Equilibrium concentration of lattice vacancies in magnetic alloys with interstitial atoms

In this paper we have studied the simultaneous influence of interstitial atoms, magnetic ordering and atom ordering on the equilibrium concentration of lattice vacancies in binary alloys with body centered lattice of -brass type. In the course of calculation we took into account the interaction between nearest neighbouring atoms and we neglected correlations between atoms.     

Effect of orbital degeneracy on the magnetic phases of manganites in the electron doping region

The carrier electronic spectrum E(k) calculated with inclusion of orbital degeneracy of the manganese e _g band for the main types (A, G, and C) of antiferromagnetic ordering in La_1-y Ca_yMnO₃ was employed to derive the total energies of various magnetic configurations for the electron doping region y>0.5. To find the magnetic configuration with the minimum total energy, this energy was minimized with respect to the angle between the spins of Mn⁴⁺ ions belonging to two different magnetic sublattices. The manganite phase diagrams obtained in this way for T=0 K depend on the Heisenberg interatomic exchange parameter J _AF and the intra-atomic Hund exchange J _H and fit correctly to the available experimental data. The calculations show that if the e _g-level splitting is taken into account, there is no magnetic-sublattice canting for equilibrium A and C phases in the region of realistic values of the parameters 0.012<J _AF/t<0.02 and J _H/t=1.7. Transition to the ferromagnetic state through the double-exchange mechanism is energetically favorable only for the G phase with increasing electron concentration. However, already for x≤0.1, the collinear phase C becomes dominant and this transition does not occur.     

Coherent population trapping states with cold atoms in a magnetic field

Using potassium atoms cooled with a MOT, ground-state hyperfine coherent population trapped (CPT) states were prepared in a magnetic (B) field, and the behavior of CPT states was experimentally studied. We carefully measured the preparation of the CPT state as a function of time and the CPT signal as a function of laser power. The experimental CPT signal linewidth was approximately proportional to the square root of laser intensity in the range of parameters studied, and limits of this relation were explored theoretically.     

Equilibrium orientation states in a system of two magnetic layers with antiferromagnetic coupling

The equilibrium orientations of magnetic moments are found for a system of two antiferromagnetically coupled magnetic films in an external magnetic field. Field intervals are found where the noncollinear and orientational bistability states occur, resulting in the orientation hysteresis and phase transition.     

Magnetic and orbital structures of manganites in the electron doping region

Total energies of various magnetic and orbital configurations of the La_1?yCa_yMnO₃ manganites were calculated for the electron doping region y>0.5 with inclusion of the manganese e_g level splitting. The state of the system was first established by total energy minimization in both the angle between the spins of neighboring Mn⁴⁺ ions and the two orbital-mixing angles defining the type of ordering in the system under study. The manganite phase diagrams constructed for T=0 correctly reproduce the alternation of magnetic orbitally ordered structures, which is experimentally observed to occur with increasing electron concentration in the region of actual values of the Heisenberg interatomic exchange parameter, the Hund exchange parameter, and the hopping integral.     

Phase transitions in manganites with substitution of divalent ions for manganese

Experimental data are presented for the position of phase boundaries “orthorhombic-rhombohedral structure” and “semiconductor-metal” in manganites of La_{1 ? c + x} Sr _{c ? x} ²⁺ Mn_{1 ? x} Me _x ²⁺ O_{3 + γ} (Me = Mg, Zn, Ni) systems depending on the concentration of substituting divalent cations (0.15 ≤ c ≤ 0.35; 0.025 ≤ x ≤ 0.100).     

Local environment effect on magnetic states of atoms in transition-metal alloys

The distinction between the localized and the induced magnetic moment on an atom in a ferromagnetic alloy is discussed on the basis of the itinerant-electron theory in the Hartree-Fock approximation. The results of the theoretical calculation on the effect of the nearest neighbour shell are presented for Fe-V and Ni-Fe alloys. Various types of instability of the Fe magnetic moment in Ni-Fe alloys, which are particularly important in the Invar region, are pointed out.     

Quantum states of neutral atoms bound in the magnetic field of a Kepler-guide

The spectrum and the wave function of neutral atoms in the magnetic field of a Kepler-guide are presented by reducing a two-dimensional stationary Schrdinger equation to a one-dimensional hydrogen atom in Rydberg states. In addition, we set the scale for     

Preparation of cluster states of four distant atoms by the interference of polarized photons

We propose a protocol to generate the cluster states of four A-type three-level atoms trapped in distant cavities by using the interference of polarized photons. The protocol uses the effects of the quantum statistics of indistinguishable photons emitted by the atoms inside optical cavities. This makes the protocol more realizable in experiments. The text was submitted by the authors in English.     

