Search results for "Ferroelectric"
showing 10 items of 374 documents
Magnetoelectric effect in mixed valency oxides mediated by charge carriers
2008
We show that the presence of free carriers in a substance can generate the multiferroic behavior. Namely, if the substance has mixed-valence ions, which can supply free carriers and have electric dipole and spin moments, all three types of long-range order (ferromagnetic, ferroelectric and magnetoelectric (ME)) can occur at low temperature. The physical origin of the effect is that charge carriers can mediate the multiferroic behavior via spin - spin (RKKY), dipole-dipole and dipole - spin interactions. Our estimate of the interaction magnitude shows that there exist an optimal carrier concentration, at which the strength of ME interaction is maximal and comparable to that of spin-spin RKKY…
Manifestation of dipole-induced disorder in self-assembly of ferroelectric and ferromagnetic nanocubes
2019
The authors thank Marjeta Maˇcek Kržmanc for many useful discussions. The financial support of M-ERA.NET Project Har-vEnPiez (Innovative nano-materials and architectures for integrated piezoelectric energy harvesting applications) is gratefully acknowledged. D.Z. acknowledges the support of the postdoctoral research program at the University of Latvia (Project No. 1.1.1.2/VIAA/1/16/072). The computing time of the LASC cluster was provided by the Institute of Solid State Physics (ISSP).
Domain-Enhanced Interlayer Coupling in Ferroelectric/Paraelectric Superlattices
2004
We investigate the ferroelectric phase transition and domain formation in a periodic superlattice consisting of alternate ferroelectric (FE) and paraelectric (PE) layers of nanometric thickness. We find that the polarization domains formed in the different FE layers can interact with each other via the PE layers. By coupling the electrostatic equations with those obtained by minimizing the Ginzburg-Landau functional we calculate the critical temperature of transition Tc as a function of the FE/PE superlattice wavelength and quantitatively explain the recent experimental observation of a thickness dependence of the ferroelectric transition temperature in KTaO3/KNbO3 strained-layer superlatti…
Quantum Mechanical Modelling of Pure and Defective KNbO3 Perovskites
2000
Ab initio electronic structure calculations using the density-functional theory (DFT) are performed for KNbO3 with and without defects. Ferroelectric distortive transitions involve very small changes in energies and are therefore sensitive to DFT-approximations. This is discussed by comparing results obtained with the local density approximation (LDA) to those where generalized gradient approximations (GGA) are used. The results of ab initio calculations for F-type centers and bound hole polarons are compared to those obtained by a semiempirical method of the Intermediate Neglect of the Differential Overlap (INDO), based on the HartreeFock formalism. Supercells with 40 and 320 atoms were us…
The Peculiar Physical Properties of Nanosized Ferroics (Nanoferroics)
2013
This Chapter contains the experimental facts about size effects in nanoferroics. They include ferroelectric, ferroelastic, magnetic and multiferroic nanostructured materials. The main peculiar feature of nanoferroics is the geometric confinement originating from their surfaces and interfaces. This is in contrast to the ordinary bulk ferroics, where the sample surface plays a minor role. In particular, in nanoferroics, the surface generates the physical properties gradients in the normal (to the surface) direction. This fact yields strong size effects and spatial inhomogeneity of the nanoferroics properties, which should be taken into account to get their adequate physical description. We re…
Multiferroic BiFeO<inf>3</inf> for conductance control at the LaAlO<inf>3</inf>/SrTiO<inf>3</inf>-interface
2015
Multiferroic materials possessing both magnetic and ferroelectric order enable in principle to switch order parameters using not the direct reciprocal field, e.g. to switch the magnetization by an electric field or the electric polarization by a magnetic field. A recent breakthrough was achieved by the demonstration of the ferromagnetic switching of a Co layer with an electric field employing the multiferroic BiFeO 3 [1]. The latter material is a perovskite based oxide that shows stable ferro-electricity as well as an antiferromagnetic order at room temperature [2,3]. Due to a Dzyaloshinskii-Moriya interaction induced by rotation of oxygen octahedra leading to noncollinear Fe-O-Fe bonds a s…
Polaronic relaxation in perovskites
1995
We report a low-temperature loss anomaly in several oxidic perovskites such as ${\mathrm{KTaO}}_{3}$, ${\mathrm{KTaO}}_{3}$:Nb, ${\mathrm{SrTiO}}_{3}$, ${\mathrm{SrTiO}}_{3}$:Ca, ${\mathrm{PbTiO}}_{3}$:La, Cu, and ${\mathrm{BaTiO}}_{3}$:La. We show that this anomaly arises from a low-frequency dielectric relaxation. The activation energy and the relaxation time of this process are nearly the same for all the investigated perovskites disregarding their composition, texture, and ferroelectric properties. We thus ascribe the loss anomaly to the localization of polarons on residual defects. Although the dielectric losses in ${\mathrm{SrTiO}}_{3}$ and ${\mathrm{SrTiO}}_{3}$:Ca are qualitatively …
Continuous theory of switching in geometrically confined ferroelectrics
2014
A theory of ferroelectric switching in geometrically confined samples like thin films and multilayers with domain structure has been proposed. For that we use Landau–Khalatnikov (LK) equations with free energy functional being dependent on polarization gradients. In this case, the consistent theory can be developed as for thin ferroelectric films and multilayers the domain structure reduces to Fourier series in ferroelectric polarization. The specific calculations are presented for thin film ferroelectric with dead layers and ferro-/paraelectric multilayer. Our theory is generalizable to ferroelectrics and multiferroics with other geometries.
Depolarization Field and Properties of Thin Ferroelectric Films with Inclusion of the Electrode Effect
2005
The influence of metallic electrodes on the properties of thin ferroelectric films is considered in the framework of the Ginzburg-Landau phenomenological theory. The contribution of the electrodes with different screening lengths l s of carriers in the electrode material is included in the free-energy functional. The critical temperature T cl , the critical thickness of the film, and the critical screening length of the electrode at which the ferroelectric phase transforms into the paraelectric phase are calculated. The Euler-Lagrange equation for the polarization P is solved by the direct variational method. The results demonstrate that the film properties can be calculated by minimizing t…
<title>Glass to ferroelectric phase transition induced by ac electric field in PbMg<formula><inf><roman>1/3</roman><…
2003
The nonlinear dielectric response of epitaxial heterostructures of relaxor ferroelectric PbMg1/3Nb2/3O3 thin films was experimentally studied using digital Fourier analysis. The amplitudes and the phase angles of the dielectric harmonics were determined as a function of temperature and the amplitude of the sinusoidal ac field. The response of the films was reconstructed assuming a linear contribution of the film-electrode interface capacitance. In the films at low amplitudes of ac field, a glass-like behavior was identified by a maximum in the third-order nonlinear dielectric permittivity around the freezing temperature, accompanied by a square field dependence of the amplitudes of the odd …