Study Of Domain Wall Motion Research Articles

Enhanced ferroelectric properties of P(VDF-TrFE) thin films from Nb nanopin electrodes

We demonstrate the influence of Nb nanopin electrodes on ferroelectric properties of poly(vinylidene fluoride-ran-trifluoroethylene) (P(VDF-TrFE)) thin films deposited using a spin-coating technique. The Nb nanopin electrodes consisting of an array of regular hexagon nanopins were formed by virtue of a multiple anodizing process and an etching process of an Al/Nb/SiO2/Si multilayer structure. An electric field enhancement of the Nb nanopin electrodes contributed to the improved ferroelectric polarizations, low coercive electric fields, and fast switching characteristics of the P(VDF-TrFE) thin-film capacitors. Futhermore, the Nb nanopin electrodes made a significant contribution to low activation energy of domain wall motion. In particular, the study of domain wall motion by piezoresponse force microscopy support that the fast switching properties of the P(VDF-TrFE) capacitors is attributed to the low activation energy for the domain wall motion. This work provides a solution to solve problems of the high coercive and switching electric fields that have been considered obstacles in electronic devices and applications of the P(VDF-TrFE) thin films.

The effect of cooling rate on structural and electrical properties of multiferroic BLF‐PT ceramics

AbstractThe solid solutions of 0.57(Bi0.8La0.2)FeO3‐0.43PbTiO3 (BLF‐PT) were prepared by the solid‐state reaction process. The as‐sintered ceramics were annealed at 350°C and then cooled in different media. BLF‐PT ceramics cooled in boiling water (BW) and NaCl solutions exhibit the rhombohedral structure with higher domain density, while the tetragonal structure was observed in the specimen cooled in the furnace. Moreover, BLF‐PT ceramics cooled in BW with cooling rate of about 10°C/s exhibit the enhanced electrical properties with dielectric constant εr, remnant polarization Pr, piezoelectric constant d33 of 940, 28 μC/cm2 and 210 pC/N, respectively. Rayleigh analysis was utilized to study of domain wall motion of BLF‐PT ceramics cooled in different media.

Experimental study of domain wall motion in long nanostrips under the influence of a transverse field

We report the real time study of field driven domain wall (DW) motion in giant magnetoresistance nanostrips under the influence of both longitudinal and transverse fields. We have found clear evidence that transverse fields influence the DW dynamics below and above the Walker field [N. L. Schryer and L. R. Walker, J. Appl. Phys. 45, 5406 (1974)] drastically. We show the suppression of the Walker breakdown process and a huge enhancement in DW velocity below the Walker field. The maximum velocity reported here is 4500 m/s.

The influence of thermal activation and the intrinsic temperature dependence of the spin torque effect in current-induced domain wall motion

An experimental study of domain wall motion in Ni80Fe20 ring structures induced by current pulses as well as conventional magnetic fields is presented. Using constrictions we demonstrate that current-induced domain wall motion can be used to displace walls into parts of the structure where no pulsed currents are flowing. Measurements at variable temperatures between 2 and 300 K show that the fields necessary for wall motion decrease with increasing temperature, which can be explained by thermal activation. For the current-induced case we find, depending on the geometry and temperature range, that the current densities necessary for displacement can increase or decrease with rising temperature. This indicates that, in addition to thermal excitations, an intrinsic temperature dependence of the efficiency of the spin torque effect is present and leads to an increase in the critical current density with increasing temperature.

Nanoscale studies of domain wall motion in epitaxial ferroelectric thin films

Atomic force microscopy was used to investigate ferroelectric switching and nanoscale domain dynamics in epitaxial Pb(Zr0.2Ti0.8)O3 thin films. Measurements of the writing time dependence of domain size reveal a two-step process in which nucleation is followed by radial domain growth. During this growth, the domain wall velocity exhibits a v∝exp−(1∕E)μ dependence on the electric field, characteristic of a creep process. The domain wall motion was analyzed both in the context of stochastic nucleation in a periodic potential as well as the canonical creep motion of an elastic manifold in a disorder potential. The dimensionality of the films suggests that disorder is at the origin of the observed domain wall creep. To investigate the effects of changing the disorder in the films, defects were introduced during crystal growth (a-axis inclusions) or by heavy ion irradiation, producing films with planar or columnar defects, respectively. The presence of these defects was found to significantly decrease the creep exponent μ, from 0.62–0.69 to 0.38–0.5 in the irradiated films and 0.19–0.31 in the films containing a-axis inclusions.