Interactions of magnetic monopoles with nuclei and atoms: Formation of bound states and phenomenological consequences

We discuss the binding of magnetic monopoles to nuclear and atomic systems. The energy spectrum is calculated, by assuming an interaction with a hard core. The formation process of monopole-nucleus bound states is analysed and it is shown that monopoles reaching Earth are most likely bound to a proton. We also discuss phenomenological implications of the existence of bound states in connection with the monopole catalysis of proton decay.     

The lattice dynamics of systems with several identical atoms per unit surface cell: a unit cell spectral density

In studies of the lattice dynamics of surfaces in which there are many identical atoms in the unit cell, for example a reconstructed surface, there is a problem in presenting the results. The problem arises because each atom in the unit cell has a different spectral density and it is not, in general, clear which of the many densities should be presented. We propose here that in such studies a “unit cell spectral density”, one which replaces the collection of densities for individual atoms with a single density, should be used. The relationship of this unit cell spectral density to experimental phonon measurements is also discussed.     

Optical evidence of quantum rotor orbital excitations in orthorhombic manganites

In magnetic compounds with Jahn–Teller (JT) ions (such as Mn³⁺ or Cu²⁺), the ordering of the electron or hole orbitals is associated with cooperative lattice distortions. There the role of JT effect, although widely recognized, is still elusive in the ground state properties. Here we discovered that, in these materials, there exist excitations whose energy spectrum is described in terms of the total angular momentum eigenstates and is quantized as in quantum rotors found in JT centers. We observed features originating from these excitations in the optical spectra of a model compound LaMnO₃ using ellipsometry technique. They appear clearly as narrow sidebands accompanying the electron transition between the JT split orbitals at neighboring Mn³⁺ ions, displaying anomalous temperature behavior around the Néel temperature T_N ≈ 140 K. We present these results together with new experimental data on photoluminescence found in LaMnO₃, which lend additional support to the ellipsometry implying the electronic-vibrational origin of the quantum rotor orbital excitations. We note that the discovered orbital excitations of quantum rotors may play an important role in many unusual properties observed in these materials upon doping, such as high-temperature superconductivity and colossal magnetoresistance.     

Spin freezing and magnetic inhomogeneities in bilayer manganites

We have performed a muon spin rotation study on polycrystalline samples of electron-doped layered manganites, La2-2xSr1+2xMn2O7 (0.4< or =x<1), in order to investigate the local magnetic structure and spin dynamics. Our results provide evidence for phase separation into A-type antiferromagnetic and charge-ordered phases for x=0.52 and spin freezing at low temperatures (T<100 K) for 0.52< or =x<0.75. A new phase diagram which includes this spin-freezing region is proposed.     

Characteristics of the phase-separated state in manganites: Relationship with transport and magnetic properties

Journal of Experimental and Theoretical Physics - The temperature and magnetic field dependence of the resistivity, magnetoresistance, and magnetic susceptibility of phase-separated manganites in...     

Optical pumping and population transfer of nuclear-spin states of caesium atoms in high magnetic fields

Nuclear-spin states of gaseous-state Cs atoms in the ground state are optically manipulated using a Ti:sapphire laser in a magnetic field of 1.516T, in which optical coupling of the nuclear-spin states is achieved through hyperfine interactions between electrons and nuclei. The steady-state population distribution in the hyperfine Zeeman sublevels of the ground state is detected by using a tunable diode laser. Furthermore, the state population transfer among the hyperfine Zeeman sublevels, which results from the collision-induced modification \delta a(\bm S \cdot \bm I) of the hyperfine interaction of Cs in the ground state due to stochastic collisions between Cs atoms and buffer-gas molecules, is studied at different buffer-gas pressures. The experimental results show that high-field optical pumping and the small change \delta a(\bm S \cdot \bm I) of the hyperfine interaction can strongly cause the state population transfer and spin-state interchange among the hyperfine Zeeman sublevels. The calculated results maybe explain the steady-state population in hyperfine Zeeman sublevels in terms of rates of optical-pumping, electron-spin flip, nuclear spin flip, and electron-nuclear spin flip-flop transitions among the hyperfine Zeeman sublevels of the ground state of Cs atoms. This method may be applied to the nuclear-spin-based solid-state quantum computation.     

