21 research outputs found
Two geometrically frustrated magnets studied by neutron diffraction
In the pyrochlore compounds, TbTiO and TbSnO, only
the Tb ions are magnetic. They exhibit quite abnormal -- and, in view of
their chemical similarity, strikingly different -- magnetic behaviour, as
probed by neutron diffraction at ambient and applied pressure.
TbTiO is a cooperative paramagnet (`spin liquid'), without long
range order at ambient pressure; however, it does become ordered under
pressure. By contrast, TbSnO enters an "ordered spin ice" state
already at ambient pressure. We analyse a simple model which already clearly
exhibits some of the qualitative features observed experimentally. Overall,
comparing these two compounds emphasizes the power of small perturbations in
selecting low-temperature states in geometrically frustrated systems.Comment: 6 pages, 4 figures, International Conference on Neutron Scattering
Sydney(2005
Influence of hydrogen supply on emissive characteristics of pig with metal-hydride cathode
The experimental studies of the Penning-type charged particle source with metal hydride cathode are presented. In order to determine the mechanisms responsible for the emission of negative particles in the axial direction, the influence of different hydrogen feeding methods were studied. To simulate hydrogen desorption the cathode of special design was applied and to force only hydrogen ion-stimulated desorption the forced cooling metal hydride cathode was used.Представлены результаты экспериментального исследования источника заряженных частиц пеннинговского типа с металлогидридным катодом. С целью определения факторов, ответственных за эмиссию отрицательных частиц в аксиальном направлении, изучено влияние разных способов напуска водорода в ячейку. Для имитации десорбции применены катоды специальной конструкции и ион-стимулированная десорбция водорода за счет принудительного охлаждения металлогидридного катода.Представлено результати експериментального дослідження джерела заряджених частинок пенінговського типу з металогідридним катодом. З метою визначення факторів, що відповідають за емісію негативних частинок в аксіальному напрямку, вивчено вплив різних способів напуску водню в проміжок. Для імітації десорбції застосовані катода спеціальної конструкції і іон-стимульована десорбція водню за рахунок примусового охолодження металогідридного катоду
Magnetic fluctuations in frustrated Laves hydrides R(Mn_{1-x}Al_{x})_{2}H_{y}
By neutron scattering, we have studied the spin correlations and spin
fluctuations in frustrated Laves hydrides, where magnetic disorder sets in the
topologically frustrated Mn lattice. Below the transition towards short range
magnetic order, static spin clusters coexist with fluctuating and alsmost
uncorrelated spins. The magnetic response shows a complexe lineshape, connected
with the presence of the magnetic inhomogeneities. Its analysis shows the
existence of two different processes, relaxation and local excitations, for the
spin fluctuations below the transition. The paramagnetic fluctuations are
discussed in comparison with classical spin glasses, cluster glasses, and non
Fermi liquid itinerant magnets
Magnetic Structure Of Cerhin5 As A Function Of Pressure And Temperature
We report magnetic neutron-diffraction and electrical resistivity studies on single crystals of the heavy-fermion antiferromagnet CeRhIn5 at pressures up to 2.3 GPa. These experiments show that the staggered moment of Ce and the incommensurate magnetic structure change weakly with applied pressure up to 1.63 GPa, where resistivity, specific heat and nuclear quadrupole resonance measurements confirm the presence of bulk superconductivity. This work places important constraints on an interpretation of the relationship between antiferromagnetism and unconventional superconductivity in CeRhIn 5.692244031244036Heffner, R.H., Norman, M.R., (1996) Comments Condens. Matter Phys., 17, p. 361Stewart, G.R., (2001) Rev. Mod. 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Interlayer Exchange Coupling Mediated by Valence Band Electrons
The interlayer exchange coupling mediated by valence band electrons in
all-semiconductor IV-VI magnetic/nonmagnetic superlattices is studied
theoretically. A 3D tight-binding model, accounting for the band and magnetic
structure of the constituent superlattice components is used to calculate the
spin-dependent part of the total electronic energy. The antiferromagnetic
coupling between ferromagnetic layers in EuS/PbS superlattices is obtained, in
agreement with the experimental evidences. The results obtained for the
coupling between antiferromagnetic layers in EuTe/PbTe superlattices are also
presented.Comment: 8 pages, 6 figures, to be submitted to Phys.Rev.
Electronic Structure of the Complex Hydride NaAlH4
Density functional calculations of the electronic structure of the complex
hydride NaAlH4 and the reference systems NaH and AlH3 are reported. We find a
substantially ionic electronic structure for NaAlH4, which emphasizes the
importance of solid state effects in this material. The relaxed hydrogen
positions in NaAlH4 are in good agreement with recent experiment. The
electronic structure of AlH3 is also ionic. Implications for the binding of
complex hydrides are discussed.Comment: 4 pages, 5 figure
Magnetic interactions in EuTe epitaxial layers and EuTe/PbTe superlattices
The magnetic properties of antiferromagnetic (AFM) EuTe epitaxial layers and
short period EuTe/PbTe superlattices (SLs), grown by molecular beam epitaxy on
(111) BaF substrates, were studied by magnetization and neutron diffraction
measurements. Considerable changes of the N\'eel temperature as a function of
the EuTe layer thickness as well as of the strain state were found. A mean
field model, taking into account the variation of the exchange constants with
the strain-induced lattice distortions, and the nearest neighbor environment of
a Eu atoms, was developed to explain the observed changes in wide
range of samples. Pronounced interlayer magnetic correlations have been
revealed by neutron diffraction in EuTe/PbTe SLs with PbTe spacer thickness up
to 60 \AA. The observed diffraction spectra were analyzed, in a kinematical
approximation, assuming partial interlayer correlations characterized by an
appropriate correlation parameter. The formation of interlayer correlations
between the AFM EuTe layers across the nonmagnetic PbTe spacer was explained
within a framework of a tight-binding model. In this model, the interlayer
coupling stems from the dependence of the total electronic energy of the
EuTe/PbTe SL on the spin configurations in adjacent EuTe layers. The influence
of the EuTe and PbTe layer thickness fluctuations, inherent in the epitaxial
growth process, on magnetic properties and interlayer coupling is discussed.Comment: 17 pages, 19 figures, accepted to PR