Stable Domain Configurations Research Articles

Excellent piezoelectric constant and thermal stability in BiScO3–PbTiO3 piezoelectric ceramics via domain engineering

The application of piezoelectric ceramics at high temperature is limited because they can't have both high piezoelectric coefficient and high Curie temperature. While, BiScO3–PbTiO3-based piezoelectric ceramics possessing high Curie temperature and piezoelectric properties simultaneously have drawn increasing attention due to their potential applications at high temperature. Here, we reported a novel compositional design of (1-x)[0.36BiScO3-0.64PbTiO3]-xBi(Sn1/3Nb2/3)O3 (abbreviated as BS-PT-xBSN). BS-PT-xBSN ceramic samples were synthesized by conventional solid state reaction method. According to the ternary phase diagram of BS-PT-xBSN ceramics brought up in this work, the morphotropic phase boundaries (MPB) were confirmed, which is located in the vicinity of x = 0.02. It canbe identified that the x = 0.02 sample near MPB has the optimal electric performance which are giant piezoelectric coefficient (d33 ∼ 450 pC/N, higher 18 % than undoped samples) and high Curie temperature (Tc ∼ 368 °C) as well as large remant polarization (Pr ∼ 46.6 μC/cm2). In addition, the variation of Pr is 3 % in the temperature range of 30–180 °C and the depolarization temperature of x = 0.02 ceramics is about 280 °C. Structural analysis such as in-situ PFM and TEM confirms that giant piezoelectricity and depolarization temperature are attributed to the appearance of nano-domain and complexity of domains as well as the stable domain configuration. This work not only reveal the high potential of BS-PT-xBSN for high-temperature piezoelectric applications but also open up a feasible approach to design new high-temperature piezoelectric ceramics.

Controllable conductive readout in self-assembled, topologically confined ferroelectric domain walls.

Charged domain walls in ferroelectrics exhibit a quasi-two-dimensional conduction path coupled to the surrounding polarization. They have been proposed for use as non-volatile memory with non-destructive operation and ultralow energy consumption. Yet the evolution of domain walls during polarization switching makes it challenging to control their location and conductance precisely, a prerequisite for controlled read-write schemes and for integration in scalable memory devices. Here, we explore and reversibly switch the polarization of square BiFeO3 nanoislands in a self-assembled array. Each island confines cross-shaped, charged domain walls in a centre-type domain. Electrostatic and geometric boundary conditions induce two stable domain configurations: centre-convergent and centre-divergent. We switch the polarization deterministically back and forth between these two states, which alters the domain wall conductance by three orders of magnitude, while the position of the domain wall remains static because of its confinement within the BiFeO3 islands.

Control of stable magnetization states in permalloy nanorings using magnetic nanowires

We study the evolution of the magnetic field-induced switching between the stable domain configurations of permalloy nanoring structures, when magnetic nano-wires are attached to them. Magnetoresistance measurements were performed on such devices for two configurations of the attached nano-wires: (i) when they are at diametrically opposite ends of the nanoring, and (ii) when the nanowires are at an obtuse angle with respect to each other. During the measurements, the direction of application of the in-plane magnetic field is varied to understand the switching properties of the devices. Micromagnetic simulations were carried out in order to understand the domain configuration and reversal mechanism. We show that due to the nature of domain walls created by the presence of the nano-wires in the obtuse configuration, a vortex state can be stabilized in the nano-ring. We extended our studies to various nanoring devices with different widths while keeping a constant thickness.

Effect of lithographically-induced strain relaxation on the magnetic domain configuration in microfabricated epitaxially grown Fe81Ga19

We investigate the role of lithographically-induced strain relaxation in a micron-scaled device fabricated from epitaxial thin films of the magnetostrictive alloy Fe81Ga19. The strain relaxation due to lithographic patterning induces a magnetic anisotropy that competes with the magnetocrystalline and shape induced anisotropies to play a crucial role in stabilising a flux-closing domain pattern. We use magnetic imaging, micromagnetic calculations and linear elastic modelling to investigate a region close to the edges of an etched structure. This highly-strained edge region has a significant influence on the magnetic domain configuration due to an induced magnetic anisotropy resulting from the inverse magnetostriction effect. We investigate the competition between the strain-induced and shape-induced anisotropy energies, and the resultant stable domain configurations, as the width of the bar is reduced to the nanoscale range. Understanding this behaviour will be important when designing hybrid magneto-electric spintronic devices based on highly magnetostrictive materials.

