scholarly journals Magnetic charge and ordering in kagome spin ice

2012 ◽  
Vol 370 (1981) ◽  
pp. 5718-5737 ◽  
Author(s):  
Gia-Wei Chern ◽  
Oleg Tchernyshyov
Keyword(s):  
Intermediate Phase ◽  
Numerical Study ◽  
Magnetic Ordering ◽  
Charge Order ◽  
Spin Correlation ◽  
Temperature Phase ◽  
Spin Ice ◽  
Universality Classes ◽  
Lower Temperature ◽  
Two Stages

We present a numerical study of magnetic ordering in spin ice on kagome, a two-dimensional lattice of corner-sharing triangles. The magnet has six ground states and the ordering occurs in two stages, as one might expect for a six-state clock model. In spin ice with short-range interactions up to second neighbours, there is an intermediate critical phase separated from the paramagnetic and ordered phases by Kosterlitz–Thouless (KT) transitions. In dipolar spin ice, the intermediate phase has long-range order of staggered magnetic charges. The high- and low-temperature phase transitions are of the Ising and 3-state Potts universality classes, respectively. Freeze-out of defects in the charge order produce a very large spin correlation length in the intermediate phase. As a result of that, the lower-temperature transition appears to be of the KT type.

Modulated Structures in PbHfO3 Crystals at High-Pressure-High-Temperature Conditions

2018 ◽  
Vol 386 ◽  
pp. 149-155 ◽  
Author(s):  
Maria Knjazeva ◽  
Yurii Bronwald ◽  
Daria Andronikova ◽  
Georgiy Lityagin ◽  
Alexey Bosak ◽  
...  
Keyword(s):  
Intermediate Phase ◽  
Temperature Phase ◽  
X Ray Diffraction ◽  
Simultaneous Application ◽  
Intermediate Phases ◽  
High Pressure High Temperature ◽  
Modulated Structures ◽  
Higher Temperature ◽  
Lower Temperature ◽  
Oxygen Framework

Lead hafnate single crystals were characterized using single crystal x-ray diffraction under simultaneous application of hydrostatic pressure and high temperatures. The information on the structure of two intermediate phases, situated between antiferroelectric and paraelectric phases in the pressure-temperature phase diagram, has been obtained. The lower-temperature intermediate phase is characterized by incommensurate displacive modulations in Pb sublattice. The higher-temperature intermediate phase is characterized by oxygen framework distortion, primarily in the form of anti-phase tilts of the oxygen octahedra, which is also present in the lower-temperature intermediate phase.

Formation of Nanocrystalline Silicon in Tin-Doped Amorphous Silicon Films

2020 ◽  
Vol 65 (3) ◽  
pp. 236
Author(s):  
R. M. Rudenko ◽  
O. O. Voitsihovska ◽  
V. V. Voitovych ◽  
M. M. Kras’ko ◽  
A. G. Kolosyuk ◽  
...  
Keyword(s):  
Amorphous Silicon ◽  
Crystalline Silicon ◽  
Solid Phase ◽  
Nanocrystalline Silicon ◽  
Recrystallization Temperature ◽  
Nanocrystalline Phase ◽  
Silicon Phase ◽  
Silicon Nanocrystallites ◽  
Lower Temperature ◽  
Two Stages

The process of crystalline silicon phase formation in tin-doped amorphous silicon (a-SiSn) films has been studied. The inclusions of metallic tin are shown to play a key role in the crystallization of researched a-SiSn specimens with Sn contents of 1–10 at% at temperatures of 300–500 ∘C. The crystallization process can conditionally be divided into two stages. At the first stage, the formation of metallic tin inclusions occurs in the bulk of as-precipitated films owing to the diffusion of tin atoms in the amorphous silicon matrix. At the second stage, the formation of the nanocrystalline phase of silicon occurs as a result of the motion of silicon atoms from the amorphous phase to the crystalline one through the formed metallic tin inclusions. The presence of the latter ensures the formation of silicon crystallites at a much lower temperature than the solid-phase recrystallization temperature (about 750 ∘C). A possibility for a relation to exist between the sizes of growing silicon nanocrystallites and metallic tin inclusions favoring the formation of nanocrystallites has been analyzed.