轨道序对半掺杂锰氧化物光学性质的影响

在两轨道双交换模型基础上，讨论了电子关联作用对半掺杂锰氧化物轨道序的影响，推导出能计算各个相的光电导公式.结果显示，光吸收与轨道序之间存在关联现象.对于铁磁相，当格点库仑相互作用(U)从无到有逐渐增加时，铁磁相会从无轨道序过渡到有轨道序，相变前 后非相干光吸收有一个从无能隙到有能隙的明显变化.对于层状反铁磁的A相，U的增加会使 轨道序更明显，非相干光吸收部分的能隙随之也增大. 关键词： 轨道序 光电导 锰氧化物 库仑相互作用     

Dynamics of the charge transferred states relevant to magnetic phase transition in rubidium manganese hexacyanoferrate

Photoinduced charge transfer dynamics in the photomagnetic material RbMn[Fe(CN)₆], which exhibits a magnetic phase transition with a large hysteresis loop (230-300 K), has been investigated by observing the CN⁻ stretching modes, which are sensitive to the valences of the adjacent transition metal ions. Mid-infrared transient absorption measurements were performed between 2013 and 2179 cm⁻¹ to observe the transient and persistent products. The sample in the high-temperature phase was excited by 400 nm laser pulses at the ligand to metal charge transfer band near the high-temperature end of the hysteresis loop. Bleach of the Fe³⁺-CN⁻-Mn²⁺ band representing a decrease of the high-temperature phase and increases of the Fe²⁺-CN⁻-Mn³⁺ and Fe²⁺-CN⁻-Mn²⁺ bands were observed in picosecond time region, indicating a transient production of charge transferred states.     

Efros-Shklovskii law and localized states in weakly doped lanthanum manganites

The existence of clusters in weakly doped lanthanum manganites at temperatures about twice as high as their Curie temperature T _C has been shown. Electrical resistance in weakly doped lanthanum manganites obeys the Efros-Shklovskii law. The temperature and magnetic-field dependences of a cluster size determined from the magnetotransport properties have been described using the model of phase separation into small metallic droplets within the dielectric paramagnetic and antiferromagnetic matrices. The results agree with the existence of the Griffiths phase.     

Cation ordering and magnetic properties of neodymium-barium manganites

Nd_0.70Ba_0.30MnO_3+δ manganites with an ordered arrangement of Nd³⁺ and Ba²⁺ cations are fabricated. The initial stoichiometric Ba-disordered Nd_0.70Ba_0.30MnO₃ solid solution is synthesized in air using a traditional ceramic technology, is characterized by an orthorhombic unit cell (space group Imma, Z = 4), and is ferromagnetic with Curie temperature T _C ≈ 151 K. The average crystallite size in the initial sample is 〈D〉 ≈ 2.169 μm. Annealing of the initial sample in a reducing atmosphere at a pressure P[O₂] ≈ 10^?4 Pa and then in air at T = 800°C leads to the formation of a material with a crystallite size 〈D〉 ≈ 440 nm. This material consists of the following two perovskite phases: a Ba-ordered stoichiometric NdBaMn₂O₆ phase with a tetragonal unit cell (P4/mmm, Z = 2) and a Curie temperature of ～301 K and a Ba-disordered hyperstoichiometric Nd_0.90Ba_0.10MnO_3+δ phase with an orthorhombic unit cell (Imma, Z = 4) and T _C ～ 121 K. Significant changes in the magnetic properties are explained in terms of chemical phase separation with allowance for cation ordering.     

Tunable Wigner states with dipolar atoms and molecules

We study the few-body physics of trapped atoms or molecules with electric or magnetic dipole moments aligned by an external field. Using exact numerical diagonalization appropriate for the strongly correlated regime, as well as a classical analysis, we show how Wigner localization emerges with increasing coupling strength. The Wigner states exhibit nontrivial geometries due to the anisotropy of the interaction. This leads to transitions between different Wigner states as the tilt angle of the dipoles with the confining plane is changed. Intriguingly, while the individual Wigner states are well described by a classical analysis, the transitions between different Wigner states are strongly affected by quantum statistics. This can be understood by considering the interplay between quantum-mechanical and spatial symmetry properties. Finally, we demonstrate that our results are relevant to experimentally realistic systems.