scholarly journals Block–spiral magnetism: An exotic type of frustrated order

2020 ◽  
Vol 117 (28) ◽  
pp. 16226-16233 ◽  
Author(s):  
J. Herbrych ◽  
J. Heverhagen ◽  
G. Alvarez ◽  
M. Daghofer ◽  
A. Moreo ◽  
...  
Keyword(s):  
Neutron Scattering ◽  
Degrees Of Freedom ◽  
Magnetic Order ◽  
Frustrated Magnets ◽  
Magnetic Islands ◽  
Hubbard Models ◽  
Extensive Field ◽  
Mott Phase ◽  
Low Dimensional ◽  
Spiral State

Competing interactions in quantum materials induce exotic states of matter such as frustrated magnets, an extensive field of research from both the theoretical and experimental perspectives. Here, we show that competing energy scales present in the low-dimensional orbital-selective Mott phase (OSMP) induce an exotic magnetic order, never reported before. Earlier neutron-scattering experiments on iron-based 123 ladder materials, where OSMP is relevant, already confirmed our previous theoretical prediction of block magnetism (magnetic order of the form↑↑↓↓). Now we argue that another phase can be stabilized in multiorbital Hubbard models, the block–spiral state. In this state, the magnetic islands form a spiral propagating through the chain but with the blocks maintaining their identity, namely rigidly rotating. The block–spiral state is stabilized without any apparent frustration, the common avenue to generate spiral arrangements in multiferroics. By examining the behavior of the electronic degrees of freedom, parity-breaking quasiparticles are revealed. Finally, a simple phenomenological model that accurately captures the macroscopic spin spiral arrangement is also introduced, and fingerprints for the neutron-scattering experimental detection are provided.

scholarly journals A chiral switchable photovoltaic ferroelectric 1D perovskite

2020 ◽  
Vol 6 (9) ◽  
pp. eaay4213 ◽  
Author(s):  
Yang Hu ◽  
Fred Florio ◽  
Zhizhong Chen ◽  
W. Adam Phelan ◽  
Maxime A. Siegler ◽  
...  
Keyword(s):  
Electric Fields ◽  
Mirror Symmetry ◽  
Degrees Of Freedom ◽  
Electrical Measurements ◽  
Temperature Dependent ◽  
Paraelectric Phase Transition ◽  
Strongly Coupled ◽  
Yield Phenomena ◽  
Hybrid Perovskite ◽  
Low Dimensional

Spin and valley degrees of freedom in materials without inversion symmetry promise previously unknown device functionalities, such as spin-valleytronics. Control of material symmetry with electric fields (ferroelectricity), while breaking additional symmetries, including mirror symmetry, could yield phenomena where chirality, spin, valley, and crystal potential are strongly coupled. Here we report the synthesis of a halide perovskite semiconductor that is simultaneously photoferroelectricity switchable and chiral. Spectroscopic and structural analysis, and first-principles calculations, determine the material to be a previously unknown low-dimensional hybrid perovskite (R)-(−)-1-cyclohexylethylammonium/(S)-(+)-1 cyclohexylethylammonium) PbI3. Optical and electrical measurements characterize its semiconducting, ferroelectric, switchable pyroelectricity and switchable photoferroelectric properties. Temperature dependent structural, dielectric and transport measurements reveal a ferroelectric-paraelectric phase transition. Circular dichroism spectroscopy confirms its chirality. The development of a material with such a combination of these properties will facilitate the exploration of phenomena such as electric field and chiral enantiomer–dependent Rashba-Dresselhaus splitting and circular photogalvanic effects.

scholarly journals Emergent long-range magnetic order in ultrathin (111)-oriented LaNiO3 films

2021 ◽  
Vol 6 (1) ◽  
Author(s):  
Margaret M. Kane ◽  
Arturas Vailionis ◽  
Lauren J. Riddiford ◽  
Apurva Mehta ◽  
Alpha T. N’Diaye ◽  
...  
Keyword(s):  
Long Range ◽  
Degrees Of Freedom ◽  
Magnetic Order ◽  
Magnetic Ordering ◽  
Anomalous Hall Effect ◽  
X Ray Diffraction ◽  
X Ray ◽  
Range Magnetic Order ◽  
Film Substrate ◽  
Long Range Magnetic Order

