Polarization screening in polymer ferroelectric films: Uncommon bulk mechanism

Charge compensation at the interface is a fundamental phenomenon determining the operation conditions of thin-film devices incorporating ferroelectrics. The underlying mechanisms have been thoroughly addressed in perovskite ferroelectrics where the charge compensation originates from injection through the interface-adjacent layer. Here, we demonstrate that polarization screening in the polymer ferroelectric polyvinylidene fluoride-trifluoroethylene (P(VDF-TrFE)) films can be dominated by charge injection through the bulk, unlike ferroelectric oxides. The experimental evidence relies on polarization imprint under applied field and time-dependence of the dielectric constant. A linearized electrostatic model correctly accounts for the observed trends and links their occurrence to the unique properties of P(VDF-TrFE). (C) 2012 American Institute of Physics. [http://dx.doi.org/10.1063/1.4754146

Nonvolatile ferroelectric control of ferromagnetism in (Ga,Mn)As

There is currently much interest in materials and structures that provide coupled ferroelectric and ferromagnetic responses, with a long-term goal of developing new memories and spintronic logic elements. Within the field there is a focus on composites coupled by magnetostrictive and piezoelectric strain transmitted across ferromagnetic-ferroelectric interfaces, but substrate clamping limits the response in the supported multilayer configuration favoured for devices. This constraint is avoided in a ferroelectric-ferromagnetic bilayer in which the magnetic response is modulated by the electric field of the poled ferroelectric. Here, we report the realization of such a device using a diluted magnetic semiconductor (DMS) channel and a polymer ferroelectric gate. Polarization reversal of the gate by a single voltage pulse results in a persistent modulation of the Curie temperature as large as 5%. The device demonstrates direct and quantitatively understood electric-fieldmediated coupling in a multiferroic bilayer and may provide new routes to nanostructured DMS materials and devices via ferroelectric domain nanopatterning. The successful implementation of a polymer-ferroelectric gate fieldeffect transistor (FeFET) with a DMS channel adds a new functionality to semiconductor spintronics and may be of importance for future low-voltage spintronics devices and memory structures.Comment: 19 pages, 5 figure

Non-volatile ferroelectric gating of magnetotransport anisotropy in (Ga,Mn)(As,P)

We demonstrate charge-mediated and non-volatile control of anisotropic magnetoresistance (AMR) in a dilute magnetic semiconductor (Ga,Mn)(As, P) with an integrated polymer ferroelectric gate. The persistent electric field associated with switchable polarization in the ferroelectric layer is shown to be capable of strongly modulating the AMR magnitude. Furthermore, ferroelectric gate switching has a profound impact on the nature of AMR, changing the symmetry of the effect and enhancing/suppressing the crystalline component of AMR. Thus, in addition to a rather weak modulation of the ferromagnetic Curie temperature (4-5 K) reported previously, the ferroelectric gate can induce a strong deterministic switching of the magnetotransport anisotropy. (C) 2012 American Institute of Physics. [http://dx.doi.org/10.1063/1.4731245

Magnetic domain wall propagation under ferroelectric control

Control of magnetic domain walls (DWs) and their propagation is among the most promising development directions for future information-storage devices. The well-established tools for such manipulation are the spin-torque transfer from electrical currents and strain. The focus of this paper is an alternative concept based on the nonvolatile ferroelectric field effect on DWs in a ferromagnet with carrier-mediated exchange coupling. The integrated ferromagnet/ferroelectric structure yields two superimposed ferroic patterns strongly coupled by an electric field. Using this coupling, we demonstrate an easy-to-form, stable, nondestructive, and electrically rewritable switch on magnetic domain wall propagation. DOI: 10.1103/PhysRevB.86.23513

Physical origin of conduction in PZT thin films

Leakage conduction of Pt-Pb(ZrXTi:(1-X))O-3-Pt capacitors is studied by means of different measuring techniques and analyzed in terms of semiconductor properties of the system. Based on the experimental data, it is concluded that two different regimes of carrier injection (with the critical electric field of the crossover between these regimes being independent of the measuring technique) are responsible for true leakage conduction in Pt-Pb(ZrXTi1-X)O-3-Pt films. For interpretation of the experimental results a Space-Charge-Influenced-Injection model which takes into account both role of charge of depletion in the bulk of the film and injection through the blocking contact is proposed. This model describes well the main features of the observed current-voltage characteristics and provides a reasonable fit for the current-voltage curves measured at elevated temperatures, the values of the fitting parameters being in a good agreement with the results of other studies. The presented study provides insight in me physical nature of leakage conduction of Pt-Pb(ZrXTi1-X)O-3-Pt system and suggests a method for analyzing its semiconductor parameters by means of conduction measurements