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We have comparatively studied the dielectric, ferroelectric, conduction, and photovoltaic properties of Ti/BaTiO3 (BTO)/SrRuO3 (SRO) and Pt/BTO/SRO capacitors. The resistive switching (RS) is observed in the Pt/BTO/SRO capacitor while it is absent in the Ti/BTO/SRO capacitor, which may be attributed to the interfacial layer existing between Pt and BTO and the Ti/BTO Ohmic interface, respectively. Further analyses on the conduction mechanisms suggest that the RS may be caused by the opening/closing of conduction paths in the Pt/BTO interfacial layer, whereas the polarization is ruled out as the origin of RS because of the inconsistency between the RS switching voltages and coercive voltages. On the other hand, it is observed that the photovoltaic effects (PVEs) in both Ti/BTO/SRO and Pt/BTO/SRO capacitors are electrically unswitchable and the open-circuit voltages of the two capacitors are similar in magnitude, implying that the PVE is driven by an internal bias field rather than the polarization-induced field. The existence of such an internal bias field is indicated by the self-polarization and imprint phenomena. Our study demonstrates that the interfacial layer and the internal bias field can be the major causes for the RS and PVE in certain ferroelectric capacitors, respectively, whereas the polarization may not necessarily play a role. [ABSTRACT FROM AUTHOR]

In this study, controllable morphology evolution of hexagonal strontium ferrite (SrFe12O19) micro/nano-crystals has been demonstrated. Single phase strontium ferrite platelets with hexagonal morphology were successfully prepared by conventional ceramic process. In the hexagonal crystals, it is revealed that the anisotropic growth rate is changed, with the increasing of ball milling time, from relatively high rate along the <001> direction (c-axis) to direction, leading to the morphology evolution. Moreover, the optimal saturation magnetization (MS) is 69.5 emu/g, which is intensely close to the theoretical value (72 emu/g). This study provides the direct evidence of the enhanced reaction activity induced by high energy ball milling in strontium hexaferrite platelets and the obtained SrFe12O19 particles are promising for the hard magnet application and the magnetoelectric electronics. [ABSTRACT FROM AUTHOR]

We investigate how epitaxial strain affects the conductivity and charge transport of Ba0.6La0.4TiO3 (BLTO) films deposited by pulsed laser deposition. Depositing BLTO films with thicknesses varying from 14.1 to 95.9 nm gives differing epitaxial strains, with a maximum strain up to ~6% for the thinnest film of 14.1 nm. Transport measurements demonstrate that film thickness (i.e. epitaxial strain) affects the conductivity, carrier mobility, and concentration. Measurements of resistivity versus temperature demonstrate that all the BLTO films undergo a distinct semiconductor-metal phase transition, and the transition temperature TSM also depends clearly on strain. For all the films, the charge transport follows the small-polaron hopping mechanism below TSM and the thermal phonon scattering mechanism above TSM. These results prove that strain in epitaxial films strongly affects the conductivity and charge transport of traditional insulating ferroelectric oxide films. [ABSTRACT FROM AUTHOR]

La-doped BaTiO3 thin films (BLTO) were deposited by pulsed laser deposition, and a comprehensive investigation on their conductivity, charge transport, and ferroelectricity was carried out. Resistivity-temperature (T) measurements demonstrate that the conductivity of Ba1−xLaxTiO3 (x  =  0.05, 0.1, 0.2, 0.3, and 0.4) films can be largely regulated in a wide range. The BLTO film exhibits typical semiconductor conduction behavior for x  ⩽  0.3, whereas a typical metallic conduction behavior was observed for x  =  0.4 at T  >  240 K. The La doping concentration x also plays an important role on the charge transport mechanisms. For x  ⩽  0.3, the charge transport follows small-polaron hopping at low temperature (T  <  300 K) and thermal excitation at high temperature (T  ⩾  300 K). While the charge transport for x  =  0.4 changes from small-polaron hopping to thermal phonon scattering with the increase of temperature. Piezo-force microscopy measurements reveal that BLTO films exhibit ferroelectricity for La doping concentration x up to 0.4. These results demonstrated that La doping plays an important role in regulating the conductivity and charge transport in BLTO films. More importantly, we revealed experimentally that macro metallic conduction and ferroelectricity can coexist in the La-doped BaTiO3 epitaxial thin films. [ABSTRACT FROM AUTHOR]

Magnetic skyrmions in multilayer stack structures are promising magnetic memory bits for applications in race-track storage devices or random-access memories. For practical implementation in energy efficient memory devices, it is essential to achieve a deterministic switch of skyrmion states, e.g. nucleation and elimination, triggered by electric fields. In this work, by means of micromagnetic simulation, we demonstrate the strain-mediated electric field driven switching of magnetic skyrmion and other topological states without the presence of a magnetic field in a proposed device consisting of nanodiscs of trilayer Pt/Co/Ta stacks on a piezoelectric substrate. It is revealed that the multiple magnetic state switching behaviors, including the nucleation and elimination of skyrmion or labyrinth stripe domain states, as well as topological transitions between skyrmion, vortex, skyrmionium and vertical single domain states, can be triggered by applying an external electric field mediated by strains. The corresponding critical strains and their dependence on the geometric parameters of the nanodiscs (e.g. size and number of stacks) for triggering such magnetic switching are also explored. The stability of these topological domain states and possible switching behaviors (e.g. volatile and non-volatile) between the different states are discussed as well. The capability for controlled switching of these topological states provides a new pathway to energy efficient high-density magnetoelectric memory and logic devices. [ABSTRACT FROM AUTHOR]

The ferroelectric properties of 20 nm Hf0.5Zr0.5O2 (HZO) thin films has been investigated in a wide temperature range from 100 K to 450 K. The remnant polarization of HZO thin films decreases slightly from 24.6 μC cm−2 (100 K) to 17.9 μC cm−2 (450 K), indicating a robust temperature stability. The capacitors also exhibit excellent endurance properties up to 109 cycles at 100 K and 300 K, and their endurance cycles slightly degrades to 108 at an elevated temperature of 450 K. The results show that HZO ferroelectric thin films have great potential for future emerging memory applications in various harsh temperature environments. [ABSTRACT FROM AUTHOR]

Efficient and cost-competitive fabrication of high-quality ferroelectric and multiferroic nanostructures is of general interest. In this work, a top-down nano-patterning technique is developed by the Ar+ ion beam etching in combination with the sacrificed ultrathin anodic alumina (AAO) mask. This technique is demonstrated by preparation of the epitaxial BiFeO3 (BFO) nanostructures of various geometries, including nanodot and anti-nanodot arrays. The lateral dot size is as small as ∼60 nm and an ultrahigh dot density of ∼60 Gbit/inch2 is achieved. It is revealed that the etching process involves sequential shape evolution of both the AAO mask and the underlying BFO film, resulting in the nanodots and anti-nanodots arrays of various geometries. The as-etched BFO nanodots array exhibits well-established ferroelectric domain structures and reversible polarization switching, as examined by piezoresponse force microscopy (PFM). It is suggested that this technique is extendable to fabrication of a wide range of functional oxide nanostructures for potential nanoelectronic applications. [ABSTRACT FROM AUTHOR]