A. Maljuk

Magnetism, Charge Order, and Giant Magnetoresistance in SrFeO~3~-~d~e~l~t~a Single Crystals

The electronic and magnetic properties of SrFeO(3-delta) single crystals with controlled oxygen content (0< or =delta< or =0.19) have been studied systematically by susceptibility, transport, and spectroscopic techniques. An intimate correlation between the spin-charge ordering and the electronic transport behavior is found. Giant negative as well as positive magnetoresistance are observed.

Single-crystal growth and investigation of NaxCoO2and NaxCoO2.yH2O

A systematic study of NaxCoO2 (x=0.50 - 0.90) and NaxCoO2 yH(D)2O (x=0.26 - 0.42, y=1.3) has been performed to determine phase stability and the effect of hydration on the structural and superconducting properties of this system. We show that a careful control of the Na deintercalation process and hydration dynamics is possible in single crystals of this system. Furthermore, we give experimental evidence that the dependence of the superconducting transition temperature on Na content is much weaker than reported earlier. Implications of this effect for the understanding of the superconducting phase diagram are discussed.

Magnetic structure of the edge-sharing copper oxide chain compound NaCu 2 O 2

Single-crystal neutron diffraction has been used to determine the incommensurate magnetic structure of

Optical response of ferromagnetic Y Ti O 3 studied by spectral ellipsometry

{\text{NaCu}}_{2}{\text{O}}_{2}

Ferromagnetism and lattice distortions in the perovskite YTiO3

, a compound built up of chains of edge-sharing

Phase stability limit of RuSr2GdCu2O8 at various partial oxygen pressures

{\text{CuO}}_{4}

Optical response of ferromagneticYTiO3studied by spectral ellipsometry

plaquettes. Magnetic structures compatible with the lattice symmetry were identified by a group-theoretical analysis and their magnetic structure factors were compared to the experimentally observed Bragg intensities. In conjunction with other experimental data, this analysis yields an elliptical helix structure in which both the helicity and the polarization plane alternate among copper-oxide chains. This magnetic ground state is discussed in the context of the recently reported multiferroic properties of other copper-oxide chain compounds.

The effect of B2O3 addition on La2−xSrxCuO4 single-crystal growth

We have studied the temperature dependence of spectroscopic ellipsometry spectra of an electrically insulating, nearly stoichiometric YTiO_3 single crystal with ferromagnetic Curie temperature T_C = 30 K. The optical response exhibits a weak but noticeable anisotropy. Using a classical dispersion analysis, we identify three low-energy optical bands at 2.0, 2.9, and 3.7 eV. Although the optical conductivity spectra are only weakly temperature dependent below 300 K, we are able to distinguish high- and low-temperature regimes with a distinct crossover point around 100 K. The low-temperature regime in the optical response coincides with the temperature range in which significant deviations from Curie-Weiss mean field behavior are observed in the magnetization. Using an analysis based on a simple superexchange model, the spectral weight rearrangement can be attributed to intersite d_i^1d_j^1 \longrightarrow d_i^2d_j^0 optical transitions. In particular, Kramers-Kronig consistent changes in optical spectra around 2.9 eV can be associated with the high-spin-state (^3T_1) optical transition. This indicates that other mechanisms, such as weakly dipole-allowed p-d transitions and/or exciton-polaron excitations, can contribute significantly to the optical band at 2 eV. The recorded optical spectral weight gain of 2.9 eV optical band is significantly suppressed and anisotropic, which we associate with complex spin-orbit-lattice phenomena near ferromagnetic ordering temperature in YTiO_3.

Magnetic phase diagram of Sr 3 Fe 2 O 7 − δ

The thermodynamic properties of the ferromagnetic perovskite

Magnetic excitations and phonons in the spin-chain compound Na Cu 2 O 2

{\text{YTiO}}_{3}