Novel Magnetic Orders and Ice Phases in Frustrated Kondo-Lattice Models

SPIN ◽  
2015 ◽  
Vol 05 (02) ◽  
pp. 1540006 ◽  
Author(s):  
Gia-Wei Chern
Keyword(s):  
Berry Phase ◽  
Magnetic Moments ◽  
Lattice Models ◽  
Magnetic Ordering ◽  
Double Exchange ◽  
Salient Feature ◽  
Kondo Lattice ◽  
Spin Ice ◽  
Water Ice ◽  
Ising Magnets

We review recent theoretical progress in our understanding of electron-driven novel magnetic phases on frustrated lattices. Our specific focus is on Kondo-lattice or double-exchange models assuming finite magnetic moments localized at the lattice sites. A salient feature of systems with SU(2) symmetric local moments is the emergence of noncoplanar magnetic ordering driven by the conduction electrons. The complex spin textures then endow the electrons a nontrivial Berry phase, often giving rise to a topologically nontrivial electronic state. The second part of the review is devoted to the discussion of metallic spin ice systems, which are essentially frustrated Ising magnets with local spin ordering governed by the so-called ice rules. These rules are similar to those that describe proton configurations in solid water ice, hence the name "spin ice". The nontrivial spin correlations in the ice phase give rise to unusual electron transport properties in metallic spin-ice systems.

Differences and similarities among hypoxanthinium nitrate hydrate structures

2019 ◽  
Vol 75 (8) ◽  
pp. 1036-1044 ◽  
Author(s):  
Małgorzata Katarzyna Cabaj ◽  
Roman Gajda ◽  
Anna Hoser ◽  
Anna Makal ◽  
Paulina Maria Dominiak
Keyword(s):  
Room Temperature ◽  
Temperature Phase ◽  
X Ray Diffraction ◽  
Acta Cryst ◽  
X Ray ◽  
Nitrate Hydrate ◽  
Different Temperatures ◽  
Lower Temperature ◽  
Low Temperature Phase ◽  
Nitrate Anions

Crystals of hypoxanthinium (6-oxo-1H,7H-purin-9-ium) nitrate hydrates were investigated by means of X-ray diffraction at different temperatures. The data for hypoxanthinium nitrate monohydrate (C5H5N4O+·NO3 −·H2O, Hx1) were collected at 20, 105 and 285 K. The room-temperature phase was reported previously [Schmalle et al. (1990). Acta Cryst. C46, 340–342] and the low-temperature phase has not been investigated yet. The structure underwent a phase transition, which resulted in a change of space group from Pmnb to P21/n at lower temperature and subsequently in nonmerohedral twinning. The structure of hypoxanthinium dinitrate trihydrate (H3O+·C5H5N4O+·2NO3 −·2H2O, Hx2) was determined at 20 and 100 K, and also has not been reported previously. The Hx2 structure consists of two types of layers: the `hypoxanthinium nitrate monohydrate' layers (HX) observed in Hx1 and layers of Zundel complex H3O+·H2O interacting with nitrate anions (OX). The crystal can be considered as a solid solution of two salts, i.e. hypoxanthinium nitrate monohydrate, C5H5N4O+·NO3 −·H2O, and oxonium nitrate monohydrate, H3O+(H2O)·NO3 −.

Brittle Fracture Criteria Transferability Evaluation by Testing on Different Specimen Geometries

2008 ◽  
Author(s):  
S. Chapuliot ◽  
S. Marie
Keyword(s):  
Brittle Fracture ◽  
Critical Stress ◽  
Master Curve ◽  
Numerical Study ◽  
Fracture Criteria ◽  
Vessel Steel ◽  
Stress Criterion ◽  
Probability Of Fracture ◽  
Two Stages ◽  
Brittle Fracture Criteria

