scholarly journals Monopolar and dipolar relaxation in spin ice Ho2Ti2O7

2021 ◽  
Vol 7 (25) ◽  
pp. eabg0908
Author(s):  
Yishu Wang ◽  
T. Reeder ◽  
Y. Karaki ◽  
J. Kindervater ◽  
T. Halloran ◽  
...  
Keyword(s):  
Bound States ◽  
Elevated Temperatures ◽  
Magnetic Monopoles ◽  
Atomic Scale ◽  
Relaxation Processes ◽  
Spin Ice ◽  
Coulomb Interactions ◽  
Relaxation Dynamics ◽  
Dipolar Relaxation ◽  
New Class

Ferromagnetically interacting Ising spins on the pyrochlore lattice of corner-sharing tetrahedra form a highly degenerate manifold of low-energy states. A spin flip relative to this “spin-ice” manifold can fractionalize into two oppositely charged magnetic monopoles with effective Coulomb interactions. To understand this process, we have probed the low-temperature magnetic response of spin ice to time-varying magnetic fields through stroboscopic neutron scattering and SQUID magnetometry on a new class of ultrapure Ho2Ti2O7 crystals. Covering almost 10 decades of time scales with atomic-scale spatial resolution, the experiments resolve apparent discrepancies between prior measurements on more disordered crystals and reveal a thermal crossover between distinct relaxation processes. Magnetic relaxation at low temperatures is associated with monopole motion through the spin-ice vacuum, while at elevated temperatures, relaxation occurs through reorientation of increasingly spin-like monopolar bound states. Spin fractionalization is thus directly manifest in the relaxation dynamics of spin ice.

Contributions of Dipolar Relaxation Processes and Ionic Transport to the Response of Liquids to Electrical Perturbation Fields

2011 ◽  
Vol 115 (19) ◽  
pp. 5730-5740 ◽  
Author(s):  
M. J. Sanchis ◽  
P. Ortiz-Serna ◽  
M. Carsí ◽  
R. Díaz-Calleja ◽  
E. Riande ◽  
...  
Keyword(s):  
Ionic Transport ◽  
Relaxation Processes ◽  
Dipolar Relaxation

Thionation reactions of 2-pyrrole carboxylates

RSC Advances ◽  
2016 ◽  
Vol 6 (74) ◽  
pp. 69691-69697 ◽  
Author(s):  
Brandon R. Groves ◽  
Deborah A. Smithen ◽  
T. Stanley Cameron ◽  
Alison Thompson
Keyword(s):  
Elevated Temperatures ◽  
Lawesson’S Reagent ◽  
New Class ◽  
Lawesson's Reagent

Reaction of 2-pyrrole carboxylates with Lawesson's reagent at elevated temperatures results in the corresponding thionoesters, concurrent with the production of a new class of pyrrole annulated with the (1,3,2)-thiazaphospholidine unit.

Brittle-ductile transition of titanium aluminides, alloyed by β-phase stabilization elements

2020 ◽  
Vol 2020 (01) ◽  
pp. 86-97
Author(s):  
M. V. Remez ◽  
◽  
Yu. M. Podrezov ◽  
V. I. Danylenko ◽  
M. I. Danylenko ◽  
...  
Keyword(s):  
Plastic Zone ◽  
Grain Boundaries ◽  
Titanium Aluminides ◽  
Elevated Temperatures ◽  
Rate Sensitivity ◽  
Relaxation Processes ◽  
Main Role ◽  
Β Phase ◽  
Brittle Ductile Transition ◽  
Phase Stabilization

The temperature, structural, and rate sensitivity of the plasticity characteristics in γ-tita¬nium aluminides with different Al contents, doped with β-phase stabilization elements, are studied. Particular attention is paid to dislocation mechanisms that control the brittle-plastic transition. The main role of grain boundaries in the formation of plasticity characteristics is demonstrated. At low temperatures, the grain boundaries stop propagation of brittle transgranular cracks and confine the development of the plastic zone beyond the boundaries of an individual grain, creating the prerequisites for fracture in the microdeformation level. At elevated temperatures, the boundaries contribute to the formation of dislocations pile-up in the plastic zone with a stress concentration required to set off the Frank-Reed sources and the displacement of the plastic zone beyond the boundaries of an individual grain, changing its configuration and stress distribution and inhibiting the propagation of cracks. Acceleration of rela¬xation processes in the vicinity of the crack’s tip creates the prerequisites for the development of macrodeformation. Local relaxation processes at the crack’s tip contribute to high speed sensitivity of the plasticity characteristics. This effect has important practical consequences, since there is a temperature region near the upper working temperature of γ-TiAl alloys, where the stress value remains high (yield strength σ02 ~700 MPa and ultimate stress σul ~ 1200 MPa at bending tests) regardless of the strain rate, while deformation sharply increases at low speeds. As a result, it is possible to achieve a combination of high strength and ductility during creep tests. In samples tested by tension with low speed (10-5 s-1) the neck formation take a place. Deformation occurs by the dislocation-twinning mechanisms. At small deformations (7%) a twinning mechanism is preferable. Concentration of dislocations sharply increases at large deformations (32%) with formation of dislocation clusters. Stress relaxation on the boundary between γ-phase twins and α2-lamella, occurs by macroscopic shift on α2-lamella. Keywords: γ-titanium-aluminides, structure, strength, plasticity, brittle-ductile transition, temperature and rate sensitivity.

