Raman scattering study of anomalous spin, charge, and lattice dynamics in the charge-ordered phase of Bi1-xCaxMnO3 (x > 0.5)

We report an inelastic light scattering study of the effects of charge ordering on the spin, charge, and lattice dynamics of Bi1-xCaxMnO3 (x>0.5). We find that charge ordering results in anomalous phonon behavior, such as the appearance of "activated" modes. More significantly, however, the transition to the charge-ordered phase results in the appearance of a quasielastic scattering response with the symmetry of the spin-chirality operator ( T(1g)); this scattering response is thus indicative of magnetic or chiral spin fluctuations in the antiferromagnetic charge-ordered phase.     

Ab initio evaluation of the charge ordering in alpha'NaV2O5

We report ab initio calculations of the charge ordering in alpha'NaV2O5 using large configurations interaction methods on embedded fragments. Our major result is that the 2p(y) electrons of the bridging oxygen of the rungs present a very strong magnetic character and should thus be explicitly considered in any relevant effective model. The most striking consequence of this result is that the spin and charge ordering differ substantially, as differ the experimental results depending on whether they are sensitive to the spin or charge density.     

Spin, charge, and orbital orderings in iron-based superconductors

In this article, we briefly review spin, charge, and orbital orderings in iron-based superconductors, as well as the multi-orbital models. The interplay of spin, charge, and orbital orderings is a key to understand the high temperature superconductivity. As an illustration, we use the two-orbital model to show the spin and charge orderings in iron-based superconductors based on the mean-field approximation in real space. The typical spin and charge orderings are shown by choosing appropriate parameters, which are in good agreement with experiments. We also show the effect of Fe vacancies, which can introduce the nematic phase and interesting magnetic ground states. The orbital ordering is also discussed in iron-based superconductors. It is found that disorder may play a role to produce the superconductivity.     

Spin current through a tunnel junction

We derive an expression for the spin current through a tunnel barrier in terms of many-body Green’s functions. The spin current has two possible contributions. One is associated with angular momentum transfer due to spin-polarized charge current crossing the junction. If there are magnetic moments on both sides of the tunnel junction, due to spin accumulation or ferromagnetic ordering, then there is a second contribution related to the exchange coupling between the moments.     

New type of charge and magnetic order in the ferromagnetic kondo lattice

We study numerically the one dimensional ferromagnetic Kondo lattice, a model widely used to describe nickel and manganese perovskites. By including a nearest-neighbor Coulomb interaction ( V) and a superexchange interaction between the localized moments ( K), we obtain the phase diagram in parameter space for several dopings at T = 0. Because of the competition between double and superexchange, we find a region where the formation of magnetic polarons induces a charge-ordered state which survives also for V = 0. This mechanism should be taken into account in theories of charge ordering involving spin degrees of freedom.     

Pressure-tuned spin and charge ordering in an itinerant antiferromagnet

Elemental chromium orders antiferromagnetically near room temperature, but the ordering temperature can be driven to zero by applying large pressures. We combine diamond anvil cell and synchrotron x-ray diffraction techniques to measure directly the spin and charge order in the pure metal at the approach to its quantum critical point. Both spin and charge order are suppressed exponentially with pressure, well beyond the region where disorder cuts off such a simple evolution, and they maintain a harmonic scaling relationship over decades in scattering intensity. By comparing the development of the order parameter with that of the magnetic wave vector, it is possible to ascribe the destruction of antiferromagnetism to the growth in electron kinetic energy relative to the underlying magnetic exchange interaction.     

Experimental evidence of coupling interaction between charge ordering and spin ordering

In order to experimentally probe into the complicated interaction between charge ordering and spin ordering in manganites,two sets of samples Nd0.5Sr0.5Mn1-xGaxO3(NSMGO) and Nd 0.5Sr0.5Mn1-y CryO3(NSMCO)(0.0 x,y 0.075),have been studied by means of electrical transport,magnetization,electron spin resonance and transmission electron microscopy analysis.By comparing the influence of Cr-doping and Ga-doping in the Nd0.5Sr0.5MnO3(NSMO) system,large difference between the evolution of charge ordering temperature T co in the Cr-doping and the Ga-doping cases is found.In the NSMCO system,the CE-type antiferromagnetic(AFM)/charge ordering(CO) phase disappears with only 2.5 percent Cr doping;but in the NSMGO system,the CE-type AFM/CO phase always exists.This phenomenon indicates that the charge ordering formation is dominated by the spin ordering.As a result,it is experimentally proved that there is strong coupling interaction between charge ordering and spin ordering in NSMO system.     

