Ferroelectric polarization in multiferroics

2019 ◽  
Vol 4 (9) ◽  
Author(s):  
Stephan Krohns ◽  
Peter Lunkenheimer
Keyword(s):  
Electric Field ◽  
Strong Coupling ◽  
Degrees Of Freedom ◽  
Ferroelectric Properties ◽  
Charge Order ◽  
Electric Polarization ◽  
Ferroelectric Polarization ◽  
Past Century ◽  
Type I ◽  
Solid State Physics

Abstract Multiferroic materials, showing ordering of both electrical and magnetic degrees of freedom, are promising candidates enabling the design of novel electronic devices. Various mechanisms ranging from geometrically or spin-driven improper ferroelectricity via lone-pairs, charge-order or -transfer support multiferroicity in single-phase or composite compounds. The search for materials showing these effects constitutes one of the most important research fields in solid-state physics during the last years, but scientific interest even traces back to the middle of the past century. Especially, a potentially strong coupling between spin and electric dipoles captured the interest to control via an electric field the magnetization or via a magnetic field the electric polarization. This would imply a promising route for novel electronics. Here, we provide a review about the dielectric and ferroelectric properties of various multiferroic systems ranging from type I multiferroics, in which magnetic and ferroelectric order develop almost independently of each other, to type II multiferroics, which exhibit strong coupling of magnetic and ferroelectric ordering. We thoroughly discuss the dielectric signatures of the ferroelectric polarization for BiFeO3, Fe3O4, DyMnO3 and an organic charge-transfer salt as well as show electric-field poling studies for the hexagonal manganites and a spin-spiral system LiCuVO4.

scholarly journals Avoiding gauge ambiguities in cavity quantum electrodynamics

2021 ◽  
Vol 11 (1) ◽  
Author(s):  
Dominic M. Rouse ◽  
Brendon W. Lovett ◽  
Erik M. Gauger ◽  
Niclas Westerberg
Keyword(s):  
Electric Field ◽  
Strong Coupling ◽  
Electromagnetic Fields ◽  
Quantum Electrodynamics ◽  
Degrees Of Freedom ◽  
Cavity Quantum Electrodynamics ◽  
Strong Coupling Regime ◽  
Energy Eigenstates ◽  
Gauge Choice ◽  
Gauge Ambiguity

AbstractSystems of interacting charges and fields are ubiquitous in physics. Recently, it has been shown that Hamiltonians derived using different gauges can yield different physical results when matter degrees of freedom are truncated to a few low-lying energy eigenstates. This effect is particularly prominent in the ultra-strong coupling regime. Such ambiguities arise because transformations reshuffle the partition between light and matter degrees of freedom and so level truncation is a gauge dependent approximation. To avoid this gauge ambiguity, we redefine the electromagnetic fields in terms of potentials for which the resulting canonical momenta and Hamiltonian are explicitly unchanged by the gauge choice of this theory. Instead the light/matter partition is assigned by the intuitive choice of separating an electric field between displacement and polarisation contributions. This approach is an attractive choice in typical cavity quantum electrodynamics situations.

Theory of Spin-charge-orbital States in the Frustrated System RFe2O4

2006 ◽  
Vol 966 ◽  
Author(s):  
Sumio Ishihara ◽  
Makoto Naka ◽  
Aya Nagano
Keyword(s):  
Monte Carlo Simulation ◽  
Low Temperatures ◽  
Degrees Of Freedom ◽  
Magnetic Ordering ◽  
Charge Order ◽  
Electric Polarization ◽  
Effective Hamiltonian ◽  
Orbital State ◽  
Orbital Degree ◽  
Magnetic Ordering Temperature

ABSTRACTElectronic structure in multiferroic compound RFe2O4. is studied theoretically. We suggest that orbital degree of freedom in a Fe2+ ion is active. The effective Hamiltonian for spin, charge and orbital degrees of freedom is derived. Numerical analyses with the multi-canonical Monte-Carlo simulation show that the electric polarization is attributed to the charge order with momentum (1/3, 1/3). A magnitude of the polarization is enhanced around the magnetic ordering temperature due to the coupling between spin and charge. Conventional orbital order is not expected from the numerical calculation. We discuss possible orbital state at low temperatures.

