14 research outputs found
Magneto-structural properties of the layered quasi-2D triangular-lattice antiferromagnets CsCuClBr for = 0,1,2 and 4
We present a study of the magnetic susceptibility under variable
hydrostatic pressure on single crystals of CsCuClBr. This
includes the border compounds \textit{x} = 0 and 4, known as good realizations
of the distorted triangular-lattice spin-1/2 Heisenberg antiferromagnet, as
well as the isostructural stoichiometric systems CsCuClBr and
CsCuClBr. For the determination of the exchange coupling
constants and , data were fitted by a
model \cite{Schmidt2015}. Its application, validated for the
border compounds, yields a degree of frustration / = 0.47 for
CsCuClBr and / 0.63 - 0.78 for
CsCuClBr, making these systems particular interesting
representatives of this family. From the evolution of the magnetic
susceptibility under pressure up to about 0.4\,GPa, the maximum pressure
applied, two observations were made for all the compounds investigated here.
First, we find that the overall energy scale, given by +
), increases under pressure, whereas the ratio
/ remains unchanged in this pressure range. These experimental
observations are in accordance with the results of DFT calculations performed
for these materials. Secondly, for the magnetoelastic coupling constants,
extraordinarily small values are obtained. We assign these observations to a
structural peculiarity of this class of materials
Specific Heat Study of 1D and 2D Excitations in the Layered Frustrated Quantum Antiferromagnets CsCuClBr
We report an experimental and theoretical study of the low-temperature
specific heat and magnetic susceptibility of the layered anisotropic
triangular-lattice spin-1/2 Heisenberg antiferromagnets
CsCuClBr with = 0, 1, 2, and 4. We find that the ratio
of the exchange couplings ranges from 0.32 to , implying a
change (crossover or quantum phase transition) in the materials' magnetic
properties from one-dimensional (1D) behavior for to
two-dimensional (2D) behavior for behavior. For , realized for = 0, 1, and 4, we find a magnetic contribution to the
low-temperature specific heat, , consistent with spinon
excitations in 1D spin-1/2 Heisenberg antiferromagnets. Remarkably, for =
2, where implies a 2D magnatic character, we also observe
. This finding, which contrasts the prediction of made by standard spin-wave theories, shows that Fermi-like
statistics also plays a significant role for the magnetic excitations in
frustrated spin-1/2 2D antiferromagnets
Condiciones de germinación de semillas de "Briza subaristata" Lam. recolectadas en diferentes sitios de la Pampa Deprimida (Argentina)
Briza subaristata Lam. es una poácea perenne nativa, de valor forrajero en pastizales naturales de la pradera pampeana (Argentina). El objetivo de este ensayo fue establecer las condiciones de germinación de semillas de diferente origen geográfico. Para las condiciones de este ensayo se concluyó que el sitio de cosecha tuvo un efecto significativo en cuanto a la respuesta a los pre-tratamientos y temperaturas de germinación aplicados. En general, la pre-refrigeración no mejoró el porcentaje de germinación. En algunos sitios mejoró la germinación al utilizar KNO3 para humedecer el sustrato de germinación. Para estimar la calidad fisiológica de cariopsis de Briza subaristata con ocho o más meses poscosecha, temperaturas alternas 25-20 C en períodos de oscuridad/luz de 16/8 h, ausencia de pre-refrigeración y de KNO3, se presentaron como las más adecuadas para todas las muestras, independientemente del origen analizado
Planar Benzo[1,2-b:4,5-b′]dithiophene Derivatives Decorated with Nitronyl and Imino Nitroxides
Identification of cultivars of foxtail Mollet (Setaria italica (L.) Beauv.) from morphological and biochemical traits of their seed
The objective of this research was to characterise three cultivars of Setaria italica (L.) Beauv. "Foxtail millet": Ñandú INTA, Carapé INTA and Yaguané INTA by means of their seeds. The methodologies applied were: description of seed size, shape and weight, chemical changes to the phenol test, ferrous sulphate test and fluorescence tests, and polyacrylamide gel electrophoresis of proteins. ANOVA and comparison means test (Tukey, p<0.05) were performed. This study revealed that, with the exception of the fluorescence test, Yaguané, Carapé and Ñandú cultivars could be identified by using the set of methodologies considered.Fil: Pallares, I. N.. Universidad Nacional de Lomas de Zamora. Facultad de Ciencias Agrarias; ArgentinaFil: Ferrari, L.. Universidad Nacional de Lomas de Zamora. Facultad de Ciencias Agrarias; ArgentinaFil: Postulka, E. B.. Universidad Nacional de Lomas de Zamora. Facultad de Ciencias Agrarias; ArgentinaFil: Ritta, Monica Nora. Consejo Nacional de Investigaciones Científicas y Técnicas. Instituto de Biología y Medicina Experimental. Fundación de Instituto de Biología y Medicina Experimental. Instituto de Biología y Medicina Experimental; Argentina. Universidad Nacional de Lomas de Zamora. Facultad de Ciencias Agrarias; Argentin
Spin-dimer networks: engineering tools to adjust the magnetic interactions in biradicals
Magneto-structural correlations in stable organic biradicals have been studied on the example of weakly exchange coupled models with nitronyl nitroxide and imino nitroxide spin-carrying entities. Here, heteroatom substituted 2,2′-diaza- and 3,3′-diaza-tolane bridged biradicals were compared with the hydrocarbon analogue, while a biphenyl model with its 2,2′-bipyridine counterpart. For a 3,3′-diazatolane bridge the torsional angle between the nitronyl nitroxides and the pyridyl rings increased heavily (∼52–54°) leading to a smaller theoretical intra-dimer exchange coupling value. However, a very large antiferromagnetic coupling was obtained experimentally. This could be appropriately explained by the presence of dominating inter-dimer exchange between the molecules. For the bis(imino nitroxide) with tolane bridge a field induced ordered state between 1.8 to 4.3 T in AC-susceptibility measurements was observed. In terms of a Bose Einstein condensate (BEC) of triplons this phenomenon could be described as a magnetic field induced ordered phase with 3D character
Susceptibility measurements on a weakly coupled spin-dimersystem consisting of nitronyl-nitroxid stable biradicals
We present low-temperature susceptibility data on a spinS=12dimersystem consisting of nitronyl-nitroxid radicals which are bridged viatolan molecules. The material, exhibiting a double-layer structure,can be regarded as a quasi- 2D system. From SQUID magnetisationmeasurements on high-quality single crystals, an intra-dimer couplingconstant ofJintra/kB≈9.6 K can be determined. In addition, thedata reveal indications for an inter-dimer coupling of the order of 1 K.In order to look for magnetic field-induced ordering phenomena, AC-susceptibility measurements were performed down to temperatures aslow asT= 34 mK and magnetic fields up toB= 10.5 T. For temperatures belowT= 250 mK, a double-peak structure was observedat fields between 8 T and 9.5 T consistent with the expectation basedon the above-mentioned coupling constants. Furthermore, in the sametemperature range another anomaly aroundB= 4.5 T appears. Fora detailed understanding especially with regard to the dimensionalityof the interactions and the implications for the type of order that isrealized here, Quantum Monte Carlo simulations are underway