Search results for "Anisotropy"
showing 10 items of 912 documents
Morphology and magnetism of Fe on vicinal W(110) surfaces with different step orientation
2000
Abstract Nanostructures of monolayer height of single-crystalline Fe(1 1 0) films were grown on stepped W(1 1 0) surfaces. The growth mode strongly depends on the step orientation of the substrate. Continuous stripes are formed at steps along the [1 0 0] direction whereas triangular shaped islands grow on substrates with [1 −1 0]-oriented step edges. No ferromagnetic order was found in submonolayer films grown on [1 −1 0]-steps. The nanostripe array on [1 0 0] steps shows a ferromagnetic phase-transition with a critical behavior different from the Ising-like phase transition observed for submonolayer films grown on smooth W(1 1 0). The magnetic easy axis in the samples is oriented parallel …
Quantum magnetism of spin-ladder compounds with trapped-ion crystals
2012
Abstract The quest for experimental platforms that allow for the exploration, and even control, of the interplay of low dimensionality and frustration is a fundamental challenge in several fields of quantum many-body physics, such as quantum magnetism. Here, we propose the use of cold crystals of trapped ions to study a variety of frustrated quantum spin ladders. By optimizing the trap geometry, we show how to tailor the low dimensionality of the models by changing the number of legs of the ladders. Combined with a method for selectively hiding ions provided by laser addressing, it becomes possible to synthesize stripes of both triangular and Kagome lattices. Besides, the degree of frustrat…
Dipolar superferromagnetism in monolayer nanostripes of Fe(110) on vicinal W(110) surfaces
1998
By epitaxial growth of Fe on a vicinal W~110! substrate, densely spaced and continuous monolayer stripes of Fe~110! were prepared, directed along @001#. They exhibit a sharp phase transition to ferromagnetic order, free from relaxations. The magnetic easy axis is in the plane, but along @110# that means across the stripes. This cross magnetization induces ferromagnetic dipolar coupling between the spin blocks in adjacent stripes, which are preformed by exchange interactions. The resulting superferromagnetic phase transition is therefore driven by dipolar interactions. @S0163-1829~98!52002-4#
Anisotropic carrier diffusion in single MAPbI(3) grains correlates to their twin domains
2020
Polycrystalline thin films and single crystals of hybrid perovskites – a material group successfully used for photovoltaic and optoelectronic applications – reportedly display heterogeneous charge carrier dynamics often attributed to grain boundaries or crystalline strain. Here, we locally resolved the carrier diffusion in large, isolated methylammonium lead iodide (MAPbI3) grains via spatial- and time-resolved photoluminescence microscopy. We found that the anisotropic carrier dynamics directly correlate with the arrangement of ferroelastic twin domains. Comparing diffusion constants parallel and perpendicular to the domains showed carriers diffuse around 50–60% faster along the parallel d…
Experimental and theoretical study of dense YBO3 and the influence of non-hydrostaticity.
2021
[EN] YBO3 is used in photonics applications as a host for red phosphors due to its desirable chemical stability, high quantum efficiency and luminescence intensity. Despite its fundamental thermodynamic nature, the isothermal bulk modulus of YBO3 has remained a contentious issue due to a lack of comprehensive experimental and theoretical data and its vibrational modes are far from being understood. Here, we present an experimental-theoretical structural and vibrational study of YBO3. From structural data obtained from synchrotron X-ray diffraction data and ab initio calculations, we have determined the YBO3 bulk modulus, isothermal compressibility tensor and pressure-volume (P-V) equation o…
Anisotropies and magnetic phase transitions in insulating antiferromagnets determined by a Spin-Hall magnetoresistance probe
2019
Antiferromagnets possess a number of intriguing and promising properties for electronic devices, which include a vanishing net magnetic moment and thus insensitivity to large magnetic fields and characteristic terahertz frequency dynamics. However, probing the antiferromagnetic ordering is challenging without synchrotron-based facilities. Here, we determine the material parameters of the insulating iron oxide hematite, α-Fe2O3, using the surface sensitive spin-Hall magnetoresistance (SMR). Combined with a simple analytical model, we extract the antiferromagnetic anisotropies and the bulk Dzyaloshinskii-Moriya field over a wide range of temperatures and magnetic fields. Across the Morin phas…
Ellipsometric studies of behenic acid at the air-water interface
1991
The rich phase behaviour of monolayers of behenic acid (=docosanoic acid) has been analyzed by null ellipsometry in isothermic and isobaric measurements. By using structural data known from x-ray measurements the anisotropy and refractive indices in the vicinity of the S-CS phase transition have been calculated with a minimum of model assumptions. The calculated values are: nsx=1.47. ncsx=1.48. nsz=1.54. ncsz=1.55. and anisotropy γ=nx/nz ≈0.95. It is also shown that ellipsometry is a very sensitive and convenient method of detecting phase transitions. Its value for quantifying the roughness of the monolayer in the close vicinity of phase transitions due to thickness and density fluctuations…
Crystal nuclei in melts: A Monte Carlo simulation of a model for attractive colloids
2015
As a model for a suspension of hard-sphere like colloidal particles where small nonadsorbing dissolved polymers create a depletion attraction, we introduce an effective colloid-colloid potential closely related to the Asakura-Oosawa model but that does not have any discontinuities. In simulations, this model straightforwardly allows the calculation of the pressure from the Virial formula, and the phase transition in the bulk from the liquid to crystalline solid can be accurately located from a study where a stable coexistence of a crystalline slab with a surrounding liquid phase occurs. For this model, crystalline nuclei surrounded by fluid are studied both by identifying the crystal-fluid …
On the order of the herringbone transition of N2 on graphite: a Monte Carlo study
1993
Using the anisotropic planar-rotor model we investigate the herringbone phase transition of N2 in the (√3 × √3)R30° commensurate phase on graphite by large scale Monte Carlo simulations. The effective correlation length ξ is measured near the transition temperature T0. The data, extrapolated to T0, yield a large but finite ξ at T0 demonstrating that the herringb ordering is a weak first order transition.
Experimental and Theoretical Study of SbPO 4 under Compression
2019
SbPO4 is a complex monoclinic layered material characterized by a strong activity of the non-bonding lone electron pair (LEP) of Sb. The strong cation LEP leads to the formation of layers piled up along the a-axis and linked by weak Sb-O electrostatic interactions. In fact, Sb is 4-fold coordination with O similar to what occurs with the P-O coordination, despite the large difference of ionic radii and electronegativity between both elements. Here we report a joint experimental and theoretical study of the structural and vibrational properties of SbPO4 at high pressure. We show that SbPO4 is not only one of the most compressible phosphates but also one of the most compressible compounds of …