Effect of chromium substitution on the dielectric, ferroelectric and piezoelectric properties of PLNZNT ceramics (P=Pb2+, L=La3+, N=Nd3+, Z=Zr4+, N=Nb5+, T=Ti4+)

2021 ◽  
pp. 345-352
Author(s):  
Sadok. Hadjadj ◽  
Afaf. Bouchaala ◽  
Noura. Mebrouki ◽  
Lazhar. Benmabrouk ◽  
Ahmed. Boutarfaia
Keyword(s):  
Electric Field ◽  
Piezoelectric Properties ◽  
Ferroelectric Properties ◽  
Electric Polarization ◽  
Chromium Concentration ◽  
Tetragonal Symmetry ◽  
Hysteresis Cycle ◽  
Scanning Electron Micrographs ◽  
Average Grain Size ◽  
Ferroelectric And Piezoelectric Properties

Piezoelectricity is one of the renewable and clean electrical energy sources, as it is generated from materials specially manufactured for this purpose in proportions and scales called piezoelectric materials, that is, electricity resulting from mechanical work that produces the electric field, and this is known as the direct piezoelectric effect. An inverse mechanical effect can also be observed when an electric field is applied to the same piezoelectric material that deforms and returns to its original shape after the electric field is removed. In order to contribute to improving the properties of these materials that have been prepared from insulating ceramic materials having an equivalent formula: Pb0.975 La0.015 Nd0.01 [(Zr 0,524 Ti 0,476) 0.9875 -3/4 z Nb0.005 Crz]O3 abbreviated PLNZCNT (z = 0%, 0.5%, 0.75%, 1%, 1.25%, 1,5% and 2%). The formation of pure single-phase perovskite compounds of tetragonal symmetry for all samples was confirmed by X-ray diffraction (XRD) analyzes. The scanning electron micrographs show that the grains have melted, most of the separating walls have disappeared, and the average grain size has increased. Information about the effects of chromium concentration on the measured properties was obtained based on temperature and frequency measurements of the dielectric properties of PLNZNT ceramics, represented by an increase in Curie temperature with increasing Cr3+ concentration. The ferroelectric properties of materials are characterized by the presence of a polarization hysteresis cycle as a function of the applied electric field (P-E). To measure the piezoelectric and electromechanical properties at room temperature, was used by the standard resonance and anti-resonance method. It was found that the sample E2 (0.75%) sintered at 1200°C achieves excellent dielectric, ferroelectric and piezoelectric properties (𝜺r=24394.51, tan δ =0.072 and Tc = 378K). The values of saturated electric polarization (Ps=29.61 µC/cm²), remnant electric polarization (Pr=24.63 µC/cm²) and coercive electric field (Ec=0.905kV/mm), as well as piezoelectric charge coefficient (d33 = 435 pC/N) for sample E2 (0.75%).

Spontaneous electric polarization and electric field gradient in hybrid improper ferroelectrics: insights and correlations

2021 ◽  
Author(s):  
Samuel Silva dos Santos ◽  
Michel L. Marcondes ◽  
Ivan P. Miranda ◽  
Pedro Rocha-Rodrigues ◽  
Lucy Vitória Credidio Assali ◽  
...  
Keyword(s):  
Electric Field ◽  
Electric Field Gradient ◽  
Ab Initio ◽  
Field Gradient ◽  
Electric Polarization ◽  
Double Perovskites

An ab-initio study for several hybrid improper ferroelectric (HIF) materials in the Ruddlesden-Popper phases and double perovskites structures is here presented. The focus is on the correlation between the electric...

A polycrystal hysteresis model for ferroelectric ceramics

2006 ◽  
Vol 462 (2069) ◽  
pp. 1573-1592 ◽  
Author(s):  
Y Su ◽  
G.J Weng
Keyword(s):  
Electric Field ◽  
Hysteresis Loop ◽  
Ferroelectric Properties ◽  
Electric Displacement ◽  
Hysteresis Loops ◽  
Ferroelectric Ceramics ◽  
Domain Growth ◽  
Thermodynamic Approach ◽  
Hysteresis Model ◽  
Self Consistent

Most key elements of ferroelectric properties are defined through the hysteresis loops. For a ferroelectric ceramic, its loop is contributed collectively by its constituent grains, each having its own hysteresis loop when the ceramic polycrystal is under a cyclic electric field. In this paper, we propose a polycrystal hysteresis model so that the hysteresis loop of a ceramic can be calculated from the loops of its constituent grains. In this model a micromechanics-based thermodynamic approach is developed to determine the hysteresis behaviour of the constituent grains, and a self-consistent scheme is introduced to translate these behaviours to the polycrystal level. This theory differs from the classical phenomenological ones in that it is a micromechanics-based thermodynamic approach and it can provide the evolution of new domain concentration among the constituent grains. It also differs from some recent micromechanics studies in its secant form of self-consistent formulation and in its application of irreversible thermodynamics to derive the kinetic equation of domain growth. To put this two-level micromechanics theory in perspective, it is applied to a ceramic PLZT 8/65/35, to calculate its hysteresis loop between the electric displacement and the electric field ( D versus E ), and the butterfly-shaped longitudinal strain versus the electric field relation ( ϵ versus E ). The calculated results are found to be in good quantitative agreement with the test data. The corresponding evolution of new domain concentration c 1 and the individual hysteresis loops of several selected grains—along with those of the overall polycrystal—are also illustrated.

