925 research outputs found
Disorder effects in the quantum Heisenberg model: An Extended Dynamical mean-field theory analysis
We investigate a quantum Heisenberg model with both antiferromagnetic and
disordered nearest-neighbor couplings. We use an extended dynamical mean-field
approach, which reduces the lattice problem to a self-consistent local impurity
problem that we solve by using a quantum Monte Carlo algorithm. We consider
both two- and three-dimensional antiferromagnetic spin fluctuations and
systematically analyze the effect of disorder. We find that in three dimensions
for any small amount of disorder a spin-glass phase is realized. In two
dimensions, while clean systems display the properties of a highly correlated
spin-liquid (where the local spin susceptibility has a non-integer power-low
frequency and/or temperature dependence), in the present case this behavior is
more elusive unless disorder is very small. This is because the spin-glass
transition temperature leaves only an intermediate temperature regime where the
system can display the spin-liquid behavior, which turns out to be more
apparent in the static than in the dynamical susceptibility.Comment: 15 pages, 7 figure
Intrinsic susceptibility and bond defects in the novel 2D frustrated antiferromagnet BaSnZnCrGaO
We present microscopic and macroscopic magnetic properties of the highly
frustrated antiferromagnet BaSnZnCrGaO,
respectively probed with NMR and SQUID experiments. The -variation of the
intrinsic susceptibility of the Cr frustrated kagom\'{e} bilayer,
, displays a maximum around 45 K. The dilution of the magnetic
lattice has been studied in detail for . Novel dilution
independent defects, likely related with magnetic bond disorder, are evidenced
and discussed. We compare our results to SrCrGaO. Both
bond defects and spin vacancies do not affect the average susceptibility of the
kagom\'{e} bilayers.Comment: Published in Phys. Rev. Lett. 92, 217202 (2004). Only minor changes
as compared to previous version. 4 pages, 4 figure
Study of the Boson Peak and Fragility of Bioprotectant Glass-Forming Mixtures by Neutron Scattering
The biological relevance of trehalose, glycerol, and their mixtures in several anhydrobiotic and cryobiotic organisms has recently promoted both experimental and simulation studies. In addition, these systems are employed in different industrial fields, such as pharmaceutical and cosmetic industries, as additives in mixtures for cryopreservation and in several formulations. This review article shows an overview of Inelastic Neutron Scattering (INS) data, collected at different temperature values by the OSIRIS time-of-flight spectrometer at the ISIS Facility (Rutherford Appleton Laboratory, Oxford, UK) and by the IN4 and IN6 spectrometers at the Institut Laue Langevin (ILL, Grenoble, France), on trehalose/glycerol mixtures as a function of the glycerol content. The data analysis allows determining the Boson peak behavior and discussing the findings in terms of fragility in relation to the bioprotective action of trehalose and glycerol
Spin dynamics of heterometallic Cr7M wheels (M = Mn, Zn, Ni) probed by inelastic neutron scattering
Inelastic neutron scattering has been applied to the study of the spin
dynamics of Cr-based antiferromagnetic octanuclear rings where a finite total
spin of the ground state is obtained by substituting one Cr(III) ion (s = 3/2)
with Zn (s = 0), Mn (s = 5/2) or Ni (s = 1) di-cations. Energy and intensity
measurements for several intra-multiplet and inter-multiplet magnetic
excitations allow us to determine the spin wavefunctions of the investigated
clusters. Effects due to the mixing of different spin multiplets have been
considered. Such effects proved to be important to correctly reproduce the
energy and intensity of magnetic excitations in the neutron spectra. On the
contrary to what is observed for the parent homonuclear Cr8 ring, the symmetry
of the first excited spin states is such that anticrossing conditions with the
ground state can be realized in the presence of an external magnetic field.
Heterometallic Cr7M wheels are therefore good candidates for macroscopic
observations of quantum effects.Comment: 9 pages, 11 figures, submitted to Phys. Rev. B, corrected typos and
added references, one sentence change
Molecular Deuterion crystallitation under cuasi-1D confienment
ECNS 2015, Zaragoza (Spain), August 30th-September 4th 2015A particularly interesting aspect of Carbon Nanotubes is their use as nearly one-dimensional nano-containers. Apart of their possibilities for controlled chemistry in nano- fluidics devices new phenomena induced by confinement are also expected, such as liquid like ordered structures or exotic crystalline phases. Here, we present a series of neutron diffraction measurements (instrument D20, ILL, Grenoble) of molecular deuterium confined within Multiple Wall Carbon Nanotubes (MWCTNs). Bulk liquid D2 at its vapour pressure crystallises in an hcp structure at ~18.7 K. At low uptakes we have found a clear depression of the solidification temperature down to ~13.25 K. Interestingly, at the lowest uptake the diffraction pattern is consistent with the minimal fcc lattice compatible with a cylindrical symmetry.Peer Reviewe
Nematicidal and fertilizing effects of chicken manure, fresh and composted olive mill wastes on organic melon
Abstract
The fertilizing and nematicidal effects of three organic amendments were evaluated in a pot experiment on melon plants infested by the root-knot nematode Meloidogyne
incognita. A soil artificially infested with 4 eggs and juveniles/ ml soil of the nematode was amended with: a) virgin olive pomace (VOP); b) composted olive pomace (COP); c) chicken manure based fertilizer (CM) and d) chicken manure based fertilizer combined with the biological control agent Paecilomyces lilacinus strain 251, brand name BioAct WG (CMB). VOP was applied at doses of 11 (VOP-A), 22 (VOP-B) and 44 t/ha (VOP-C); COP at 4.5 (COP-A), 9 (COP-B) and 18 t/ha (COP-C); CM at 3 t/ha and CMB at 3 t/ha combined with 4 kg/ha of BioAct WG. Untreated soil was used as control. The treatments CM, CMB, VOP-B and COP-B were established on the basis of N requirement of melon plants (120 kg/ha) taking into account soil and amendments N availability. Two weeks later amendment application and nematode inoculation, the soil was poured in 4.8 l clay pots which were arranged in a greenhouse according to a randomized block design with ten replications for each treatment. A one-month old melon seedling (cv. Galia) was transplanted in each pot and organic farming management practices were used during the growing period. At the end of the experiment, 60 days after transplant, plants were uprooted and height, fresh and dry shoot and root weights were recorded. Root gall index, on the roots, caused by the nematode attack, was estimated according to a 0–5 scale. Final nematode population density and reproduction rate were also calculated for each pot. All data were subjected to statistical analysis of variance (ANOVA) and means compared according to Least Significant Difference's Test. Nematode population and root infestation were significantly suppressed by the addition of all amendments, compared to untreated control. However, CM and CMB resulted in a total more suppressive effect and in a significantly higher plant growth in comparison to all the other treatments. A significant correlation was found between root gall index and eggs and juveniles/g root and final nematode population density. No signifycant correlations were found between nematological parameters or plant growth parameters and amendment doses
Ga-NMR local susceptibility of the kagome-based magnet SrCr_9pGa_(12-9p)O_19. A high temperature study
We report a high- Ga-NMR study in the kagome-based antiferromagnetic
compound SrCrGaO (), and present a
refined mean-field analysis of the high T local NMR susceptibility of Cr
frustrated moments. We find that the intralayer kagome coupling is K,
and the interlayer coupling through non-kagome Cr moments is K. The ratio confirms the common belief that
the frustrated entity is a pyrochlore slab.Comment: 8 pages, 4 figures Conference paper: Highly Frustrated Magnetism
2000, Waterloo (Canada) Submitted to Canadian Journal of Physic
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