65 research outputs found
The nature of the charge density waves in under-doped YBaCuO revealed by X-ray measurements of the ionic displacements
All underdoped high-temperature cuprate superconductors appear to exhibit
charge density wave (CDW) order, but both the underlying symmetry breaking and
the origin of the CDW remain unclear. We use X-ray diffraction to determine the
microscopic structure of the CDW in an archetypical cuprate
YBaCuO at its superconducting transition temperature Tc ~ 60
K. We find that the CDWs present in this material break the mirror symmetry of
the CuO2 bilayers. The ionic displacements in a CDW have two components: one
perpendicular to the CuO planes, and another parallel to these planes,
which is out of phase with the first. The largest displacements are those of
the planar oxygen atoms and are perpendicular to the CuO planes. Our
results allow many electronic properties of the underdoped cuprates to be
understood. For instance, the CDW will lead to local variations in the doping
(or electronic structure) giving an explicit explanation of the appearance of
density-wave states with broken symmetry in scanning tunnelling microscopy
(STM) and soft X-ray measurements
Profile of the U 5f magnetization in U/Fe multilayers
Recent calculations, concerning the magnetism of uranium in the U/Fe
multilayer system have described the spatial dependence of the 5f polarization
that might be expected. We have used the x-ray resonant magnetic reflectivity
technique to obtain the profile of the induced uranium magnetic moment for
selected U/Fe multilayer samples. This study extends the use of x-ray magnetic
scattering for induced moment systems to the 5f actinide metals. The spatial
dependence of the U magnetization shows that the predominant fraction of the
polarization is present at the interfacial boundaries, decaying rapidly towards
the center of the uranium layer, in good agreement with predictions.Comment: 7 pages, 6 figure
Simultaneous dynamic electrical and structural measurements of functional materials
A new materials characterization system developed at the XMaS beamline, located at the European Synchrotron Radiation Facility in France, is presented. We show that this new capability allows to measure the atomic structural evolution (crystallography) of piezoelectric materials whilst simultaneously measuring the overall strain characteristics and electrical response to dynamically (ac) applied external stimuli
Temperature dependence of the spin and orbital magnetization density in around the spin-orbital compensation point
Non-resonant ferromagnetic x-ray diffraction has been used to separate the
spin and orbital contribution to the magnetization density of the proposed
zero-moment ferromagnet . The alignment of the
spin and orbital moments relative to the net magnetization shows a sign
reversal at 84K, the compensation temperature. Below this temperature the
orbital moment is larger than the spin moment, and vice versa above it. This
result implies that the compensation mechanism is driven by the different
temperature dependencies of the spin and orbital moments. Specific heat
data indicate that the system remains ferromagnetically ordered throughout
Magnetic field induced effects on the electric polarization in RMnO3 R Dy,Gd
X-ray resonant magnetic scattering studies of rare earth magnetic ordering
were performed on perovskite manganites RMnO3 (R = Dy, Gd) in an applied
magnetic field. The data reveal that the field-induced three-fold polarization
enhancement for H || a (H approx. 20 kOe) observed in DyMnO3 below 6.5 K is due
to a re-emergence of the Mn-induced Dy spin order with propagation vector k(Dy)
= k(Mn) = 0.385 b*, which accompanies the suppression of the independent Dy
magnetic ordering, k(Dy) = 1/2 b*. For GdMnO3, the Mn-induced ordering of Gd
spins is used to track the Mn-ordering propagation vector. The data confirm the
incommensurate ordering reported previously, with k(Mn) varying from 0.245 to
0.16 b* on cooling from T_N(Mn) down to a transition temperature T'. New
superstructure reflections which appear below T' suggest a propagation vector
k(Mn) = 1/4 b* in zero magnetic field, which may coexist with the previously
reported A-type ordering of Mn. The Gd spins order with the same propagation
vector below 7 K. Within the ordered state of Gd at T = 1.8 K we find a phase
boundary for an applied magnetic field H || b, H = 10 kOe, which coincides with
the previously reported transition between the ground state paraelectric and
the ferroelectric phase of GdMnO3. Our results suggest that the magnetic
ordering of Gd in magnetic field may stabilize a cycloidal ordering of Mn that,
in turn, produces ferroelectricity.Comment: 8 Figures, v2: improved figure layou
Antiferromagnetic order and domains in Sr3Ir2O7 probed by x-ray resonant scattering
This article reports a detailed x-ray resonant scattering study of the
bilayer iridate compound, Sr3Ir2O7, at the Ir L2 and L3 edges. Resonant
scattering at the Ir L3 edge has been used to determine that Sr3Ir2O7 is a
long-range ordered antiferromagnet below TN 230K with an ordering wavevector,
q=(1/2,1/2,0). The energy resonance at the L3 edge was found to be a factor of
~30 times larger than that at the L2. This remarkable effect has been seen in
the single layer compound Sr2IrO4 and has been linked to the observation of a
Jeff=1/2 spin-orbit insulator. Our result shows that despite the modified
electronic structure of the bilayer compound, caused by the larger bandwidth,
the effect of strong spin-orbit coupling on the resonant magnetic scattering
persists. Using the programme SARAh, we have determined that the magnetic order
consists of two domains with propagation vectors k1=(1/2,1/2,0) and
k2=(1/2,-1/2,0), respectively. A raster measurement of a focussed x-ray beam
across the surface of the sample yielded images of domains of the order of 100
microns size, with odd and even L components, respectively. Fully relativistic,
monoelectronic calculations (FDMNES), using the Green's function technique for
a muffin-tin potential have been employed to calculate the relative intensities
of the L2,3 edge resonances, comparing the effects of including spin-orbit
coupling and the Hubbard, U, term. A large L3 to L2 edge intensity ratio (~5)
was found for calculations including spin-orbit coupling. Adding the Hubbard,
U, term resulted in changes to the intensity ratio <5%.Comment: 9 pages, 9 figure
Non-uniform Gd distribution and magnetization profiles within GdCoFe alloy thin films
Rare earth (RE):transition metal (TM) ferrimagnetic alloys continue to attract significant attention for spintronics. This work focuses on the elemental distribution of RE and TM elements throughout the thickness of nominally uniform films and the resulting spatial variations of the magnetization within these layers. Samples of CoFe alloyed with Gd were studied using secondary ion mass spectroscopy, polarized neutron reflectometry, and x-ray resonant magnetic reflectivity. The samples were grown by magnetron co-sputtering to control the RE:TM alloy ratio of the ferrimagnetic layer, which was combined with W and Pt layers as either under or over-layers to create sample structures such as W/Gdx(Co70Fe30)100-x/Pt, wherex x=0,8, and 23 at. %. Results show that uniformly deposited thin-films have a significant variation in the distribution of the TM and RE through the film thickness, and this leads to a spatial distribution in the net magnetization profile and a non-uniform Gd magnetization profile within the layer. These findings have implications for the application RE:TM alloys in spintronics as they may impact the perpendicular magnetic anisotropy, the ferrimagnetic compensation temperature, and interfacial spin transport
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