151 research outputs found
Disentangling instrumental broadening
A new procedure aiming at disentangling the instrumental profile broadening
and the relevant X-ray powder diffraction (XRPD) profile shape is presented.
The technique consists of three steps: denoising by means of wavelet
transforms, background suppression by morphological functions and deblurring by
a Lucy--Richardson damped deconvolution algorithm. Real XRPD intensity profiles
of ceria samples are used to test the performances. Results show the robustness
of the method and its capability of efficiently disentangling the instrumental
broadening affecting the measurement of the intrinsic physical line profile.
These features make the whole procedure an interesting and user-friendly tool
for the pre-processing of XRPD data.Comment: 9 pages, 1 table, 1 figure; typos correcte
Evolution of magnetic states in frustrated diamond lattice antiferromagnetic Co(Al1-xCox)2O4 spinels
Using neutron powder diffraction and Monte-Carlo simulations we show that a
spin-liquid regime emerges at $all compositions in the diamond-lattice
antiferromagnets Co(Al1-xCox)2O4. This spin-liquid regime induced by
frustration due to the second-neighbour exchange coupling J2, is gradually
superseded by antiferromagnetic collinear long-range order (k=0) at low
temperatures. Upon substitution of Al3+ by Co3+ in the octahedral B-site the
temperature range occupied by the spin-liquid regime narrows and TN increases.
To explain the experimental observations we considered magnetic anisotropy D or
third-neighbour exchange coupling J3 as degeneracy-breaking perturbations. We
conclude that Co(Al1-xCox)2O4 is below the theoretical critical point
J2/J1=1/8, and that magnetic anisotropy assists in selecting a collinear
long-range ordered ground state, which becomes more stable with increasing x
due to a higher efficiency of O-Co3+-O as an interaction path compared to
O-Al3+-O
Low temperature crystal structure and local magnetometry for the geometrically frustrated pyrochlore Tb2Ti2O7
We report synchrotron radiation diffraction and muon spin rotation (muSR)
measurements on the frustrated pyrochlore magnet Tb2Ti2O7. The powder
diffraction study of a crushed crystal fragment does not reveal any structural
change down to 4 K. The muSR measurements performed at 20 mK on a mosaic of
single crystals with an external magnetic field applied along a three-fold axis
are consistent with published a.c. magnetic-susceptibility measurements at 16
mK. While an inflection point could be present around an internal field
intensity slightly above 0.3 T, the data barely support the presence of a
magnetization plateau.Comment: To appear in the proceedings of the 13th International Conference on
Muon Spin Rotation, Relaxation and Resonance, Grindelwald, Switzerland, 1-6
June 201
Spin liquid in a single crystal of the frustrated diamond lattice antiferromagnet CoAl2O4
We study spin liquid in the frustrated diamond lattice antiferromagnet
CoAl2O4 by means of single crystal neutron scattering in zero and applied
magnetic field. The magnetically ordered phase appearing below TN=8 K remains
nonconventional down to 1.5 K. The magnetic Bragg peaks at the q=0 positions
remain broad and their profiles have strong Lorentzian contribution.
Additionally, they are connected by weak diffuse streaks along the
directions. These observations are explained within the spiral spin liquid
model as short-range magnetic correlations of spirals populated at these finite
temperatures, as the energy minimum around q=0 is flat and the energy of
excited states with q=(111) is low. The agreement is only qualitative, leading
us to suspect that microstructure effects are also important. Magnetic field
significantly perturbs spin correlations. The 1.5 K static magnetic moment
increases from 1.58 mB/Co at zero field to 2.08 mB/Co at 10 T, while the
magnetic peaks, being still broad, acquire almost Gaussian profile. Spin
excitations are rather conventional spin waves at zero field, resulting in the
exchange parameters J1=0.92(1) meV, J2=0.101(2) meV and the anisotropy term
D=-0.0089(2) meV for CoAl2O4. The application of a magnetic field leads to a
pronounced broadening of the excitations at the zone center, which at 10 T
appear gapless and nearly featureless
Instrumental profile of MYTHEN detector in Debye-Scherrer geometry
The main aberrations affecting data collected with 1D position sensitive detectors in Debye-Scherrer capillary geometry are examined, and analytical corrections proposed. The equations are implemented in two of the most advanced software based on the Rietveld and Whole Powder Pattern Modelling methods, respectively, for structure and microstructure analysis. Application to MYTHEN, a fast single photon counting detector developed at the Swiss Light Source, is discussed in detai
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