Magnetism manipulation in ferromagnetic/ferroelectric heterostructures by electric field induced strain

Magnetization manipulation by an electric field(E-field) in ferromagnetic/ferroelectric heterostructures has attracted increasing attention because of the potential applications in novel magnetoelectric devices and spintronic devices, due to the ultra-low power consumption of the process. In this review, we summarize the recent progress in E-field controlled magnetism in ferromagnetic/ferroelectric heterostructures with an emphasis on strain-mediated converse magnetoelectric coupling. Firstly, we briefly review the history, the underlying theory of the magnetoelectric coupling mechanism, and the current status of research. Secondly, we illustrate the competitive energy relationship and volatile magnetization switching under an E-field. We then discuss E-field modified ferroelastic domain states and recent progress in non-volatile manipulation of magnetic properties. Finally, we present the pure E-field controlled 180° in-plane magnetization reversal and both E-field and current modified 180° perpendicular magnetization reversal.     

Distribution and amplification of an electric field in ferroelectric-dye heterostructures

The distribution of an electric field has been investigated in Langmuir-Blodgett thin-film heterostructures prepared by sequentially transferring layers of the ferroelectric copolymer poly(vinylidene fluoride-trifluoroethylene) P(70% VDF 70% ?C30% TrFE) and the azo dye. An alternating-current voltage applied to the electrodes is unevenly distributed across layers of the dye and the copolymer in accordance with a constant induction along the normal to the heterostructure. The electric-field-induced shift of the absorption spectrum of the dye serves as a probe of the electric field and reveals a noticeable amplification of the electric field in the dye layers (by a factor of 2?C7). The electric field in the ferroelectric is directed opposite to the direction of the electric field applied to the electrodes of the heterostructure.     

The exact solutions of Kane equations which have position-dependence band gap in an external non-uniform electric field

The energy spectrum of electrons in narrow band gap semiconductor nanocrystals which have position dependence band gap in an external non-uniform electric field which compensate the position dependence of the band edge of the valence band potential are studied theoretically taking into account the non-parabolicity of electrons in dispersion laws. The exact solutions of the Kane equations with strong spin–orbital interaction are determined with and without magnetic field via the band gap changes as a function of the position. The position dependence of the band gap is taken parabolically.     

Strong amplification of an electric field and electro-optical response in ultrathin heterostructures ferroelectric-linear dielectric

An electroded heterostructure consisting of a dye layer sandwiched between two polymer ferroelectric layers is discussed. The dye layer plays a role of the probe of the electric field measured by an electroabsorption technique. Using this new method the electric field in ferroelectric and dielectric layers can be measured separately. When an a.c. voltage is applied to the heterostructure, the electric field in the dye layer increases 2.2 times (up to 0.55 GV/m), whereas the field in the ferroelectric decreases 2 times with respect to the average field in the entire structure. Moreover, the dye layer sandwiched between the ferroelectric layers may stand without breakdown the fields 5–7 times higher than a neat reference dye layer confined between metal electrodes. Therefore, the performance of electro-optical, electromechanical and other field controlled devices may be improved considerably when their functional materials are placed between ferroelectrics layers.     

Phase diagram of water under an applied electric field

Simulations are used to investigate for the first time the anisotropy of the dielectric response and the effects of an applied electric field E(ex) on the phase diagram of water. In the presence of electric fields ice II disappears from the phase diagram. When E(ex) is applied in the direction perpendicular to the ac crystallographic plane the melting temperatures of ices III and V increase whereas that of ice Ih is hardly affected. Ice III also disappears as a stable phase when E(ex) is applied in the direction perpendicular to the ab plane. E(ex) increases by a small amount the critical temperature and reduces slightly the temperature of the maximum density of liquid water. The presence E(ex) modifies all phase transitions of water but its effect on solid-solid and solid-fluid transitions seems to be more important and different depending on the direction of E(ex).     

Lasing characteristics of a pendant drop deformed by an applied electric field

The lasing properties of an oval-shaped resonant cavity (ORC) with a continuously variable aspect ratio have been studied. The ORC was formed with a dye-doped pendant drop placed inside a variable static electric field. When the drop ORC was pumped by a nitrogen laser, lasing from the ORC was found to have strong directional emission characteristics and an intensity enhancement factor as great as 19.5. Calculated results of light rays escaping from ORC's by refraction are in good agreement with the experimental data.     

