26 research outputs found
Spin-charge-lattice coupling near the metal-insulator transition in Ca3Ru2O7
We report x-ray scattering studies of the c-axis lattice parameter in
Ca3Ru2O7 as a function of temperature and magnetic field. These structural
studies complement published transport and magnetization data, and therefore
elucidate the spin-charge-lattice coupling near the metal-insulator transition.
Strong anisotropy of the structural change for field applied along orthogonal
in-plane directions is observed. Competition between a spin-polarized phase
that does not couple to the lattice, and an antiferromagnetic metallic phase,
which does, gives rise to rich behavior for B b.Comment: 6 pages, 4 figures, to appear in Phys. Rev.
Electronic structure, magnetic and dielectric properties of the edge-sharing copper-oxide chain compound NaCuO
We report an experimental study of \nco, a Mott insulator containing chains
of edge-sharing CuO plaquettes, by polarized x-ray absorption spectroscopy
(XAS), resonant magnetic x-ray scattering (RMXS), magnetic susceptibility, and
pyroelectric current measurements. The XAS data show that the valence holes
reside exclusively on the Cu sites within the copper-oxide spin chains
and populate a -orbital polarized within the CuO plaquettes. The RMXS
measurements confirm the presence of incommensurate magnetic order below a
N\'eel temperature of K, which was previously inferred from
neutron powder diffraction and nuclear magnetic resonance data. In conjunction
with the magnetic susceptibility and XAS data, they also demonstrate a new
"orbital" selection rule for RMXS that is of general relevance for magnetic
structure determinations by this technique. Dielectric property measurements
reveal the absence of significant ferroelectric polarization below , which
is in striking contrast to corresponding observations on the isostructural
compound \lco. The results are discussed in the context of current theories of
multiferroicity.Comment: 7 pages, 7 figure
Magnetic field induced transitions in multiferroic TbMnO3 probed by resonant and non-resonant X-ray diffraction
Multiferroic TbMnO3 is investigated using x-ray diffraction in high magnetic
fields. Measurements on first and second harmonic structural reflections due to
modulations induced by the Mn and Tb magnetic order are presented as function
of temperature and field oriented along the a and b-directions of the crystal.
The relation to changes in ordering of the rare earth moments in applied field
is discussed. Observations below T_N(Tb) without and with applied magnetic
field point to a strong interaction of the rare earth order, the Mn moments and
the lattice. Also, the incommensurate to commensurate transition of the wave
vector at the critical fields is discussed with respect to the Tb and Mn
magnetic order and a phase diagram on basis of these observations for magnetic
fields H||a and H||b is presented. The observations point to a complicated and
delicate magneto-elastic interaction as function of temperature and field.Comment: 12 pages, 15 figures, 2 references adde
Mott versus Slater-type metal-insulator transition in Mn-substituted Sr3Ru2O7
We present a temperature-dependent x-ray absorption (XAS) and resonant
elastic x-ray scattering (REXS) study of the metal-insulator transition (MIT)
in Sr3(Ru1-xMnx)2O7. The XAS results reveal that the MIT drives the onset of
local antiferromagnetic correlations around the Mn impurities, a precursor of
the long-range antiferromagnetism detected by REXS at T_order<T_MIT. This
establishes that the MIT is of the Mott-type (electronic correlations) as
opposed to Slater-type (magnetic order). While this behavior is induced by Mn
impurities, the (1/4,1/4,0) order exists for a wide range of Mn concentrations,
and points to an inherent instability of the parent compound.Comment: In press. A high-resolution version can be found at
http://www.phas.ubc.ca/~quantmat/ARPES/PUBLICATIONS/Articles/MnSRO_REXS.pd
Electronic superlattice revealed by resonant scattering from random impurities in Sr3Ru2O7
Resonant elastic x-ray scattering (REXS) is an exquisite element-sensitive
tool for the study of subtle charge, orbital, and spin superlattice orders
driven by the valence electrons, which therefore escape detection in
conventional x-ray diffraction (XRD). Although the power of REXS has been
demonstrated by numerous studies of complex oxides performed in the soft x-ray
regime, the cross section and photon wavelength of the material-specific
elemental absorption edges ultimately set the limit to the smallest
superlattice amplitude and periodicity one can probe. Here we show -- with
simulations and REXS on Mn-substituted SrRuO -- that these
limitations can be overcome by performing resonant scattering experiments at
the absorption edge of a suitably-chosen, dilute impurity. This establishes
that -- in analogy with impurity-based methods used in electron-spin-resonance,
nuclear-magnetic resonance, and M\"ossbauer spectroscopy -- randomly
distributed impurities can serve as a non-invasive, but now momentum-dependent
probe, greatly extending the applicability of resonant x-ray scattering
techniques
Unrestricted Hartree-Fock Analysis of SrCaRuO
We investigated the electronic and magnetic structure of
SrCaRuO () on the basis of the
double-layered three-dimensional multiband Hubbard model with spin-orbit
interaction. In our model, lattice distortion is implemented as the modulation
of transfer integrals or a crystal field. The most stable states are estimated
within the unrestricted Hartree-Fock approximation, in which the colinear spin
configurations with five different spin-quantization axes are adopted as
candidates. The obtained spin structures for some particular lattice
distortions are consistent with the neutron diffraction results for
CaRuO. Also, some magnetic phase transitions can occur due to
changes in lattice distortion. These results facilitate the comprehensive
understanding of the phase diagram of SrCaRuO.Comment: 16 pages, 7 figure