250 research outputs found
Evidence for charge orbital and spin stripe order in an overdoped manganite
We present diffraction data on a single-layered manganite
La(0.42)Sr(1.58)MnO4 with hole doping (x>0.5). Overdoped La(0.42)Sr(1.58)MnO4
exhibits a complex ordering of charges, orbitals and spins. Single crystal
neutron diffraction experiments reveal three incommensurate and one
commensurate order parameters to be tightly coupled. The position and the shape
of the distinct superstructure scattering points to a stripe arrangement in
which ferromagnetic zigzag chains are disrupted by additional Mn4+ stripes
Evidence for Multiple Phase Transitions in La_1-xCa_xCoO_3
We report thermal-expansion and specific-heat data of the series
La_1-xCa_xCoO_3 for 0 <= x <= 0.3. For x = 0 the thermal-expansion coefficient
alpha(T) features a pronounced maximum around T = 50 K caused by a
temperature-dependent spin-state transition from a low-spin state (S=0) at low
temperatures towards a higher spin state of the Co^3+ ions. The partial
substitution of the La^3+ ions by divalent Ca^2+ ions causes drastic changes in
the macroscopic properties of LaCoO_3. Around x ~ 0.125 the large maximum in
alpha(T) has completely vanished. With further increasing x three different
anomalies develop
Electric-dipole active two-magnon excitation in {\textit{ab}} spiral spin phase of a ferroelectric magnet GdTbMnO
A broad continuum-like spin excitation (1--10 meV) with a peak structure
around 2.4 meV has been observed in the ferroelectric spiral spin phase of
GdTbMnO by using terahertz (THz) time-domain spectroscopy.
Based on a complete set of light-polarization measurements, we identify the
spin excitation active for the light vector only along the a-axis, which
grows in intensity with lowering temperature even from above the magnetic
ordering temperature but disappears upon the transition to the -type
antiferromagnetic phase. Such an electric-dipole active spin excitation as
observed at THz frequencies can be ascribed to the two-magnon excitation in
terms of the unique polarization selection rule in a variety of the
magnetically ordered phases.Comment: 11 pages including 3 figure
Crystal and magnetic structure of La_{1-x}Sr_{1+x}MnO_{4} : role of the orbital degree of freedom
The crystal and magnetic structure of La_{1-x}Sr_{1+x}MnO_4 (0<x<0.7) has
been studied by diffraction techniques and high resolution capacitance
dilatometry. There is no evidence for a structural phase transition like those
found in isostructural cuprates or nickelates, but there are significant
structural changes induced by the variation of temperature and doping which we
attribute to a rearrangement of the orbital occupation.Comment: 8 pages, 6 figures, submitted to PR
Thermal conductivity of R2CuO4, with R = La, Pr and Gd
We present measurements of the in-plane kappa_ab and out-of-plane kappa_c
thermal conductivity of Pr2CuO4 and Gd2CuO4 single crystals. The anisotropy
gives strong evidence for a large contribution of magnetic excitations to
kappa_ab i.e. for a heat current within the CuO2 planes. However, the absolute
values of kappa_mag are lower than previous results on La2CuO4. These
differences probably arise from deviations from the nominal oxygen
stoichiometry. This has a drastic influence on kappa_mag, which is shown by an
investigation of a La2CuO4+delta polycrystal.Comment: 2 pages, 1 figure; presented at SCES200
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