Changes In Coercive Field Research Articles

Ferroelectric and dielectric properties of niobium-doped SrBi4Ti4O15 ceramics

An investigation of the ferroelectric and dielectric properties of niobium-doped SrBi4Ti4O15 (SrBi4−x/3Ti4−xNbxO15, x = 0.00, 0.003, 0.012, 0.03, 0.06) ceramics was presented. The ferroelectric property of SrBi4Ti4O15 was improved by niobium doping. The remanent polarization (2Pr) increases at first, then decreases with the increase in niobium content, while the coercive field changes little with Nb-doping. As the niobium content is 0.03, the 2Pr maximizes at a value of 24.7 µC cm−2, which is increased by about 60% in comparison with that of SrBi4Ti4O15. The Curie temperature of the samples hardly varies upon Nb-doping, which indicates that the good thermal stability of SrBi4Ti4O15 does not deteriorate after Nb addition.

90° domain wall relaxation and frequency dependence of the coercive field in the ferroelectric switching process

The mechanisms involved in the polarization switching process in soft and hard Pb(Zr53,Ti47)O3 (PZT) bulk ceramics were investigated through the dependency of the hysteresis loop on the frequency. In order to determine the influence of the defects on the domain switching dynamics, the samples were characterized in the virgin state and after a fatigue or a depinning process. The frequency dependence of the polarization revealed a strong relaxation of the 90° domain walls at ∼100 Hz. The results also revealed a strong influence of the kind of defect and their distribution in the ferroelectric matrix on the domain switching dynamics, which were reflected in the frequency dependence of the coercive field and the percentage of the backswitching. Initially, it was observed that the frequency dependence of the coercive field for the soft and the hard PZT in the virgin state had just one rate of change per decade in the entire frequency range investigated, which is the standard behavior found in the literature. However, after the fatigue or the depinning process, two rates of changes were noticed. Consequently, evidence of an upper-frequency limit for the coercive field changes was found. The percentage of the backswitching and its behavior for the soft PZT was almost independent of the fatigue state in the entire frequency range investigated. Nevertheless, for the hard PZT, an opposite behavior was verified. The reorientation of the domains was modeled as occurring in a viscous medium where several forces, such as viscous and restoring forces, act on them.

Patterned magnetic media from self-assembly template methods

Using lyotropic liquid crystalline phases and self-assembly from colloidal suspensions of polystyrene latex spheres, well-ordered, nanostructured templates were prepared. The results of electrochemical deposition of magnetic metals and alloys in the voids of these templates are presented. This technique has enabled the creation of magnetic nanostructures with 3D-achitectures on length scales 4 nm−1 μm. Changes in coercive field, by more than an order of magnitude were found, dominated by the effects of domain wall pinning. Clear transverse magnetisation suggests Bloch type of the domain walls. The in-plane component of the magnetic field drives the magnetic hysteresis. The templated electrodeposition technique offers the potential of a low-cost preparation method for sub-micron patterned magnetic media.

Magnetic antidot arrays from self-assembly template methods

Using self assembly from lyotropic liquid crystalline phases and from colloidal suspensions of polystyrene spheres templates, we have prepared well-ordered, nanostructured magnetic materials. We present the results of electrochemical deposition of magnetic metals and alloys in the interstitial space between these templates. This technique has enabled us to create magnetic nanostructures with three-dimensional achitectures on length scales of 4 nm–1 μm. We find changes in coercive field, by more than 1 order of magnitude, dominated by the effects of the nanoscale shapes. Varying the parameters in the preparation allows us to produce materials with predetermined magnetic parameters. The templated electrodeposition technique offers the potential of a low-cost preparation method for submicron patterned magnetic media.

Size-related ferroelectric-domain-structure transition in a polycrystalline PbTiO3 thin film.

We studied the size dependence of the ferroelectric domain structure in unique free-standing ${\mathrm{PbTiO}}_{3}$ thin film, composed of grains 60--1000 nm in size, with transmission-electron microscopy. With such samples, we showed that the apparent dependence of electrical properties on the thickness of polycrystalline thin films stems from their grain-size dependence. We found that a domain-structure transition, from predominantly multidomain to predominantly single domain occurs at a grain size of \ensuremath{\sim}150 nm (corresponding to a thickness 200--300 nm). Based on these experimental results, the drastic change of coercive field and dielectric permittivity below a thickness 200--300 nm was reasonably explained as resulting from a domain-structure transition. \textcopyright{} 1996 The American Physical Society.

Magnetostriction of thin films prepared from FeCuNbSiB alloy

Changes in coercive field, H c, and anisotropy field, H K, under a mechanical uniaxial stress in thin films of FeCuNbSiB alloy were measured. For the as-deposited films magnetoelastic coefficients of H c and H K were measured. Using for comparison Ni films as a standard we were able to determine the isotropic saturation magnetostriction constant, λ s = +27 × 10 −6.

Elastic stress-induced coercive field changes in Ni-Co-P films used in a rotating disk

The loss of recorded signal due to applied elastic stress on a NiCoP thin film recording material has been investigated by a new technique in which a uniform stress is applied by bending a sample in an applied demagnetizing field, and the change in total manetization of a uniformly magnetized sample is measured. The loss in magnetization is linear with the log of the number of bending cycles, for both convex and concave bending. Five cycles of bending under a stress of about 200 MPa reduces the coercive field of these films by several percent.

Gradual Increase of Coercive Field of X-Irradiated Rochelle Salt

The ageing of x-irradiated rochelle salt was studied through the change of coercive field at very low frequencies. The increase of coercive field just after x-irradiation was almost independent of frequency. This result can be explained if it is assumed that the radiation-induced-defects decrease the domain wall velocity through a certain interaction between the wall and the defects. The coercive field gradually increased at room temperature for 3 or more weeks after x-irradiation. This phenomenon should be closely related with the Okada's observation in which two dimensional thin cavities were seen on crystallographic basic planes when the x-irradiated crystal had been annealed at 40°C for about 3 hours.