Transport through several four-quantum-dot topological structures

2021 ◽  
pp. 2150393
Author(s):  
Qingshuang Zhi ◽  
Kongfa Chen ◽  
Zelong He
Keyword(s):  
Quantum Dot ◽  
Coupling Strength ◽  
Bound States ◽  
Resonance Peak ◽  
Coulomb Interactions ◽  
Many Body ◽  
Body Effect ◽  
Topological Structures ◽  
Resonance Band ◽  
Interdot Coupling

In this paper, several four-quantum-dot topological structures are designed. The influence of the interdot coupling strength and intradot Coulomb interactions on the conductance is discussed. The location of the anti-resonance band can be manipulated by tuning the interdot coupling strength, which suggests a physical scheme of an effective quantum switch. The Fano anti-resonance peak may evolve into a resonance peak. For the particular value of the interdot coupling strength, two Fano anti-resonances collapse and bound states in the continuum are formed. Moreover, many-body effect makes the number of anti-resonance bands increase. This study provides a theoretical basis for the design of quantum computing devices.

scholarly journals A Bis-Monophospholyl Dysprosium Cation Showing Magnetic Hysteresis at 48 Kelvin

2019 ◽  
Author(s):  
Peter Evans ◽  
Daniel Reta ◽  
George F. S. Whitehead ◽  
Nicholas Chilton ◽  
David Mills
Keyword(s):  
Data Storage ◽  
Single Molecule ◽  
Structural Changes ◽  
Elevated Temperatures ◽  
Spin Dynamics ◽  
Magnetic Hysteresis ◽  
Relaxation Times ◽  
Magnetic Memory ◽  
Relaxation Processes ◽  
Potential Applications

Single-molecule magnets (SMMs) have potential applications in high-density data storage, but magnetic relaxation times at elevated temperatures must be increased to make them practically useful. <i>Bis</i>-cyclopentadienyl lanthanide sandwich complexes have emerged as the leading candidates for SMMs that show magnetic memory at liquid nitrogen temperatures, but the relaxation mechanisms mediated by aromatic C<sub>5</sub> rings have not been fully established. Here we synthesise a <i>bis</i>-monophospholyl dysprosium SMM [Dy(Dtp)<sub>2</sub>][Al{OC(CF<sub>3</sub>)<sub>3</sub>}<sub>4</sub>] (<b>1</b>, Dtp = {P(C<sup>t</sup>BuCMe)<sub>2</sub>}) by the treatment of <i>in situ</i>-prepared “[Dy(Dtp)<sub>2</sub>(C<sub>3</sub>H<sub>5</sub>)]” with [HNEt<sub>3</sub>][Al{OC(CF<sub>3</sub>)<sub>3</sub>}<sub>4</sub>]. SQUID magnetometry reveals that <b>1</b> has an effective barrier to magnetisation reversal of 1,760 K (1,223 cm<sup>–1</sup>) and magnetic hysteresis up to 48 K. <i>Ab initio</i> calculation of the spin dynamics reveal that transitions out of the ground state are slower in <b>1</b> than in the first reported dysprosocenium SMM, [Dy(Cp<sup>ttt</sup>)<sub>2</sub>][B(C<sub>6</sub>F<sub>5</sub>)<sub>4</sub>] (Cp<sup>ttt</sup> = C<sub>5</sub>H<sub>2</sub><sup>t</sup>Bu<sub>3</sub>-1,2,4), however relaxation is faster in <b>1</b> overall due to the compression of electronic energies and to vibrational modes being brought on-resonance by the chemical and structural changes introduced by the <i>bis</i>-Dtp framework. With the preparation and analysis of <b>1</b> we are thus able to further refine our understanding of relaxation processes operating in <i>bis</i>-C<sub>5</sub>/C<sub>4</sub>P sandwich lanthanide SMMs, which is the necessary first step towards rationally achieving higher magnetic blocking temperatures in these systems in future.

scholarly journals The Influence of the Ceramic Nanoparticles on the Thermoplastic Polymers Matrix: Their Structural, Optical, and Conductive Properties

Polymers ◽  
2021 ◽  
Vol 13 (16) ◽  
pp. 2773
Author(s):  
Ion Smaranda ◽  
Andreea Nila ◽  
Paul Ganea ◽  
Monica Daescu ◽  
Irina Zgura ◽  
...  
Keyword(s):  
Weight Ratio ◽  
Relaxation Processes ◽  
X Ray Diffraction ◽  
Thermoplastic Polymers ◽  
Dipolar Relaxation ◽  
Ceramic Nanoparticles ◽  
Preferential Adsorption ◽  
Conductive Properties ◽  
Ir Bands ◽  
Pl Quenching

