172 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.
Chiral properties of hematite ({\alpha}-Fe2O3) inferred from resonant Bragg diffraction using circularly polarized x-rays
Chiral properties of the two phases - collinear motif (below Morin transition
temperature, TM=250 K) and canted motif (above TM) - of magnetically ordered
hematite ({\alpha}-Fe2O3) have been identified in single crystal resonant x-ray
Bragg diffraction, using circular polarized incident x-rays tuned near the iron
K-edge. Magneto-electric multipoles, including an anapole, fully characterize
the high-temperature canted phase, whereas the low-temperature collinear phase
supports both parity-odd and parity-even multipoles that are time-odd. Orbital
angular momentum accompanies the collinear motif, while it is conspicuously
absent with the canted motif. Intensities have been successfully confronted
with analytic expressions derived from an atomic model fully compliant with
chemical and magnetic structures. Values of Fe atomic multipoles previously
derived from independent experimental data, are shown to be completely
trustworthy
Dramatic role of critical current anisotropy on flux avalanches in MgB2 films
Anisotropic penetration of magnetic flux in MgB2 films grown on vicinal
sapphire substrates is investigated using magneto-optical imaging. Regular
penetration above 10 K proceeds more easily along the substrate surface steps,
anisotropy of the critical current being 6%. At lower temperatures the
penetration occurs via abrupt dendritic avalanches that preferentially
propagate {\em perpendicular} to the surface steps. This inverse anisotropy in
the penetration pattern becomes dramatic very close to 10 K where all flux
avalanches propagate in the strongest-pinning direction. The observed behavior
is fully explained using a thermomagnetic model of the dendritic instability.Comment: 4 pages, 5 figure
Magnetic properties of GdZn (T = Fe, Co) investigated by X-ray diffraction and spectroscopy
We investigate the magnetic and electronic properties of the GdZn
( = Fe and Co) compounds using X-ray resonant magnetic scattering (XRMS),
X-ray absorption near-edge structure (XANES) and X-ray magnetic circular
dichroism (XMCD) techniques. The XRMS measurements reveal that the
GdCoZn compound has a commensurate antiferromagnetic spin structure
with a magnetic propagation vector =
below the N\'eel temperature ( 5.7 K). Only the Gd ions carry a magnetic moment forming an
antiferromagnetic structure with magnetic representation . For the
ferromagnetic GdFeZn compound, an extensive investigation was
performed at low temperature and under magnetic field using XANES and XMCD
techniques. A strong XMCD signal of about 12.5 and 9.7 is observed
below the Curie temperature ( 85 K) at the Gd- and edges,
respectively. In addition, a small magnetic signal of about 0.06 of the
jump is recorded at the Zn -edge suggesting that the Zn 4 states are spin
polarized by the Gd 5 extended orbitals
Orbital ordering transition in CaRuO observed with resonant x-ray diffraction
Resonant x-ray diffraction performed at the and
absorption edges of Ru has been used to investigate the magnetic and orbital
ordering in CaRuO single crystals. A large resonant enhancement due to
electric dipole transitions is observed at the wave-vector
characteristic of antiferromagnetic ordering. Besides the previously known
antiferromagnetic phase transition at K, an additional phase
transition, between two paramagnetic phases, is observed around 260 K. Based on
the polarization and azimuthal angle dependence of the diffraction signal, this
transition can be attributed to orbital ordering of the Ru electrons.
The propagation vector of the orbital order is inconsistent with some
theoretical predictions for the orbital state of CaRuO.Comment: to appear in PR
Pressure-Induced Rotational Symmetry Breaking in URuSi
Phase transitions and symmetry are intimately linked. Melting of ice, for
example, restores translation invariance. The mysterious hidden order (HO)
phase of URuSi has, despite relentless research efforts, kept its
symmetry breaking element intangible. Here we present a high-resolution x-ray
diffraction study of the URuSi crystal structure as a function of
hydrostatic pressure. Below a critical pressure threshold kbar,
no tetragonal lattice symmetry breaking is observed even below the HO
transition K. For , however, a pressure-induced rotational
symmetry breaking is identified with an onset temperatures K.
The emergence of an orthorhombic phase is found and discussed in terms of an
electronic nematic order that appears unrelated to the HO, but with possible
relevance for the pressure-induced antiferromagnetic (AF) phase. Existing
theories describe the HO and AF phases through an adiabatic continuity of a
complex order parameter. Since none of these theories predicts a
pressure-induced nematic order, our finding adds an additional symmetry
breaking element to this long-standing problem.Comment: 6 pages, 4 figures and supplemental material
Magnetic order in GdMnO3 in magnetic fields
Resonant magnetic x ray scattering at the Gd L2 edge is used to investigate the magnetic order of the Gd moments in multiferroic GdMnO3 at low temperatures. We present high magnetic field data on the magnetic ordering of Gd in the ferroelectric phase of GdMnO3. Our findings reaffirm the important role of the Gd moments in the symmetric magnetic exchange striction responsible for ferroelectricity in this compoun
Oxygen superstructures throughout the phase diagram of
Short-range lattice superstructures have been studied with high-energy x-ray
diffuse scattering in underdoped, optimally doped, and overdoped . A new four-unit-cell superstructure was observed in
compounds with . Its temperature, doping, and material dependence
was used to attribute its origin to short-range oxygen vacancy ordering, rather
than electronic instabilities in the layers. No significant diffuse
scattering is observed in YBaCuO. The oxygen superstructures must
be taken into account when interpreting spectral anomalies in
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