Giant magnetotransport phenomena including the field-induced nonmetal-metal transition have been found in single crystals of La 1- x Sr MnO 3 near critical composition ( ≈0.17) for and temperature region around magnetic phase transition. Change resistivity shows a universal curve as function magnitude temperature- or magnetization, most which agrees with prediction by D =∞ S Kondo lattice model strong ferromagnetic (Hund) coupling.

The Kondo lattice Hamiltonian with ferromagnetic Hund's coupling as a model for manganites is investigated. classical limit the spin of (localized) $t_{2g}$ electrons analyzed on lattices dimension 1,2,3 and $\infty$ using several numerical methods. phase diagram at low temperature presented. A regime identified where separation occurs between hole undoped antiferromagnetic hole-rich regions. Experimental consequences this novel are discussed. Regions incommensurate correlations have also...

The Kondo lattice model with Hund's ferromagnetic spin coupling is investigated as a microscopic of the perovskite-type 3 d transitionmetal oxide La 1- x Sr MnO . In classical limit S =∞ and infinite-dimensional D =∞, one-body Green's function exactly calculated. Transport properties system in presence magnetic fields are obtained. giant magnetoresistance this model, which good agreement experimental data , explained by spin-disorder scattering process.

We study the renormalization-group (RG) flow of interactions in two-dimensional ${t\ensuremath{-}t}^{\ensuremath{'}}$ Hubbard model near half-filling an N-patch representation whole Fermi surface. Starting from weak to intermediate couplings flows are strong coupling, with different characters depending on choice parameters. In a large parameter region elastic umklapp scatterings drive instability which parts surface exhibits key signatures insulating spin liquid (ISL), as proposed by...

The phase diagram of the ferromagnetic Kondo model for manganites was recently investigated using computational techniques by Yunoki et al. [Phys. Rev. Lett. 80, 845 (1998)]. In dimensions 1, 2, and $\ensuremath{\infty}$ classical localized spins, this study suggested a rich low-temperature with three dominant regions: (i) phase, (ii) separation between hole-undoped antiferromagnetic hole-rich domains, (iii) incommensurate spin correlations. purpose present paper is twofold: (a) First,...

The Hubbard model on a square lattice in the ground state is investigated. Various aspects of Mott transition at half-filling are clarified from quantum Monte Carlo study. Critical exponents for charge and spin correlations estimated. For doping concentration δ, susceptibility proportional to δ -1 indicating divergence mass δ→0, while always finite not singular near δ=0. Several theoretical consequences above results discussed. Incommensurate peak amplitude correlation scales as (δ-δ c )...

We study a two-dimensional Fermi liquid with surface containing the saddle points $(\ensuremath{\pi},0)$ and $(0,\ensuremath{\pi})$. Including Cooper Peierls channel contributions leads to one-loop renormalization group flow strong coupling for short range repulsive interactions. In certain parameter characteristics of fixed point, opening spin charge gap, dominant pairing correlations are similar those two-leg ladder at half-filling. argue that an increase electron density truncation only...

We have investigated the variation of induced ferroelectric polarization under a magnetic field with various directions and magnitudes in staggered antiferromagnet Ba₂CoGe₂O₇. While cannot be explained by well-accepted spin current model nor exchange striction mechanism, we shown that it is spin-dependent p-d hybridization between transition metal (Co) ligand (O) via spin-orbit interaction. On basis correspondence direction electric state, also demonstrated electrical control magnetization direction.

Orthorhombically distorted perovskite manganites, $R\mathrm{Mn}{\mathrm{O}}_{3}$ with $R$ being a trivalent rare-earth ion, exhibit variety of magnetic and electric phases including multiferroic (i.e., concurrently ferroelectric) fascinating magnetoelectric phenomena. We theoretically study the phase diagram by constructing microscopic spin model, which includes not only superexchange interaction but also single-ion anisotropy (SIA) Dzyaloshinsky-Moriya (DMI). Analysis this model using Monte...

Magnetoelectric phase diagrams of the rare-earth ($R$) Mn perovskites $R$MnO${}_{3}$ are theoretically studied by focusing on crucial roles symmetric magnetostriction or Peierls-type spin-phonon coupling through extending our previous work [M. Mochizuki et al., Phys. Rev. Lett. 105, 037205 (2010)]. We first construct a microscopic classical Heisenberg model for including frustrated spin exchanges, single-ion anisotropy, and Dzyaloshinskii-Moriya interaction. also incorporate lattice degree...

Numerous attempts have been made to realize crossed coupling between ferroelectricity and magnetism in multiferroic materials at room temperature. BiFeO3 is the most extensively studied material that shows multiferroicity temperatures significantly above Here we present high-field experiments on high-quality mono-domain crystals reveal substantial electric polarization orthogonal widely recognized one along trigonal c axis. This novel appears couple with domains of cycloidal spin order and,...