Temperature Dependence of the Spin Torque Effect in Current-Induced Domain Wall Motion

We present an experimental study of domain wall motion induced by current pulses as well as by conventional magnetic fields at temperatures between 2 and 300 K in a 110 nm wide and 34 nm thick Ni80Fe20 ring. We observe that, in contrast with field-induced domain wall motion, which is a thermally activated process, the critical current density for current-induced domain wall motion increases with increasing temperature, which implies a reduction of the spin torque efficiency. The effect of Joule heating due to the current pulses is measured and taken into account to obtain critical fields and current densities at constant sample temperatures. This allows for a comparison of our results with theory.

Studies of domain wall motion. III. The field dependence of differential susceptibility at the early stage of magnetization

For pt.II see ibid., vol.3, p.4783 (1991). Differential susceptibilities chi diff of nickel wire, Permalloy-42 wire, 4% silicon iron sheet and bars of SAE 1015 and 1045 steels were measured when undergoing uniform magnetic field sweeping. The field dependences of chi diff of wires, sheet and bars at the early stage of magnetization were studied: in general, chi diff decreases with increasing sweep rate of field and the chi diff-H relationship depends on sample shape. The experimental results are interpreted using a phenomenological model based on domain wall (DW) motion that it is modest generalization of the Rayleigh law at low field. This model is also compared with a previous model of magnetomechanical damping.

Studies of domain wall motion. I. Internal friction under magnetization

The internal friction (IF) measurement technique is used to study the magnetization of pure iron, nickel and Permalloy-42. The IF of samples undergoing a uniform magnetic field sweep is measured with a torsion pendulum. An IF peak is observed in the field range 0-10 Oe. The field sweeping increases the IF and hence the characteristic quantity is the difference between the IF measured in field sweeping and that in a static field, which is called dynamic internal friction. The dynamic IF shows a viscoelastic feature; it increases with increasing H/ omega where H is the field sweep rate and omega the angular frequency of the alternating strain. The behaviour of the dynamic IF shows that it is caused by the domain wall motion in field sweeping and thus is related to a magnetomechanical interaction.

Applications of the pyroelectric probe technique to the study of domain wall motion in ferroelectric NaNO2and TGS

Abstract The Miller-Savage law is verified for low intensity electric fields and the power law for high fields, in the case of thick samples. For very thin crystal plates (e < 10 μm), the Miller-Savage law must be replaced by an exponential law. In all cases the different parameters can be kept constant in a small range of thickness by using an “effective electric field.”

Perspectives in magnetics: Italy

A review is given of fundamental research in magnetics pursued in Italian universities and laboratories of Consiglio Nazionale delle Ricerche. The main topics covered are in the field of soft materials, hard materials and garnets. The electronic structure of metals is investigated by polarized neutron diffraction, while studies of domain wall motion provide the basis for fully understanding power loss processes and mechanisms. Work on amorphous magnetism has focused in particular on the study of short range order in these materials. Most fundamental research on hard materials is directed toward permanent magnet applications, microwave devices and magnetic recording. Magnetization processes are a major subject of investigation in these materials, with applications both to hexagonal ferrites and rare earth-3d metal compounds. The crystal chemistry of garnets is being pursued by carrying out a variety of metal substitutions and studying site occupancies and valence states in both bulk materials and LPE films. The static and dynamic properties of domains are also investigated for display and memory applications in addition to microwave properties and materials.

Study of domain wall motion by Barkhausen method

Abstract Applying Barkhausen effect, changes in the activation energy of domain wall motion in ferroelectric ageing are studied for TGS crystals grown in paraelectric phase. Barkhausen pulse field distributions are reported for Cu2+ doped TGS crystals (6.8 · 10−2 and 10−4 wt% in the crystal) and related with defect-induced changes in domain structure and wall clamping.

Structures of Ferroelectric Domains in Triglycine Sulfate

Domain structures in ferroelectric glycine sulfate are studied by etching in various alcohols. Methyl alcohol etches the head of polarization more readily than the tail end, and gives, in a relatively short time, clear domain patterns. Moreover, this etchant etches the (001) surface very slowly and after a long time delineates the arranging manner of domains along the polarization axis. Domain boundaries have cylindrical surfaces parallel to b axis, but the sections perpendicular to the axis are quite indefinite in dimensition and direction. Domain terminated with a rounded tip in the antiparallell domain was observed. Crystal imperfection seems to have a considsrable effect on the domain structure of this crystal. Some preliminary studies of domain wall motion under the application of electric field are also reported.