AbstractThe emergence of ferromagnetism in materials where the bulk phase does not show any magnetic order demonstrates that atomically precise films can stabilize distinct ground states and expands the phase space for the discovery of materials. Here, the emergence of long-range magnetic order is reported in ultrathin (111) LaNiO3 (LNO) films, where bulk LNO is paramagnetic, and the origins of this phase are explained. Transport and structural studies of LNO(111) films indicate that NiO6 octahedral distortions stabilize a magnetic insulating phase at the film/substrate interface and result in a thickness-dependent metal–insulator transition at t = 8 unit cells. Away from this interface, distortions relax and bulk-like conduction is regained. Synchrotron x-ray diffraction and dynamical x-ray diffraction simulations confirm a corresponding out-of-plane unit-cell expansion at the interface of all films. X-ray absorption spectroscopy reveals that distortion stabilizes an increased concentration of Ni2+ ions. Evidence of long-range magnetic order is found in anomalous Hall effect and magnetoresistance measurements, likely due to ferromagnetic superexchange interactions among Ni2+–Ni3+ ions. Together, these results indicate that long-range magnetic ordering and metallicity in LNO(111) films emerges from a balance among the spin, charge, lattice, and orbital degrees of freedom.

scholarly journals Optimizing the structure and movement of a robotic bat with biological kinematic synergies

2018 ◽  
Vol 37 (10) ◽  
pp. 1233-1252 ◽  
Author(s):  
Jonathan Hoff ◽  
Alireza Ramezani ◽  
Soon-Jo Chung ◽  
Seth Hutchinson
Keyword(s):  
Principal Component Analysis ◽  
Topological Structure ◽  
Degrees Of Freedom ◽  
Dimensional Space ◽  
Principal Component ◽  
Biologically Inspired ◽  
Wing Kinematics ◽  
Wing Motion ◽  
Kinematic Synergies ◽  
Low Dimensional

In this article, we present methods to optimize the design and flight characteristics of a biologically inspired bat-like robot. In previous, work we have designed the topological structure for the wing kinematics of this robot; here we present methods to optimize the geometry of this structure, and to compute actuator trajectories such that its wingbeat pattern closely matches biological counterparts. Our approach is motivated by recent studies on biological bat flight that have shown that the salient aspects of wing motion can be accurately represented in a low-dimensional space. Although bats have over 40 degrees of freedom (DoFs), our robot possesses several biologically meaningful morphing specializations. We use principal component analysis (PCA) to characterize the two most dominant modes of biological bat flight kinematics, and we optimize our robot’s parametric kinematics to mimic these. The method yields a robot that is reduced from five degrees of actuation (DoAs) to just three, and that actively folds its wings within a wingbeat period. As a result of mimicking synergies, the robot produces an average net lift improvesment of 89% over the same robot when its wings cannot fold.

Strongly correlated transition metal oxides

2019 ◽  
Author(s):  
Ελένη Αζά
Keyword(s):  
Dielectric Permittivity ◽  
Single Crystal ◽  
Single Crystals ◽  
Long Range ◽  
Ground State ◽  
Degrees Of Freedom ◽  
Magnetic Order ◽  
Range Order ◽  
Long Range Order ◽  
Strongly Correlated

