Anatoliy E. Nikiforov

Structure and lattice dynamics of Jahn-Teller crystal BiMnO3: ab initio calculation

In this work, ab initio study of crystal structure and phonon spectra of BiMnO3 has been performed using density functional theory (DFT) with hybrid DFT/Hartree-Fock functionals in CRYSTAL14 code. Crystal structure parameters, infrared and Raman spectra of BiMnO3 have been calculated for magnetic ordered monoclinic C2/c phase. Results are compared with existing experimental data. Our results are in agreement with last x-ray diffraction and optical experiments. Using isotopic substitution method ions involved in vibrations are determined. Calculated charge density maps show the antiferroelectric ordering of dipole moments of Bi3+.

Hyperfine Interactions on Magnetic Ions Nuclei in Titanates

The electric and magnetic hyperfine interaction parameters (υQ, η, Hc) on 47,49Ti nuclei in lanthanum and yttrium titanates were calculated in the cluster model by the unrestricted Hartree-Fock method. The calculation in the cluster approach describes the experimental data better than that in the frameworks of LDA and LDA+U model and modern crystal-field theory.

Effects of Non-Magnetic Doping upon Orbital and Magnetic Structures of Lanthanum Manganite

The theoretical model of the crystal structure of lanthanum manganite doped by non-Jahn-Teller ions is proposed. In order to describe the changes in the crystal structure and orbital state of manganese ions subsystem, we use modified shell model and virtual crystal model. The orbital ordering collapse is explained in terms of dynamical Jahn-Teller effect. The model of superexchange interaction helps to find the values of antiferromagnetic and ferromagnetic exchange parameters for dynamical and static orbital states of interacting ions. The magnetic structure of LaMn1-xGaxO3 is explained and magnetic resonance spectrum is predicted.

Theoretical investigation of NMR spectra in rare-earth manganites

The work is aimed to theoretical investigation of orbital and magnetic structure of manganites. The orbitally-dependent exchange interaction model was used in order to describe the superexchange interaction in all range of RMnO3 (R = La, Pr, Nd, Tb, Dy, Ho) orfhorhombic compounds. The model of nearest-neighbour and next-nearest neighbour exchange was used to describe the magnetic structures of manganites with small rare-earth ion sublattice (R = Dy, Tb, Ho). We investigate different types −A, E, non-collinear - of magnetic structures. The models of NMR spectra calculation of Mn3+ ion in RMnO3 compounds are proposed. The theoretical study of the magnetic structure could distinguish The NMR-spectra of antiferromagnetic (A or E) or strongly non-collinear ordering type.

The Effect of Hydrostatic Pressure on Crystal and Orbital Structures of LaMnO3 and LaMn0.5Ga0.5O3

The crystal structure of manganite under pressure is investigated. The influence of external hydrostatical pressure is studied. The theoretical study of magnetic interactions and NMR spectra under pressure is carried out. The influence of Ga-doping is discussed.

Hyperfine interactions in half-doped and 2/3-doped charge-ordering manganites

The present work is devoted to the theoretical interpretation of nuclear magnetic resonance (NMR) spectra on nonmagnetic lanthanum ion in charge-ordered La0.5Ca0.5MnO3 and La0.33Ca0.67MnO3 compounds. It is shown that the anisotropic hyperfine interaction, which arises due to the polarization of lanthanum’s external p-shells, plays a crucial role in spectrum forming. Our model allows to explain experimental spectra. The work is partially supported by CRDF REC-005.