Synthesis and photonic band gap characterization of high quality photonic crystal heterostructures

High quality photonic crystal heterostructures with a thin titania planar defect layer between its two constitutional photonic crystals were fabricated and their structural and optical properties were analyzed. The results suggest that the thin planar defect layer is beneficial to separate the two constitutional photonic crystals from each other and to reduce the roughness of the interface. The quality of the resulting photonic crystal heterostructures is improved largely and the main features of the photonic band gaps of the two constitutional photonic crystals are inherited. The predominant optical quality of these heterostructures (e.g. deep double photonic band gaps and steep photonic band edges) may afford new flexibility and functionality for engineered photonic behavior in practical devices such as late-model light-operated switches.     

Emission of terahertz radiation from GaAsN/GaAs heterostructures in an electric field

Emission of terahertz radiation from strained Be-doped GaAsN layers has been revealed at 4.2 K in postbreakdown electric fields. Heavy and light hole subbands are split in strained layers, and, along with localized acceptor states, resonant states arise. The spectrum of terahertz radiation has been obtained, the current-voltage characteristics of the samples were investigated, and the energy spectra of acceptors were calculated. Peaks in the spontaneous emission spectrum correlate well with the results of the energy spectrum calculations. The transitions between the resonant and localized states of the acceptors make the main contribution to the terahertz radiation intensity.     

Tunable magnetic interaction by an applied electric field in a Co-adsorbed SiC monolayer

The magnetic properties of Co-adsorbed SiC monolayer under an external electric field are investigated using first-principles method. In the absence of the electric field, the interaction between two Co atoms is ferromagnetic, which is originated by the p?d hybridization between Co and its neighboring C and Si atoms. When an electric field was introduced along the c axis, the interaction between two Co dopants switched from ferromagnetic to antiferromagnetic, which could be dominated by the competition between p?d exchange and superexchange. Moreover, the magnetic anisotropy prefers to parallel to the a axis and it seems not to be turn into the c axis under the electric field.     

Pair production in an electric field applied for a short time

An expression is obtained for the probability of pair production in a homogeneous electric field applied for a short time and a constant inhomogeneous magnetic field when both fields have the same direction. The dependence of the probability is investigated for short and long times of application of the electric field.     

Experimental study of influence of external electric field on the photonic band gap of chiral liquid crystals

Influence of an external electric field on the boundaries of photonic band gap of a chiral liquid crystal has been studied experimentally. It is shown that by using a negative chiral liquid crystal and homeotropic boundary conditions one can increase the abruptness of photonic band gap boundaries and control thus the band gap width by application of the external electric field.     

Fe–Ag granular multilayers and heterostructures studied in applied magnetic field

An (0.2 nm ⁵⁷Fe / 2.6 nm Ag)₇₅ granular multilayer sample and heterostructures with additional continuous Fe layers in different sequences were studied in magnetic field applied at different temperatures. The broadening of the superparamagnetic lines was found to be very similar for the three samples in applied fields both parallel and perpendicular to the sample plane. While the layer sequence has no significant effect on the superparamagnetic properties, the continuous magnetic layers follow a different approach to saturation in perpendicular magnetic fields.     

Asymmetric quantum dots in an applied electric field: discontinuous electron density

We consider non-interacting electrons in asymmetric quantum dots with either hard wall boundary conditions (rectangular quantum dots) or anharmonic confinement (elliptic quantum dots). In both cases, due to finite size effects, a homogeneous electric field applied along the long axis is shown to induce abrupt changes in the electron density, parallel and perpendicular to the field direction. Making use of this property, we propose a pure electrical mechanism to control the magnitude of the effective exchange interaction between two weakly-coupled quantum dots. This kind of system has been proposed recently as possible realization of quantum gates for quantum computation.     

Diffraction behavior of an azo-dye-doped nematic liquid crystal without applied electric field

We investigate the dependence of the two-beam coupling diffraction efficiency on the experimental parameters, and hence achieve the optimum experimental conditions for holographic recording in planar Methyl Red-doped nematic liquid crystal film without external electric field. Under the optimum experimental conditions, the diffraction efficiency of a holographic grating is improved to 21.4%, and holographic image with long-term stability is stored in the film. These results provide an experimental basis for holographic data storage in this liquid crystal film.     

Dynamic behaviors of ferroelectric liquid crystal molecules under an applied electric field

The dynamic changes in ferroelectric liquid crystal (FLC) molecular alignments under an applied electric field are examined by observing the formation of conoscopic figures with a time resolution of 0.1 ms. Close agreements between observed and simulated conoscopic figures under low voltage (30 V) were obtained. Under high voltage (120 V), however, the observed conoscopic figures became blurred between 0.8 ms and 1.1 ms after reversal of the electric field. The light scattering producing the blurriness occurred due to the development of fast transient molecular alignments during the switching transition above the applied voltage 70 V.