A. S. Belozerov

Magnetism of iron and nickel from rotationally invariant Hirsch-Fye quantum Monte Carlo calculations

We present a rotationally invariant Hirsch-Fye quantum Monte Carlo algorithm in which the spin rotational invariance of Hund’s exchange is approximated by averaging over all possible directions of the spin quantization axis. We employ this technique to perform benchmark calculations for the two- and three-band Hubbard models on the infinite-dimensional Bethe lattice. Our results agree quantitatively well with those obtained using the continuous-time quantum Monte Carlo method with rotationally invariant Coulomb interaction. The proposed approach is employed to compute the electronic and magnetic properties of paramagnetic α iron and nickel. The obtained Curie temperatures agree well with experiment. Our results indicate that the magnetic transition temperature is significantly overestimated by using the density-density type of Coulomb interaction.

Rotationally invariant exchange interaction: The case of paramagnetic iron

We present a generalization of the spin-fluctuation theory of magnetism which allows us to treat the full rotational invariance of the exchange interaction. The approach is formulated in terms of the local density approximation plus dynamical mean-field theory (

Structural γ–ε phase transition in Fe–Mn alloys from a CPA + DMFT approach

\text{LDA}+\text{DMFT}

Searching for pure iron in nature: the Chelyabinsk meteorite

), providing a systematic many-body treatment of the effect of spin-density fluctuations. This technique is employed to study the electronic and magnetic properties of paramagnetic

Evidence for strong Coulomb correlations in the metallic phase of vanadium dioxide

\ensuremath{\alpha}

Paramagnetic properties of Fe-Mn and Fe-V alloys: a DMFT study.

iron. Our result for the Curie temperature is in good agreement with experiment, while the calculations with the Ising-type exchange interaction yield almost twice the overestimated value.

Preserving spin rotational symmetry in quantum Monte Carlo for description of magnetic properties of strongly correlated compounds

We present a computational scheme for total energy calculations of disordered alloys with strong electronic correlations. It employs the coherent potential approximation combined with the dynamical mean-field theory and allows one to study the structural transformations. The material-specific Hamiltonians in the Wannier function basis are obtained by density functional theory. The proposed computational scheme is applied to study the γ-ε structural transition in paramagnetic Fe-Mn alloys for Mn content from 10 to 20 at.%. The electronic correlations are found to play a crucial role in this transition. The calculated transition temperature decreases with increasing Mn content and is in good agreement with experiment. We demonstrate that in contrast to the α-γ transition in pure iron, the γ-ε transition in Fe-Mn alloys is driven by a combination of kinetic and Coulomb energies. The latter is found to be responsible for the decrease of the γ-ε transition temperature with Mn content.

MonoclinicM1phase of VO2: Mott-Hubbard versus band insulator

Herein we aimed to use thermomagnetic analysis (TMA) to determine the nature of iron and nickel in the Chelyabinsk meteorite, and their effect on the meteorites magnetism. Our magnetic measurements show that 3% of the meteorite is metallic and consists of two ferromagnetic phases with Curie temperatures of TC1 = 1049 K and TC2 = 800 K. Using an Fe–Ni phase diagram, we show that the lower of the two temperatures is due to an Fe–Ni alloy with 51% Ni, while the higher Curie temperature phase is due to a pure or nearly pure (Ni-free) iron phase, for which we can be certain the Ni content is less than 1%. X-ray absorption (XAS) measurements show there are two clearly distinct iron oxidation environments: metallic and 2+, with the 2+ regions differing significantly from the standard FeO phase. We also demonstrate that beneath the immediate surface, iron exists virtually entirely in a metallic state. We are then able to estimate the surface composition using XPS, for which we found that 10% of iron on the surface is still surprisingly unoxidized. Finally, our theoretical calculations show how the density of states for both Fe and Ni atoms is affected for different nickel concentrations.

Specific heat of a binary alloy within the CPA+DMFT method

The influence of Coulomb correlations on magnetic and spectral properties in the metallic rutile phase of vanadium dioxide is studied by state of the art LDA + DMFT method. Calculation results in strongly correlated metallic state with an effective mass renormalization m*/m ≈ 2. Uniform magnetic susceptibility shows Curie-Weiss temperature dependence with effective magnetic moment, pefftheor = 1.54μB, in a good agreement with the experimental value peffexp = 1.53μB that is close to ideal value for V4+ ion with the spin S = 1/2, peff = 1.73μB. Calculated spectral function shows well developed Hubbard bands observable in the recent experimental photoemission spectra. We conclude that VO2 in rutile phase is strongly correlated metal with local magnetic moments formed by vanadium d-electrons.

17 O NMR study of the triangular lattice antiferromagnet CuCrO 2

We calculate magnetic susceptibility of paramagnetic bcc Fe-Mn and Fe-V alloys by two different approaches. The first approach employs the coherent potential approximation (CPA) combined with the dynamical mean-field theory (DMFT). The material-specific Hamiltonians in the Wannier function basis are obtained by density functional theory. In the second approach, we construct supercells modeling the binary alloys and study them using DMFT. Both approaches lead to a qualitative agreement with experimental data. In particular, the decrease of Curie temperature with Mn content and a maximum at about 10 at.% V are well described in units of the Curie temperature of pure iron. In contrast to the Mn impurities, the V ones are found to be antiferromagnetically coupled to Fe atoms. Our calculations for the two-band Anderson-Hubbard model indicate that the antiferromagnetic coupling is responsible for a maximum in the concentration dependence of Curie temperature in Fe-V alloys.