As an effective model to describe perovskite-type manganates (La,A)MnO 3 , the double-exchange on a cubic lattice is investigated.Spin excitation spectrum of in ground state studied using spin wave approximation.Spin dispersion relation observed inelastic neutron scattering experiment La 0.7 Pb 0.3 MnO reproduced.Effective values for electron bandwidth as well Hund's coupling estimated from data.

We report the dielectric dispersion of giant magnetocapacitance (GMC) in multiferroic DyMnO3 over a wide frequency range. The GMC is found to be attributable not softened electromagnon but electric-field-driven motion domain wall (DW). In contrast conventional ferroelectric DWs, present DW holds an extremely high relaxation rate approximately 10;{7} s;{-1} even at low temperatures. This mobile nature as well model simulation suggests that atomically thin ferroelectrics thick, reflecting its...

We investigated the charge-ordered (CO) state in spinel AlV2O4 by electron diffraction, synchrotron x-ray and magnetic measurements. It was found that CO structure appearing below 700 K is characterized formation of V clusters (heptamers), each which consisting 7 vanadium atoms a spin-singlet as total. Theoretical consideration indicates this unique molecularlike heptamer stabilized strong bonding t(2g) orbitals.

We theoretically study origins of the ferroelectricity in multiferroic phases rare-earth (R) Mn perovskites, RMnO3, by constructing a realistic spin model including spin-phonon coupling, which reproduces entire experimental phase diagram plane temperature and Mn-O-Mn bond angle for first time. Surprisingly we reveal significant contribution symmetric (S.S)-type magnetostriction to even spin-spiral-based phase, can be larger than usually expected antisymmetric (SxS)-type contribution. This...

We study theoretically the electromagnon and its optical spectrum (OS) of terahertz-frequency regime in magnetic-spiral-induced multiferroic phases rare-earth (R) Mn perovskites, RMnO3, taking into account elliptical deformation or higher harmonics spiral spin configuration, which has been missed so far. A realistic Hamiltonian, gives phase diagrams agreement with experiments, resolves a long standing puzzle, i.e., double-peak structure OS larger low-energy peak originating from magnon modes...

Effects of disorder on the two competing phases, i.e., ferromagnetic metal and commensurate charge/lattice ordered insulator, are studied by Monte Carlo simulation. The suppresses ordering more strongly than order, driving insulator to near phase boundary in pure case. Above transition temperature, contrary, makes system insulating, which might cause an enhanced colossal magnetoresistance as observed half-doped or Cr-substituted manganites. No indication percolation cluster formation is...

Ferromagnetic transition in three-dimensional double-exchange models is studied by the Monte Carlo method. Critical temperature T c precisely determined finite-size scaling analysis. Strong spin fluctuations this itinerant system significantly reduce from mean-field estimates. By choosing appropriate parameters, obtained values of quantitatively agree with experiments for ferromagnetic metal regime (La,Sr)MnO 3 , which a typical perovskite manganite showing colossal magnetoresistance. This...

Using the Kondo lattice model with classical spins in infinite dimension, conductivity perovskite-type 3 d transition-metal oxide (La, Sr)MnO is theoretically studied. Green's functions as well spontaneous magnetization are obtained exactly on Bethe a function of temperature. Conductivity calculated from Kubo formula. Below Curie temperature, resistivity good agreement experimental data. Anomalous behavior temperature dependence optical observed also explained.

Using the Kondo lattice model with classical spins in infinite dimension, magnetic phase transition perovskite-type $3d$ transition-metal oxide (La,Sr)MnO$_3$ is theoretically studied. On Bethe lattice, self-consistency equations are solved exactly. Curie temperatures at region of double-exchange ferromagnetism $0.1 < x 0.25$ as well Neel temperature $x=0$ reproduced quantitatively. Pressure effect on also discussed.

The wide range optical spectra on a multiferroic prototype ${\mathrm{TbMnO}}_{3}$ have been investigated to clarify the origin of spin excitations observed in far-infrared region. We elucidate full band structure, whose high energy edge ($133\text{ }\text{ }{\mathrm{cm}}^{\ensuremath{-}1}$) exactly corresponds twice highest-lying magnon energy. Thus this absorption is clearly assigned two-magnon excitation driven by electric field light. There an overlap between and phonon ranges, where...

Recent spectroscopic studies at terahertz frequencies for a variety of multiferroics endowed with both ferroelectric and magnetic orders have revealed the possible emergence new collective excitation, frequently referred to as electromagnon. It is in origin, but it becomes active response electric field component light. Here we give an overview our recent advance time-domain spectroscopy electromagnons, or electric-dipole resonances, focused on perovskite manganites—RMnO3 (R denotes...