Closed-circuit domain quadruplets in BaTiO3nanorods embedded in a SrTiO3film

Cylindrical BaTiO${}_{3}$ nanorods embedded in $\ensuremath{\langle}100\ensuremath{\rangle}$-oriented SrTiO${}_{3}$ epitaxial film in a brushlike configuration are investigated in the framework of the Ginzburg-Landau-Devonshire model. It is shown that strain compatibility at BaTiO${}_{3}$/SrTiO${}_{3}$ interfaces keeps BaTiO${}_{3}$ nanorods in the rhombohedral phase even at room temperature. Depolarization field at the BaTiO${}_{3}$/SrTiO${}_{3}$ interfaces is reduced by an emission of the 109${}^{\ensuremath{\circ}}$ or 71${}^{\ensuremath{\circ}}$ domain boundaries. In case of 10--80-nm diameter nanorods, the ferroelectric domains are found to form a quadruplet with a robust flux-closure arrangement of the in-plane components of the spontaneous polarization. The out-of-plane components of the polarization are either balanced or oriented up or down along the nanorod axis. Switching of the out-of-plane polarization with coercive field of about $5\ifmmode\times\else\texttimes\fi{}{10}^{6}$ V/m occurs as a collapse of a 71${}^{\ensuremath{\circ}}$ cylindrical domain boundary formed at the curved circumference surface of the nanorod. The remnant domain quadruplet configuration is chiral, with the ${C}_{4}$ macroscopic symmetry. More complex stable domain configurations with coexisting clockwise and anticlockwise quadruplets contain interesting arrangement of strongly curved 71${}^{\ensuremath{\circ}}$ boundaries.

Equilibrium configurations and phase transitions in dipole lattices

Two-dimensional square and hexagonal lattices of magnetic dipoles with the number of rows 1–4 have been studied. Based on the numerical analysis, equilibrium stable domain configurations, including the minimum number of lattice dipoles, have been revealed; the conditions for the creation and destruction of domains have been determined; and their associated changes in the magnetic moment of the lattice and in the energy of the dipole interaction have been found. The conditions for the occurrence of phase transitions that change the configuration of the lattices have been investigated and the conditions for unidirectional propagation of the front of the phase transition have been established. A comparative analysis of different square and hexagonal lattices has been performed in terms of the specific features of the formed domains and the observed orientation phase transitions.

Pressure dependence of piezoelectric properties of aPb(Mg1/3Nb2/3)O3–PbTiO3 binary system single crystal near a morphotropic phase boundary

The piezoelectric properties of aPb[(Mg1/3Nb2/3)0.68]Ti0.32O3 binary system single crystal poled along the [001] direction in therhombohedral phase were investigated under pressures up to 400 MPa at25 °C. For the transverse electromechanical property, the differenceΔf between the resonancefr and antiresonancefrequencies fa, the Δf/fr and the electromechanical coupling coefficientk31 value in thek31 mode withhydrostatic pressure (p) became smaller because of the increase infr and the almostconstant fa with p. The k31 value decreased by 16% at 400 MPa. On the other hand, for the longitudinal electromechanical property,the Δf, theΔf/fr and thek33 valuein the k33 mode with p remained almost constant because of the almost constantfr and fa with p. The changes in the values of the elastic compliancess11E ands33E withp were found to be largefrom the changes in fr and fa with p. s11E ands33E at 400 MPa wereestimated to be 35.4 and 75.1 × 10−12 m2 N−1, respectively. A mechanical quality factorQ almost constantwith p in thek33 mode in contrast tothe large decrease in Q in the k31 mode with p in the pressure range up to 200 MPa was observed. Ak33 value almostconstant with p is considered, on the basis of the engineered domain concept, to bedue to the stable domain configuration responsible for the longitudinalk33 mode. Furthermore, the superior piezoelectric properties of the rhombohedral [001]single crystal in the vicinity of the morphotropic phase boundary compositionwere recently pointed out to come from the large shear piezoelectric constantd15 of their single domain property. The hydrostatic pressure cannot influence thepiezoelectric properties from the viewpoint of the contribution of the large shear moded15, since the uniform pressure introduces no shearing stresses. Consequently, thek33 value measured forthe k33 mode remainedalmost constant with p in the measured pressure range.

Pressure Dependence of Piezoelectric Properties of Pb(Zn1/3Nb2/3)O3-PbTiO3 Binary System Single Crystal near a Morphotropic Phase Boundary

The piezoelectric properties of a Pb[(Zn1/3Nb2/3)0.91]Ti0.09O3 binary system single crystal oriented along the [001] direction in the rhombohedral phase was investigated under pressures up to 500 MPa at 25°C. With increasing hydrostatic pressure, the change of the resonance and antiresonance frequency characteristic curves of the impedance and phase from sharp to broad ones was observed. The resonance frequency fr increased, while the antiresonance frequency fa remained almost constant. The electromechanical coupling coefficient in the k31 mode decreased markedly with pressure, and the value of the k31 mode decreased by 18% at 500 MPa. The electromechanical coupling coefficient in the k33 mode decreased slightly with pressure. The value of the k33 mode decreased slightly by only 3% at 500 MPa. The large decrease in the k31 value with pressure exhibited a marked contrast with the slight decrease in the k33 value with pressure. The changes in the values of the elastic compliances s11E and s33E with pressure were observed to be large from the changes in fr and fa with pressure. s11E and s33E at 400 MPa were estimated to be 7.23 and 13.95×10-11 m2/N, respectively. The large k31 in the k31 mode is considered to be due to the mechanical softness of the PZN-PT(91/9) single crystal. On the other hand, the slight decrease in k33 with pressure is thought, on the basis of the engineered domain concept, to be due to the stable domain configuration responsible for the longitudinal k33 mode.