Correlation effects in quantum spin-Hall insulators: a quantum Monte Carlo study

We consider the Kane-Mele model supplemented by a Hubbard U term. The phase diagram is mapped out using projective auxiliary field quantum Monte Carlo simulations. The quantum spin liquid of the Hubbard model is robust against weak spin-orbit interaction, and is not adiabatically connected to the spin-Hall insulating state. Beyond a critical value of U>U(c) both states are unstable toward magnetic ordering. In the quantum spin-Hall state we study the spin, charge, and single-particle dynamics of the helical Luttinger liquid by retaining the Hubbard interaction only on a ribbon edge. The Hubbard interaction greatly suppresses charge currents along the edge and promotes edge magnetism but leaves the single-particle signatures of the helical liquid intact.     

Tuning the magnetic dimensionality by charge ordering in the molecular TMTTF salts

We theoretically investigate the interplay between charge ordering and magnetic states in quasi-one-dimensional molecular conductors TMTTF(2)X, motivated by the observation of a complex variation of competing and/or coexisting phases. We show that the ferroelectric-type charge order increases two-dimensional antiferromagnetic spin correlation, whereas in the one-dimensional regime two different spin-Peierls states are stabilized. By using first-principles band calculations for the estimation for the transfer integrals and comparing our results with the experiments, we identify the controlling parameters in the experimental phase diagram to be not only the interchain transfer integrals but also the amplitude of the charge order.     

Coherent magnetic oscillation in the spin ladder system alpha(')- NaV2O5

We report the first observation of coherent magnetic excitations in a spin ladder system NaV2O5 by using femtosecond time-domain spectroscopy. A pronounced coherent oscillation is observed at 127 cm(-1) (nearly twice the spin gap energy) and assigned to a two-magnon bound state, based on the temperature dependence of the intensity below the charge ordering phase transition at T(C) = 34 K. This mode can be observable only when circularly polarized light is used as a pump or a probe beam, suggesting that it corresponds to a spin-flip excitation from the singlet ground state. A phonon mode strongly coupled to the spin state is also found at 303 cm(-1).     

Low to high spin-state transition induced by charge ordering in antiferromagnetic YBaCo2O5

The oxygen-deficient double perovskite YBaCo2O5, containing corner-linked CoO5 square pyramids as principal building units, undergoes a paramagnetic to antiferromagnetic spin ordering at 330 K. This is accompanied by a tetragonal to orthorhombic distortion. Below 220 K orbital ordering and long-range Co(2+)/Co(3+) charge ordering occur as well as a change in the Co2+ spin state from low to high spin. This transition is shown to be very sensitive to the oxygen content of the sample. To our knowledge this is the first observation of a spin-state transition induced by long-range orbital and charge ordering.     

Ferromagnetism and colossal magnetoresistance from phase competition

We report a multicomponent theory for the coexistence of charge ordering (CO), and antiferromagnetic (AFM) and ferromagnetic (FM) spin ordering. This kind of state is invoked for manganites by Moreo et al., Science 283, 2034 (1999) and observed in recent experiments. We show that doping an AFM or CO state always generates a FM component. FM, AFM, and CO necessarily coexist in a particle-hole asymmetric system. Melting of large AFM-CO orders by small magnetic fields and colossal magnetoresistance (CMR) arise whenever the CO and AFM order parameters have similar magnitude and momentum structure. Hole doping favors FM metallic states while electron doping favors AFM-CO states, as in CMR manganites.     

Spin and charge ordering in three-leg ladders in oxyborates

We study the spin ordering within the three-leg ladders present in the oxyborate Fe3O2BO3 consisting of localized classical spins interacting with conduction electrons (one electron per rung). We also consider the competition with antiferromagnetic superexchange interactions to determine the magnetic phase diagram. Besides a ferromagnetic phase we find (i) a phase with ferromagnetic rungs ordered antiferromagnetically and (ii) a zigzag canted spin ordering along the legs. We also determine the induced charge ordering within the different phases and the interplay with lattice instability. Our model is discussed in connection with the lattice dimerization transition observed in this system, emphasizing the role of the magnetic structure.     