The discovery of materials with coexisting magnetic and ferroelectric orders, has revived theinterest of condensed matter physics and materials’ science communities maintaining the greatpromise of such fundamental mechanisms in devising applications ranging from portablemagnetoelectric (ME) sensors and memories to radar technologies. The present PhD thesis is a study in the field of strongly correlated systems where coupled properties arise from the interplay of charge and spin degrees of freedom over lattice topologies enabling competing magnetic interactions and therefore emergence of coupling of electric and magnetic order. Non-perovskite, two-dimensional (2D) Na-Mn-O oxides are revisited in scope of this in both polycrystalline and large single crystal forms. Among Na-deficient polymorphs, hexagonal α-Na0.7MnO2 (single crystals) has been investigated for the first time as a playground of competing interactions due to mixed Mnvalence (Mn4+ / Mn3+), fostered by Na vacancies in the structure. The competition of FM (Mn3+-Mn4+) and AFM (Mn3+ -Mn3+) interactions is believed to be the origin of the magnetic instability leading to a glassy ground state leaving also their footprint in the dielectric permittivity measurements. Competing FM and AFΜ interactions are also investigated as the origin of the anisotropic magnetic properties witnessed in a-NaxMnO2 (x= 0.96) single crystals. Neutron single crystal experiments show a well-established AFM long range order which vanishes above 26 K whilea coexistent canted antiferromagnetic state persists up to 45 K. In both alpha powders and aNa0.96MnO2 single crystals, the dielectric permittivity suggests the onset of the commensuratemagnetic long range order (T~ 45 K) which in the case of the powders allows a magnetocapacitance effect. Compositional modulations in β-NaMnO2, which are depicted as an intergrowth of α- and βlike oxygen coordinations, are found to trigger a proper-screw magnetic ground state which evolves into collinear commensurate AFM state. Features in the dielectric permittivity coincide with the onset of the commensurate AFM order giving away also the contribution of the α- structural domains. Further understanding of the mechanisms that dictate the relief of frustrated interactions and establishment of magnetic order together with the role of structural complexity in the form of domains or domain-walls is a direction that warrants further exploration as it will help us to resolve whether other coupled electron degrees of freedom are likely to be generated in this family of oxides.

Magnetic order in YbMn2Si2 — Neutron scattering investigation

2013 ◽  
Vol 63 (3) ◽  
pp. 314-319
Author(s):  
S. J. Campbell ◽  
M. Hofmann ◽  
R. A. Mole ◽  
K. Prokes ◽  
D. Wallacher ◽  
...  
Keyword(s):  
Neutron Scattering ◽  
Magnetic Order

scholarly journals Magnetic order in Nd2PdSi3 investigated using neutron scattering and muon spin relaxation

2019 ◽  
Vol 100 (13) ◽  
Author(s):  
M. Smidman ◽  
C. Ritter ◽  
D. T. Adroja ◽  
S. Rayaprol ◽  
T. Basu ◽  
...  
Keyword(s):  
Neutron Scattering ◽  
Spin Relaxation ◽  
Magnetic Order ◽  
Muon Spin ◽  
Muon Spin Relaxation

scholarly journals Nonequilibrium critical dynamics of low-dimensional frustrated magnets and multilayer structures

2019 ◽  
Vol 1163 ◽  
pp. 012068
Author(s):  
P V Prudnikovy ◽  
V V Prudnikov ◽  
V O Borzilov ◽  
M M Firstova ◽  
A A Samoshilova
Keyword(s):  
Multilayer Structures ◽  
Frustrated Magnets ◽  
Critical Dynamics ◽  
Low Dimensional

Spin Hall Effect Induced by Sound

2012 ◽  
Vol 190 ◽  
pp. 117-120
Author(s):  
I.I. Lyapilin
Keyword(s):  
Degrees Of Freedom ◽  
Spin Current ◽  
Coherent Motion ◽  
Spin Orbit Coupling ◽  
Spin Orbit ◽  
Spin Coherence ◽  
Nanoscale Systems ◽  
The Subject ◽  
Normal Current ◽  
Low Dimensional

Transport of electronic spins in low-dimensional and nanoscale systems is the subject of thenovel and quickly developing eld of spintronics. The possibility of coherent spin manipulationrepresents an ultimate goal of this eld. Typically, spin transport is strongly aected by couplingof spin and orbital degrees of freedom. The inuence of the spin orbit interaction is twofold.The momentum relaxation due to the scattering of carriers, inevitably leads to spin relaxationand destroys the spin coherence. On the other hand, the controlled orbital motion of carrierscan result in a coherent motion of their spins. Thus, the spin orbit coupling is envisaged as apossible tool for spin controling in electronic devices. In particular, it is possible to generatespin polarization and spin currents by applying electric eld, the phenomenon known as thespin-Hall eect (SHE) [1- 3]. The eect is manifested in the form of a spin current directedperpendicular to the normal current, which takes place in an electric eld.

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