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We attempt to modify the magnetoelectric properties of antiferromagnetic Bi2Fe4O9 nanograins by substituting multivalent Mn ions at Fe sites. The doped Bi2Fe4O9 nanograins are synthesized by a hydrothermal method with a different Mn content x (x is the mole ratio of Mn to Mn plus Fe; x = 0.00, 0.02, 0.04, 0.06, and 0.10). Among them, the x = 0.04 sample shows the anomalous decrease of lattice parameters a and b, the lowest antiferromagnetic transition temperature, and the largest saturated magnetization. Besides, the magneto-dielectric effect (Δɛ/ɛ ∼ −4.9%) and the magneto-striction constant (λ ∼ −1.1 × 10−4) of the x = 0.04 sample are also the largest compared with others (220 K and 0.6 T). Combined with Raman scattering and x-ray photoelectron measurement, it is considered that the substitution site of Mn ions varies with an increase of doping amount x, which also leads to the change of valence state of Mn ions and the lattice structure, and further affects the strength of magnetic interaction and spin-lattice coupling. [ABSTRACT FROM AUTHOR]

SnO2:Cu memristor devices were fabricated to investigate the influence of Frenkel defects on endurance behavior. We controlled the oxygen pressure during pulsed laser deposition to obtain different Frenkel defect conditions. For SnO2:Cu devices with homogeneous Frenkel defects, high-resistance state (HRS) fatigue was observed with increasing switching cycles due to the reduction of interfacial barriers caused by unrecoverable fragments of conductive filaments. In bilayer SnO2:Cu devices with Frenkel defect concentration gradients, the vertical Fick force resulting from the concentration gradient can drive mobile oxygen ions to restrain the formation of unrecoverable fragments. Thus, HRS fatigue was improved by restraining the reduction of interfacial barriers. When the gradient becomes large, the bilayer devices demonstrate HRS rise and stuck switching in several switching cycles. In this case, the Fick force may dominate the diffusion of mobile oxygen ions, leading to the overfilling of oxygen vacancies at the interface and an increase in interfacial barriers. [ABSTRACT FROM AUTHOR]

To explore the novel thin film with multiferroicity at room temperature, the bismuth-layer-structured Bi5Fe0.5Co0.5Ti3O15 (BFCT) thin films were prepared using chemical solution deposition technique. The microstructure, electric, and magnetic properties were investigated in BFCT film. A defined hysteresis loop of the BFCT film was obtained with the remnant polarization (2Pr) ∼ 31.7 μC/cm2 at 1 kHz under the electric field 300 kV/cm. To exclude contribution of the leakage current to polarization, we studied the dependence of hysteresis loops on the measuring frequency in the range from 100 Hz to 2 kHz and made the positive-up-negative-down (PUND) measurements in BFCT thin film. Both the results indicate the intrinsic ferroelectric property, and the leakage current does not play a big role in BFCT film. Meanwhile, the &eh;-V curve can also support the natural ferroelectricity in the BFCT film. We also found that the BFCT film shows weak ferromagnetism with the saturated magnetization (Ms) ∼2.6 emu/cm3. Furthermore, the magneto-dielectric effect was observed with MDC ∼ 0.39% at the frequency 100 kHz. The origin of weak ferromagnetism and the magneto-dielectric effect was discussed. [ABSTRACT FROM AUTHOR]

Yb3Fe5O12 ceramics with garnet structure were prepared employing the solid-state reaction method. The results reveal that the emergence of Fe2+ ions greatly affects dielectric relaxation, magnetic relaxation, saturation magnetization, and magnetoelectric coupling, which was further confirmed by oxygen treatment. More interestingly, the magnetoelectric coefficient (α) reaches 28 ps m-1 at room temperature, which is among the largest values for present single-phase magnetoelectric materials. [ABSTRACT FROM AUTHOR]

In order to match the high-density requirement of ferroelectric memories, ferroelectric Bi3.15Nd0.85Ti3O12 nanotubes with outer diameter of about 100 nm and wall thickness of about 30 nm were synthesized using a sol-gel method. Transmission electron microscope images and Raman spectra revealed the Bi-layered perovskite structure of these nanotubes. Their dielectric constant and remnant polarization were comparable with those of thin film form. Piezoelectric hysteresis loops of individual nanotube measured by piezoresponse force microscope indicate their asymmetry, and the switched nanotubes show long term retention. [ABSTRACT FROM AUTHOR]

Imprint behavior of polycrystalline Bi3.25La0.75Ti3O12 thin films under stress was studied. The voltage shift along the positive voltage axis can be depressed by tensile stress while increased by compressive stress. With the measured voltage increasing, the voltage shift referred above increases and the increase trend gets enhanced under both compressive and tensile stress compared with that at zero stress. The asymmetric distribution of the trapped charged in films, which is caused by the increase of the in-plane polarization component for the domain reorientation induced by stress or for the voltage-assisted domain walls depinning, was considered the contribution to the voltage shift. [ABSTRACT FROM AUTHOR]

SrZrO3 (SZO) thin films were deposited on (111) Pt/Ti/SiO2/Si substrates via metal organic decomposition method at different temperatures in flowing oxygen or nitrogen atmospheres. The microstructures of the films were characterized by x-ray diffraction. The dielectric properties and the leakage characteristics were investigated as well. The results showed that nitrogen ambient was helpful for the SZO films to crystallize into perovskite phase with polycrystalline structure. Meanwhile, the electric properties varying with annealing conditions were discussed in detail. [ABSTRACT FROM AUTHOR]

The dependence of the magnetoelectric coefficients (αE) in the Terfenol-D/Tb2(MoO4)3 bilayer composite on the magnetic bias fields and the frequencies has been studied. The strain with butterfly loop of Tb2(MoO4)3 under an external magnetic field was observed and the effect of ferroelasticity of the Tb2(MoO4)3 on the magnetoelectric coupling was discussed. More than one peak of αE as function of frequency of ac magnetic field were observed and it implies existence of bending resonance mode besides the longitudinal resonance mode in the bilayer composite. [ABSTRACT FROM AUTHOR]

Mechanical stress effect on aging behavior of Bi3.25La0.75Ti3O12 (BLT) and PbZr0.53Ti0.47O3 (PZT) films was investigated. It is found that the remnant polarization decreases with time while the coercive field increases in stress-free BLT films. For unconfined PZT films, both the remnant polarization and the coercive field decrease as time elapses. The applied tensile stress weakens the aging of remnant polarization of BLT films but strengthens the aging of coercive field, while the applied tensile stress possesses opposite effect. In contrary, the applied compressive stress simultaneously improves the aging behavior of both remnant polarization and coercive field of PZT films. Mechanical-stress-induced variation of domain wall mobility in different materials was suggested as the possible origin of these observations. This work indicates that the aging behavior modification using stress could be realized, and it is helpful for promoting the reliability of ferroelectric films for industrial applications. [ABSTRACT FROM AUTHOR]

Pr-doped SrTiO3 ceramics were fabricated by the conventional solid-state reaction method. Pr-doping greatly decreased the lattice parameters and the average grain size of SrTiO3 ceramics sample. Two thermally activated dielectric relaxations were found for the low- and high-temperature relaxations, respectively. By means of a detailed analysis, the low-temperature relaxation was ascribed to the electric hopping between Pr3+ and Pr4+ induced by the Pr-doping, and the origin of the high-temperature relaxation was changed from oxygen vacancies to the polar nanoregions with the increase of Pr content. [ABSTRACT FROM AUTHOR]