scholarly journals Large linear magnetoelectric effect and field-induced ferromagnetism and ferroelectricity in DyCrO4

2019 ◽  
Vol 11 (1) ◽  
Author(s):  
Xudong Shen ◽  
Long Zhou ◽  
Yisheng Chai ◽  
Yan Wu ◽  
Zhehong Liu ◽  
...  
Keyword(s):  
Magnetic Field ◽  
Electric Field ◽  
Spin Structure ◽  
Magnetoelectric Effect ◽  
Electric Polarization ◽  
Metamagnetic Transition ◽  
Ferromagnetic Component ◽  
Antiferromagnetic Structure ◽  
Field Control ◽  
Ferromagnetic Magnetization

Abstract All the magnetoelectric properties of scheelite-type DyCrO4 are characterized by temperature- and field-dependent magnetization, specific heat, permittivity, electric polarization, and neutron diffraction measurements. Upon application of a magnetic field within ±3 T, the nonpolar collinear antiferromagnetic structure leads to a large linear magnetoelectric effect with a considerable coupling coefficient. An applied electric field can induce the converse linear magnetoelectric effect, realizing magnetic field control of ferroelectricity and electric field control of magnetism. Furthermore, a higher magnetic field (>3 T) can cause a metamagnetic transition from the initially collinear antiferromagnetic structure to a canted structure, generating a large ferromagnetic magnetization up to 7.0 μB f.u.−1. Moreover, the new spin structure can break the space inversion symmetry, yielding ferroelectric polarization, which leads to coupling of ferromagnetism and ferroelectricity with a large ferromagnetic component.

Partial Dissolution of Charge Order Phase Observed in -(BEDT-TTF)2PF6 Single Crystal Field Effect Transistor

2016 ◽  
Vol 16 (4) ◽  
pp. 3267-3272
Author(s):  
Masatoshi Sakai ◽  
Norifumi Moritoshi ◽  
Shigekazu Kuniyoshi ◽  
Hiroshi Yamauchi ◽  
Kazuhiro Kudo ◽  
...  
Keyword(s):  
Electric Field ◽  
Single Crystal ◽  
Temperature Dependence ◽  
Crystal Field ◽  
Field Effect ◽  
Field Effect Transistor ◽  
Electrical Conductance ◽  
Charge Order ◽  
Crystal Field Effect ◽  
Effect Transistor

The effect of an applied gate electric field on the charge-order phase in β-(BEDT-TTF)2PF6 single-crystal field-effect transistor structure was observed at around room temperature by technical improvement with respect to sample preparation and electrical measurements. A relatively slight but systematic increase of the electrical conductance induced by the applied gate electric field and its temperature dependence was observed at around the metal-insulator transition temperature (TMI). The temperature dependence of the modulated electrical conductance demonstrated that TMI was shifted toward the lower side by application of a gate electric field, which corresponds to partial dissolution of the charge-order phase. The thickness of the partially dissolved charge order region was estimated to be several score times larger than the charge accumulation region.

Effective Locality QCD calculations and the Gribov copy problem

2020 ◽  
Vol 35 (27) ◽  
pp. 2050230 ◽  
Author(s):  
T. Grandou ◽  
R. Hofmann
Keyword(s):  
Gauge Field ◽  
Strong Coupling ◽  
Degrees Of Freedom ◽  
Green's Functions ◽  
Green’S Functions ◽  
Strong Coupling Limit ◽  
Unexpected Result ◽  
Remarkable Property ◽  
Gauge Invariant

Standard functional manipulations have been proven to imply a remarkable property satisfied by the fermionic Green’s functions of QCD and dubbed effective locality. Resulting from a full gauge invariant summation of the gauge field degrees of freedom, effective locality is a non-perturbative property of QCD. This unexpected result has lead to suspect that the famous Gribov copy problem had been somewhat overlooked. It is argued that it is not so. The analysis is conducted in the strong coupling limit, relevant to the Gribov problem.

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