This paper prepared composites under the free membranes form that are based on thermoplastic polymers of the type of polyurethane (TPU) and polyolefin (TPO), which are blended in the weight ratio of 2:1, and ceramic nanoparticles (CNs) such as BaSrTiO3 and SrTiO3. The structural, optical, and conductive properties of these new composite materials are reported. The X-ray diffraction studies highlight a cubic crystalline structure of these CNs. The main variations in the vibrational properties of the TPU:TPO blend induced by CNs consist of the following: (i) the increase in the intensity of the Raman line of 1616 cm−1; (ii) the down-shift of the IR band from 800 to 791 cm−1; (iii) the change of the ratio between the absorbance of IR bands localized in the spectral range 950–1200 cm−1; and (iv) the decrease in the absorbance of the IR band from 1221 cm−1. All these variations were correlated with a preferential adsorption of thermoplastic polymers on the CNs surface. A photoluminescence (PL) quenching process of thermoplastic polymers is demonstrated to occur in the presence of CNs. The anisotropic PL measurements have highlighted a change in the angle of the binding of the TPU:TPO blend, which varies from 23.7° to ≈49.3° and ≈53.4°, when the concentration of BaSrTiO3 and SrTiO3 CNs, respectively, is changed from 0 to 25 wt. %. Using dielectric spectroscopy, two mechanisms are invoked to take place in the case of the composites based on TPU:TPO blends and CNs, i.e., one regarding the type of the electrical conduction and another specifying the dielectric–dipolar relaxation processes.

scholarly journals Magnetic monopoles in spin ice

Nature ◽  
2008 ◽  
Vol 451 (7174) ◽  
pp. 42-45 ◽  
Author(s):  
C. Castelnovo ◽  
R. Moessner ◽  
S. L. Sondhi
Keyword(s):  
Magnetic Monopoles ◽  
Spin Ice

scholarly journals Ionic conductivity of deep eutectic solvents: the role of orientational dynamics and glassy freezing

2019 ◽  
Vol 21 (13) ◽  
pp. 6801-6809 ◽  
Author(s):  
Daniel Reuter ◽  
Catharina Binder ◽  
Peter Lunkenheimer ◽  
Alois Loidl
Keyword(s):  
Ionic Conductivity ◽  
Dielectric Spectroscopy ◽  
Deep Eutectic Solvents ◽  
Relaxation Dynamics ◽  
Dipolar Relaxation ◽  
Orientational Dynamics

Dielectric spectroscopy reveals that the ionic conductivity of deep eutectic solvents is closely coupled to their reorientational dipolar relaxation dynamics.

scholarly journals Valley interference and spin exchange at the atomic scale in silicon

2020 ◽  
Vol 11 (1) ◽  
Author(s):  
B. Voisin ◽  
J. Bocquel ◽  
A. Tankasala ◽  
M. Usman ◽  
J. Salfi ◽  
...  
Keyword(s):  
Spin Exchange ◽  
Atomic Scale ◽  
Scanning Tunneling ◽  
Coulomb Interactions ◽  
Tunneling Microscopy ◽  
Quantum Process ◽  
Strongly Coupled ◽  
Heisenberg Spin ◽  
Heisenberg Spin Exchange ◽  
Complex Phenomena

AbstractTunneling is a fundamental quantum process with no classical equivalent, which can compete with Coulomb interactions to give rise to complex phenomena. Phosphorus dopants in silicon can be placed with atomic precision to address the different regimes arising from this competition. However, they exploit wavefunctions relying on crystal band symmetries, which tunneling interactions are inherently sensitive to. Here we directly image lattice-aperiodic valley interference between coupled atoms in silicon using scanning tunneling microscopy. Our atomistic analysis unveils the role of envelope anisotropy, valley interference and dopant placement on the Heisenberg spin exchange interaction. We find that the exchange can become immune to valley interference by engineering in-plane dopant placement along specific crystallographic directions. A vacuum-like behaviour is recovered, where the exchange is maximised to the overlap between the donor orbitals, and pair-to-pair variations limited to a factor of less than 10 considering the accuracy in dopant positioning. This robustness remains over a large range of distances, from the strongly Coulomb interacting regime relevant for high-fidelity quantum computation to strongly coupled donor arrays of interest for quantum simulation in silicon.

Ultrafast spectroscopic investigations of the relaxation dynamics of a new class of water-soluble Coumarins

1996 ◽  
Author(s):  
L. Cassara ◽  
T. Gustavsson ◽  
S. Pommeret ◽  
J.-C. Mialocq ◽  
J. Chalom ◽  
...  
Keyword(s):  
Water Soluble ◽  
Relaxation Dynamics ◽  
New Class ◽  
Spectroscopic Investigations
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