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Mazurenko V.V.,Ural State Technical University | Shorikov A.O.,RAS Institute of Metal Physics | Lukoyanov A.V.,RAS Institute of Metal Physics | Kharlov K.,Ural State Technical University | And 3 more authors.
Physical Review B - Condensed Matter and Materials Physics | Year: 2010

The LDA+DMFT (local density approximation combined with dynamical mean-field theory) computation scheme has been used to study spectral and magnetic properties of FeSi and Fe1-x Cox Si. Having compared different models, we conclude that a correlated band insulator scenario in contrast to Kondo insulator model agrees well with FeSi band structure and experimental data. Coulomb correlation effects lead to band narrowing of the states near the Fermi level with mass renormalization parameter m *≈.2 in agreement with the results of angle-resolved photoemission spectroscopy. Temperature dependence of spectral functions and magnetic susceptibility calculated in DMFT reproduces transition from nonmagnetic semiconductor to metal with local magnetic moments observed experimentally. Cobalt doping leads to ferromagnetism that has itinerant nature and can be successfully described by the LDA+DMFT method. © 2010 The American Physical Society. Source

Kobler U.,Institute For Festkorperforschung | Hoser A.,Helmholtz Center Berlin
Journal of Magnetism and Magnetic Materials | Year: 2014

The temperature dependence of the magnetic order parameter of NiF 2, MnCO3 and K2NiF4 measured on powder samples is compared with data obtained on single crystals. It is found that the dynamic dimensionality of the NiF2 and MnCO3 powder samples is one-dimensional (1D) for all temperatures T Source

Holder M.G.,TU Dresden | Jesche A.,Max Planck Institute for Chemical Physics of Solids | Lombardo P.,Institute Materiaux | Hayn R.,Institute Materiaux | And 11 more authors.
Physical Review Letters | Year: 2010

As a homologue to the new, Fe-based type of high-temperature superconductors, the electronic structure of the heavy-fermion compound CeFePO was studied by means of angle-resolved resonant photoemission. It was experimentally found-and later on confirmed by local-density approximation (LDA) as well as dynamical mean-field theory (DMFT) calculations-that the Ce 4f states hybridize to the Fe 3d states of d3z2-r2 symmetry near the Fermi level that discloses their participation in the occurring electron-correlation phenomena and provides insight into mechanism of superconductivity in oxopnictides. © 2010 The American Physical Society. Source

Kobler U.,Institute For Festkorperforschung | Hoser A.,Helmholtz Center Berlin
Journal of Magnetism and Magnetic Materials | Year: 2013

The temperature dependence of the order parameter of antiferromagnetic RbMnF 3 has been measured using neutron scattering. After necessary corrections, single crystal data agree perfectly with data obtained on powder material. Surprisingly, the order parameter of cubic RbMnF 3 exhibits the same universal T 5/2 temperature dependence as the order parameter of tetragonal MnF 2. T 5/2 universality class has been identified as characteristic for magnets with one-dimensional continuous dynamic symmetry. It is discussed in some generality that the domain structure is decisive for the dynamic symmetry class. If powder grains are single domain particles one-dimensional behaviour can be anticipated generally. However, bulk single crystals of cubic RbMnF 3 should be in the multi-domain state and should exhibit the T 2 universality class of isotropic magnets with half-integer spin. Isotropy results by a dynamic averaging process over all differently oriented magnetic domains. Since the magneto-elastic coupling of RbMnF 3 is extremely weak it can be assumed that the domain structure is rather coarse. If the domain size is larger than the dynamic length scale of the order parameter the usual averaging process over all domain orientations does not work. Consequently, the observed one-dimensional continuous dynamic symmetry of bulk RbMnF 3 is that of an isolated domain. © 2012 Elsevier B.V. All rights reserved. Source

Betzinger M.,Institute For Festkorperforschung | Friedrich C.,Institute For Festkorperforschung | Blugel S.,Institute For Festkorperforschung | Gorling A.,Friedrich - Alexander - University, Erlangen - Nuremberg
Physical Review B - Condensed Matter and Materials Physics | Year: 2011

We present a general numerical approach to construct local Kohn-Sham potentials from orbital-dependent functionals within the all-electron full-potential linearized augmented-plane-wave (FLAPW) method, in which core and valence electrons are treated on an equal footing. As a practical example, we present a treatment of the orbital-dependent exact-exchange (EXX) energy and potential. A formulation in terms of a mixed product basis, which is constructed from products of LAPW basis functions, enables a solution of the optimized-effective-potential (OEP) equation with standard numerical algebraic tools and without shape approximations for the resulting potential. We find that the mixed product and LAPW basis sets must be properly balanced to obtain smooth and converged EXX potentials without spurious oscillations. The construction and convergence of the exchange potential are analyzed in detail for diamond. Our all-electron results for C, Si, SiC, Ge, and GaAs semiconductors as well as Ne and Ar noble-gas solids are in very favorable agreement with plane-wave pseudopotential calculations. This confirms the adequacy of the pseudopotential approximation in the context of the EXX-OEP formalism and clarifies a previous contradiction between FLAPW and pseudopotential results. © 2011 American Physical Society. Source

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