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We study the critical behavior of a quenched random-exchange Ising model with competing interactions on a bcc lattice. This model was introduced in the study of the magnetic behavior of Fe_{1-x}Ru_x alloys for ruthenium concentrations x=0%,…
In metallic manganites with low Curie temperatures, a peculiar softening of the magnon spectrum close to the magnetic zone boundary has experimentally been observed. Here we present a theory of the renormalization of the magnetic excitation…
Photoirradiation effects in correlated electrons coupled with localized spins are studied based on the extended double-exchange model. In particular, we examine melting of an antiferromagnetic (AFM) charge order insulating state by varying…
Electron-phonon interaction and phonon frequencies of doped polar semiconductors are sensitive to long-range Coulomb forces and can be strongly affected by screening effects of free carriers, the latter changing significantly when…
Unlike the ferropnictide superconductors, which crystallize in a tetragonal crystal structure, binary FeAs forms in an orthorhombic crystal structure, where the local atomic environment resembles a highly distorted variant of the FeAs4…
A double exchange model for degenerate $e_g$ orbitals with intra- and inter-orbital interactions has been studied for the electron doped manganites A$_{1-x}$B$_{x}$MnO$_3$ ($x > 0.5$). We show that such a model reproduces the observed phase…
The double-exchange model, which has been extensively studied in the context of colossal magneto-resistance in perovskite manganese oxides, is known to exhibit a ferromagnetic metallic state at low temperatures because of the interplay…
The paramagnetic insulator to ferromagnetic metal transition in Lanthanum manganites and the associated magnetoresistive phenomena is treated by considering the localization due to random hopping induced by slowly fluctuating spin…
Studying the nature and consequences of electron-phonon interaction in manganites is an area of intense ongoing research. Here, in an attempt to model charge and orbital ordering in manganites displaying C-type antiferromaganetism, we study…
We study the competition of magneto-dipole, anisotropy and exchange interactions in composite three dimensional multiferroics. Using Monte Carlo simulations we show that magneto-dipole interaction does not suppress the ferromagnetic state…
The double exchange model describing the coupling between conduction electrons and localized magnetic moments is relevant for a large family of physical systems including manganites. Here we reveal that the one dimensional double exchange…
Experimental results on the metal-insulator transition and related phenomena in strongly interacting two-dimensional electron systems are discussed. Special attention is given to recent results for the strongly enhanced spin susceptibility,…
Understanding magnetism in multiple magnetic sublattice system, driven by the interplay of varied nature of magnetic exchanges, is on one hand challenging and on other hand intriguing. Motivated by the recent synthesis of AA'BB'O_6 double…
To understand effects of orbital degeneracy on magnetism, in particular effects of Hund's rule coupling, we study the two-orbital Hubbard model on a square lattice by a variational Monte Carlo method. As a variational wave function, we…
A novel ferromagnetic transition, accompanied by carrier density collapse, is found in doped charge-transfer insulators with strong electron-phonon coupling. The transition is driven by an exchange interaction of polaronic carriers with…
A field-theoretical description of the behavior of homogeneous, elastically isotropic, compressible systems characterized by two order parameters at the bicritical and tetracritical points is presented. For three-dimensional Ising-like…
Competition between the ferromagnetic double-exchange interaction and the super-exchange antiferromagnetic interaction is theoretically studied in the presence of geometrical frustration. As increasing the super-exchange interaction, the…
We consider the effect of electron-phonon coupling in semimetals in high magnetic fields, with regard to elastic modes that can lead to a redistribution of carriers between pockets. We show that in a clean three dimensional system, at each…
This paper is a brief review of our recent studies concerning on magnetism and electronic states of lattice systems with Hund coupling. First we examined the effectiveness of the Hund coupling in realizing ferromagnetism in the doubly…
In extensive Monte Carlo simulations the phase transition of the random field Ising model in three dimensions is investigated. The values of the critical exponents are determined via finite size scaling. For a Gaussian distribution of the…