Effects of spin ordering on phonon and plasmon spectra,and dielectric properties in magnetic semiconductors

Effects of spin ordering on the phonons, plasmons, and dielectric properties have been investigated for many magnetic crystals, such as Cr-spinels, EuX (X = O, S, Se, Te), and fluorite-type compounds. Of these phenomena, the static dielectric constant and Raman scattering have been extensively discussed. However, the dielectric parameters obtained from infrared spectra have not been discussed in spite of observed various phenomena arising from the direct coupling of spin system with phonons or electrons. Furthermore, these microscopic phenomena can be combined with the macroscopic dielectric values with respect to the spin ordering effect. It will ascertain the mechanism of the spin ordering effect on the values. From this point of view, we review the spin-dependent phenomena on the frequencies of TO and LO phonon modes, phonon damping, optical and static dielectric constants, effective charge, and also on plasmon parameters in the spinel type magnetic semiconductors.     

Instability of the quantum-critical point of itinerant ferromagnets

We study the stability of the quantum-critical point for itinerant ferromagnets commonly described by the Hertz-Millis-Moriya (HMM) theory. We argue that in D相似文献   

Helicoidal ordering in iron perovskites

We study the double exchange in transition metal oxides with itinerant and localized electrons. We show that the charge transfer energy Delta and the oxygen-oxygen hopping amplitude t(pp) have a strong effect on magnetic ordering: while for Delta>0 the ground state is ferromagnetic, for negative Delta and large t(pp) the double exchange gives rise to an incommensurate helicoidal ordering of local spins, observed, e.g., in the iron perovskites SrFeO3 and CaFeO3. For negative Delta, the metal-insulator transition into a charge-ordered state has little effect on magnetic ordering. This explains the difference in magnetic and transport properties of ferrates and manganites.     

Spin gradient demagnetization cooling of ultracold atoms

We demonstrate a new cooling method in which a time-varying magnetic field gradient is applied to an ultracold spin mixture. This enables preparation of isolated spin distributions at positive and negative effective spin temperatures of ±50 pK. The spin system can also be used to cool other degrees of freedom, and we have used this coupling to cool an apparently equilibrated Mott insulator of rubidium atoms to 350?pK. These are the lowest temperatures ever measured in any system. The entropy of the spin mixture is in the regime where magnetic ordering is expected.     

Tailor-made electronic and magnetic properties in one-dimensional pure and Y-substituted Ca3Co2O6

Full-potential density-functional calculations show that the electronic structure of one-dimensional ferrimagnetic Ca3Co2O6 varies from metal to half metal to insulator as its magnetic ordering changes from the ferrimagnetic through the ferromagnetic to the paramagnetic state. The present Letter is the first to establish the occurrence of half metallicity in one-dimensional oxides. Moreover, the electronic and magnetic properties of this material can be tuned by substitution of Y for Ca, as shown by our detailed study on Ca(3-x)YxCo2O6 (x = 0, 0.3, 0.75, and 1). The Co ions are in two different valence states [Co4+ (low-spin) and Co2+ (high-spin)], and hence the occurrence of charge ordering in addition to spin ordering is established. For specific Y concentrations we predict a rarely seen combination of ferromagnetic and insulating behavior.     

The first principle study on the electronic structure and spin ordering of the rare earth palladium sulfide, EuPd3S4

We have performed relativistic first-principles full-potential linearized augmented plane wave (FLAPW) calculation for rare earth palladium sulfide EuPd₃S₄ in the ferromagnetic and antiferromagnetic states. The density of 4f electrons of Eu is taken from a local-spin-density approximation self-interaction correction (LSDA-SIC) atomic calculation. EuPd₃S₄ is found to exhibit antiferromagnetic ordering in its ground state. The charge, orbital, magnetic moment and spin ordering are explained with the electronic structure, the orbital-projected density of states and the total energy study. EuPd₃S₄ is found to be stable in the body-centered Type-I antiferromagnetic state, in agreement with experimental results. Different Eu states are found in antiferromagnetic ordering. The magnetic moments of different states obtained through spin-polarized calculation are also in good agreement with experimental results. The phenomena observed are explained by the orbital hybridization of Eu and Pd ions as compared with the free ions.     

Characterizing a high spin magnetic impurity via Andreev reflection spectroscopy

The ground state properties of a high spin magnetic impurity and its interaction with an electronic spin are probed via Andreev reflection. We see that through the charge and spin conductance one can effectively estimate the interaction strength, the ground state spin and magnetic moment of any high spin magnetic impurity. We show how a high spin magnetic impurity at the junction between a normal metal and superconductor can contribute to superconducting spintronics applications. Particularly, while spin conductance is absent below the gap for Ferromagnet-Insulator-Superconductor junctions we show that in the case of a Normal metal-High spin magnetic impurity-Normal Metal-Insulator-Superconductor (NMNIS) junction it is present. Further, it is seen that pure spin conduction can exist without any accompanying charge conduction in the NMNIS junction.