This paper describes an experimental and numerical study to assess the transposability of brittle fracture criteria from specimens of one type of geometry to another. The overall “master curve” approach, the Beremin model and a proposed model using the concept of critical stress were accordingly analysed. The experimental work supporting the analysis was made on 16MND5 reactor vessel steel. This was in the form of CT25 specimens, taken as the reference type, SENT specimens, ring specimens and CTpor specimens, which are CT specimens with a semi-elliptical surface defect. The analysis itself was made in two stages: the models were first calibrated on the basis of CT25 test results, then they were applied to specimens of other geometries. We then demonstrate that, in all cases, the models correctly replicated the variation of toughness (as measured on a CT25 specimen) with temperature. However, they all failed when applied to SENT and ring specimens, where calculation underestimates the probability of fracture. For CTpor specimens, the results are better, the master curve approach and the critical stress criterion give satisfactory results (but it has not yet been possible to apply the Beremin method). This paper concludes with a detailed analysis of the crack tip stress and strain fields, followed by an attempt to explain the differences between the different types of behaviour observed.

scholarly journals Is there a phase transition in the isotropic Heisenberg anti-ferromagnet on the triangular lattice?

2001 ◽  
Vol 79 (11-12) ◽  
pp. 1459-1461 ◽  
Author(s):  
W Stephan ◽  
B W Southern
Keyword(s):  
Phase Transition ◽  
Triangular Lattice ◽  
Finite Temperature ◽  
Easy Axis ◽  
Temperature Phase ◽  
Temperature Transition ◽  
Isotropic Model ◽  
Temperature Phase Transition ◽  
Lower Temperature ◽  
Xxz Heisenberg Model

The phase diagram of the classical anisotropic (XXZ) Heisenberg model on the two-dimensional triangular lattice is investigated using Monte Carlo methods. In the easy-axis limit, two finite-temperature vortex-unbinding transitions have been observed. In the easy-plane limit, there also appear to be two distinct finite-temperature phase transitions that are very close in temperature. The upper transition corresponds to an Ising-like chirality ordering and the lower temperature transition corresponds to a Kosterlitz–Thouless vortex-unbinding transition. These phase-transition lines all meet at the Heisenberg point and provide strong evidence that the isotropic model undergoes a novel finite-temperature phase transition. PACS Nos.: 75.10Hk, 75.40Mg

Ab initio structure determination and Rietveld refinement of a high-temperature phase of zirconium hydrogen phosphate and a new polymorph of zirconium pyrophosphate from in situ temperature-resolved powder diffraction data

2000 ◽  
Vol 56 (4) ◽  
pp. 618-625 ◽  
Author(s):  
Anne Marie Krogh Andersen ◽  
Poul Norby
Keyword(s):  
Powder Diffraction ◽  
Diffraction Data ◽  
Intermediate Phase ◽  
Temperature Phase ◽  
Powder Diffraction Data ◽  
Hydrogen Phosphate ◽  
Intermediate Phases ◽  
Zirconium Pyrophosphate ◽  
Phosphate Groups

The collected in situ temperature-resolved synchrotron powder data revealed that the transformation of the recently reported three-dimensional τ-Zr(HPO4)2 to cubic ZrP2O7 goes through two intermediate phases. The first intermediate phase, ρ-Zr(HPO4)2, is formed in a reversible phase transition at 598 K, which involves both rearrangement and disordering of the hydrogen phosphate groups of τ-Zr(HPO4)2. At 688 K condensation of the hydrogen phosphate groups leads to the formation of the second intermediate, a new polymorph of zirconium pyrophosphate (β-ZrP2O7). Heating above 973 K results in the gradual transformation of β-ZrP2O7 to cubic zirconium pyrophosphate (α-ZrP2O7). The crystal structures of the two intermediate phases were solved from the in situ powder diffraction data using direct methods and refined using the Rietveld method. Both phases are orthorhombic, space group Pnnm and Z = 2. The lattice parameters for the two phases are: ρ-Zr(HPO4)2: a = 8.1935 (2), b = 7.7090 (2), c = 5.4080 (1) Å; β-ZrP2O7: a = 8.3127 (5), b = 6.6389 (4), c = 5.3407 (3) Å. The formation mechanism for the new zirconium pyrophosphate polymorph, β-ZrP2O7, is discussed in relation to structurally restricted soft chemistry.

Sign in / Sign up

Export Citation Format

Share Document