese spin polarization of 25% is directly evaluated by using spin-flip Raman scattering. The dynamical Mn2+ polarization occurs due to the s-d exchange interaction with optically oriented conduction band electrons. Time-resolved photoluminescence reveals a nontrivial electron spin dynamics, where the oriented Mn2+ ions tend to stabilize the electron spins.     

Behavior of Ising spin glasses in a magnetic field

We study the existence of a spin-glass phase in a field using Monte Carlo simulations performed along a nontrivial path in the field-temperature plane that must cross any putative de Almeida-Thouless instability line. The method is first tested on the Ising spin glass on a Bethe lattice where the instability line separating the spin glass from the paramagnetic state is also computed analytically. While the instability line is reproduced by our simulations on the mean-field Bethe lattice, no such instability line can be found numerically for the short-range three-dimensional model.     

Atomic spin precessions of fluorine ions recoiling through vacuum in weak transverse magnetic fields

A new experimental method for unveiling the strong hyperfine interactions of multi-electron ion configurations is described. It consists in observing atomic spin precessions of nuclear-excited ions recoiling through vacuum in weak external transverse magnetic fields. Due to the strong hyperfine coupling the nuclear orientation follows the atomic precession, resulting in a rotation of the angular correlation of decayγ-rays. The method is illustrated using the long-lived 197keV¹⁹F (5/2⁺) state as probe. The observed large precessions as well as the strong attenuations of theγ-angular correlations are well accounted for by considering all possible configurations resulting from the coupling ofL-shell electrons in the relevant ionic charge states.     

Metastability of Ising spin chains with nearest—neighbour and next—nearest—neighbour interactions in random fields

One-dimensional Ising systems in random fields (RFs) are studied taking into account the nearest-neighbour and next-nearest-neighbour interactions. We investigate two distributions of RFs: binary and Gaussian distributions. We consider four cases of the exchange couplings: ferro－ferromagnetic (F－F), ferro－antiferromagnetic (F－AF), antiferro－ferromagnetic (AF－F) and antiferro－antiferromagnetic (AF－AF). The energy minima of chains of no more than 30 spins with periodic boundary conditions are analysed exactly. We found that the average number of energy minima grows exponentially with the number of spins in both cases of RFs. The energy distributions across the corresponding energy minima are shown. The effects of RFs on both the average and density of metastable states are explained. For a weak RF, the energy distributions display a multipartitioned structure. We also discuss the frustration effect due to RFs and exchange fields. Finally, the distributions of magnetization are calculated. The absolute value of magnetization averaged over all metastable states decreases logarithmically with the number of spins.     

Field-induced spin mixing in ultrathin superconducting Al and be films in high parallel magnetic fields

We report spin-dependent electron density of states (DOS) studies of ultrathin superconducting Al and Be films in high parallel magnetic fields. Superconductor-insulator-superconductor (SIS) tunneling spectra are presented in which both the film and the counterelectrode are in the paramagnetic limit. This SIS configuration is exquisitely sensitive to spin mixing and/or spin flip processes which are manifest as DOS singularities at eV=2 Delta(0)+/-eV(z). Both our Al and Be data show a well defined subgap peak whose magnitude grows dramatically as the parallel critical field is approached. Though this feature has previously been attributed to spin-orbit scattering, it is more consistent with fluctuations into a field induced mixed-spin state.     

Arrott plots of magnetic systems with strong spin fluctuations

Spin fluctuations are shown to lead to a renormalization of the coefficients in Landau theory of phase transitions and a resulting small negative curvature of Arrott plots.     

Effects of two strong fields in resonant four-wave mixing

An explicit solution is obtained for the four-wave mixing ω₄=ω₁−ω ₂+ω₃ of two strong fields E ₁, E ₃ and two weak fields E ₂, E ₄ in a four-level system with large Doppler broadening. Resonance of the intensity dependence of the mixing coefficient is found around equal Rabi frequencies, E ₁·d ₁=E ₃·d ₃, where d _1,3 are the dipole moments of the corresponding transitions. The effect is interpreted as a crossing of quasi-energy levels. Up to 6 peaks appear in the dependence of the conversion coefficient on the detuning of the probe field E ₂. The unexpected additional pair of peaks is a consequence of averaging over velocities. The results permit interpretation of the saturation behavior found in recent experiments on mixing in sodium vapor. Pis’ma Zh. éksp. Teor. Fiz. 66, No. 12, 777–782 (25 December 1997) Published in English in the original Russian journal. Edited by Steve Torstveit.     

Creation of the ordering of angular momenta of particles in strong electric and magnetic fields

It is shown that strong magnetic and electric fields can create ordered states of angular momenta, which manifests itself in the interconversion of the polarizations of radiation.     

Anisotropy of atoms in strong magnetic fields

The anisotropy of the atomic electronic density caused by strong magnetic fields is discussed here in the context of the statistical theory. In the framework of the current-density functional theory, a derivation is given of the gradient terms, necessary for anisotropy, based on the polarizability of free electrons in a magnetic field. Numerical results for the electronic density show a strong elongation of the electronic density along the field direction. In very high magnetic fields the electronic density is localized in thin columns along the field.     

Screening of impurities in strong magnetic fields

Charged impurities inserted in an electron gas in strong magnetic fields and at low temperatures are considered. Using the random phase and the generalized Born approximations, a self-consistent calculation of the screening of the impurities and the broadening of the electronic energy levels due to the scattering by these impurities is presented. Concrete results obtained in numerical form show that for typical semiconductors the anisotropy of te screening induced by the magnetic field is strongly reduced by collisional damping. The screening length, however, depends rather strongly on the field.On leave of absence from the Department of Physics, University of Tokyo, Tokyo, Japan.     

From free fields to AdS: The case of particles with spin

It is shown that one-loop diagrams with three external lines in the usual conformal field theory in D dimensions are equal to a finite sum of tree diagrams with one vertex in theory with the AdS _{D + 1} metric. Some terms of the dual Lagrangian that are responsible for interaction are calculated. Spin-0, spin-1/2, and spin-1 particles are considered.