Simulation of boundary condition influence in a second-order ferroelectric phase transition

Using a two-dimensional Ginzburg–Landau model and the finite-element computational method, we have calculated stable domain configurations resulting from a second-order ferroelectric phase transition for a finite-sized system. The boundary conditions applied here correspond to fully charge compensated situations, either by surface electrodes or by the injection of charges (or defects) near the sample surface. The domain wall thickness of a finite system without surface electrodes was found to become thinner as it approaches sample surfaces. This is distinctively different from that of an infinite system for which a planar wall assumption can be used. The orientation of the macroscopic polarization of a finite system without surface electrodes was found to be determined by its aspect ratio. A size effect was observed when all the dimensions were reduced simultaneously. The relaxation process in the formation of domains and the switching process have also been simulated for charge neutral boundary conditions using a time dependent Ginzburg–Landau model. The simulation results verified that the surfaces are the favored nucleation sites for domain switching.

Crystallographically engineered BaTiO3 single crystals for high-performance piezoelectrics

Dielectric and piezoelectric properties of BaTiO3 single crystals polarized along the 〈001〉 crystallographic axes were investigated as a function of temperature and dc bias. Electromechanical coupling (k33)∼85% and piezoelectric coefficients (d33)∼500 pC/N, better or comparable to those of lead-based Pb(Zr, Ti)O3 (PZT), were found from 〈001〉-oriented orthorhombic crystals at 0 °C, as a result of crystallographic engineering. A rhombohedral BaTiO3 crystal polarized along 〈001〉 also exhibited enhanced piezoelectric performance, i.e., k33∼79% and d33∼400 pC/N at −90 °C, superior to PZTs at the same temperature. It was found that the crystal structure determined the (in)stability of the engineered domain state in BaTiO3 single crystals. Rhombohedral (3m) crystals at −100 °C exhibited a stable domain configuration, whereas depoling occurred in crystals in the adjacent orthorhombic phase upon removal of the E field.

Magnetic properties of submicron Co islands and their use as artificial pinning centers

We report on the magnetic properties of elongated submicron magnetic islands and their influence on a superconducting film. The magnetic properties were studied by magnetization hysteresis loop measurements and scanning-force microscopy. In the as-grown state, the islands have a magnetic structure consisting of two antiparallel domains. This stable domain configuration has been directly visualized as a 2x2-checkerboard pattern by magnetic-force microscopy. In the remanent state, after magnetic saturation along the easy axis, all islands have a single-domain structure with the magnetic moment oriented along the magnetizing field direction. Periodic lattices of these Co islands act as efficient artificial pinning arrays for the flux lines in a superconducting Pb film deposited on top of the Co islands. The influence of the magnetic state of the dots on their pinning efficiency is investigated in these films, before and after the Co dots are magnetized.

E-field dependence of piezoelectric properties of rhombohedral PZN-PT single crystal

The E-field dependence of piezoelectric properties of rhombohedral single crystal PZN-4.5%PT were investigated as a function of crystallographic orientation. For <111> oriented crystals, crystal partial depoling and subsequent domain reorientation results in a peak in dij vs. E-field curves at −5kV/cm, followed by nonhysteretic dij saturation. This behavior indicates that crystal became single domain at E>30kV/cm. Low field values for dij's of single domain crystals were calculated by extrapolating these high field values. Hydrostatic piezoelectric coefficient dh ∼ 55pC/N, calculated for the single domain crystal, also could be measured in the hydrostatic chamber. In contrast to <111> poled crystals, stable domain configurations of <001> oriented crystals were the origin of consistent dij values regardless of the measurement technique. Piezoelectric coefficients, d33 −2280pC/N and d31 as high as −1000 pC/N were reproducibly measured. Although dh=d33+2d31 is relevant to the related symmetry, calculated dh ∼ 300pC/N could not be obtained from the response under hydrostatic pressure (dh − 50pC/N). This discrepancy is discussed in relation to the domain state and crystal symmetry.

Large magnetic anisotropy in single crystal us

It is shown for ferromagnetic US that an extremely large anisotropy restrains magnetic moments to 〈111〉 easy axes, resulting in a near cos θ angular dependence of the magnetization away from the 〈111〉 axes. This is further confirmed by torque measurements, which in addition show large hysteresis effects upon rotation through the hard axes. It is illustrated through torque and magnetization measurements that a near stable domain configuration can be established by field rotation through decreasing angular amplitude around a hard 〈001〉 direction. The anisotropy constant K 1( T) is estimated by computing the small angle through which the magnetization deviates from the 〈111〉 axes when a field is applied along the [001] direction.