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(Na0.5Bi0.5)TiO3 (NBT)-based materials have been widely studied for their large electric-field-induced strains. However, a high coercive field ( Ec) has long hindered the applications of NBT-based materials. Here, we propose a simple method to significantly reduce the Ec of rhombohedral NBT-based crystals through domain engineering. By applying an alternating current (AC) electric field along the [001] direction, the Ec of Mn-doped (Na0.485K0.015Bi0.5)TiO3 single crystal can be reduced from 70 to 20 kV/cm after about 25 cycles without sacrificing the ferroelectric polarization. Meanwhile, the piezoelectric coefficient d33 and the optical transparency of the crystals are also enhanced compared with those after direct-current electric field poling. The domain structure characterization shows that the AC cycles can form a laminar domain configuration, in which the 109° domain walls are parallel to (001) planes. It is demonstrated that in the laminar domain configuration, almost only 71° polarization switching occurs when the external electric field is reversed. The required energy for polarization reversal is significantly lower than that of the “4R” domain configuration; thus, the Ec is reduced greatly. The low Ec is maintained after depolarization at 250 °C, evidencing good thermal stability of the laminar domain configuration. Furthermore, this method is also applicable to other rhombohedral single crystals and may be applied to [001]-textured polycrystalline ceramics in the future; thus, it may indeed benefit the practical applications of NBT-based piezoelectric devices.

A significant enhancement of the Jc in magnetic field in the Ag‐clad Bi‐Pb‐Sr‐Ca‐Cu‐O (BPSCCO) wires has been achieved by using a short period melt processing. The weak links have been largely eliminated in the melt‐processed tapes which exhibits a 3–10‐fold increase in the Jc at 77 K and 1 T over the normally processed tapes. For tapes with a thickness 80 μm 60% of melt‐processed samples have the Jc values between 10 000 and 27 000 A/cm2 at 77 K in zero field. The irreversibility lines determined using ac susceptibility measurements under dc fields confirmed the improvement of flux pinning in the melt‐processed tapes compared with the normally processed tapes. The improved Jc‐H characteristics may be attributed to the desirable microstructures produced from the high Tc phase formation‐decomposition‐recovery process through the use of a short period melting.

We present careful experiments on the multiferroicity in Ca3CoMn0.92O6 by Fe substitution of Mn. It is revealed that a proper Fe substitution modulates the Co/Mn spin order, favoring the ferroelectricity. The multifold interactions between the intra-chain spins and inter-chain spins are analyzed. It is suggested that the Mn deficiency and Fe substitution can break the inter-chain interactions to some extent, resulting in the delicate competition between these mutual interactions. The modulation of the ionic (charge) disorder and spin frustration order is the core physics for improving the ferroelectric performance.

The dielectric and ferroelectric behaviors of Zn2+-doped SrTiO3 (STO-Zn) have been investigated to explore the effects of Zn-doping on quantum fluctuations and ferroelectric instability. Structurally, the smaller Zn2+ ions occupy the Sr2+ sites at low substitution level up to 0.9% and an over-substitution may lead to impurity phase. It is found that no ferroelectric or relaxor-like anomaly emerges, while significantly enhanced dielectric constant and broad dielectric plateau are identified upon the substitution. These phenomena observed in Zn2+-doped STO are slightly different from well investigated Ca2+-doped STO and additional mechanism besides the off-centrality of Zn2+ ions at Sr2+ sites is possible. The transverse-field Ising model is consulted to explain self-consistently the observed effects. (C) 2012 American Institute of Physics. [http://dx.doi.org/10.1063/1.3703070]

We present careful experiments on the spin order and multiferroicity of Mn-deficient Ca3CoMn1−xO6 with respect to the Co/Mn compensated Ca3Co1+yMn1−yO6. It is revealed that a slight destruction of the Co/Mn ionic order does not damage but significantly enhances the ferroelectricity in terms of the transition point and polarization magnitude, due to the Mn-deficiency enhanced degree of Co/Mn spin ordering in comparison with Ca3Co1+yMn1−yO6. The delicate competition between the ionic (charge) order and spin frustration is the core physics for improving the ferroelectric performance.

J.W., Y.L., R.L.W., Q.L., and Y.P.G. appreciate the support of the Australian Research Council (ARC) in the form of a Discovery Grant. Y.L. also appreciates support from the ARC Future Fellowships program.

A direct inter-conversion between conduction electron spin-current and spin wave spin-current has been experimentally realized in Pt/Y3Fe5O12 and Pt/Y3Fe5O12/Pt heterostructures [Y. Kajiwara et al., Nature 464, 262 (2010)]. We investigate the dynamics of this inter-conversion in an in-plane spiral magnet with the nearest-neighboring interaction and Dzyaloshinskii-Moriya interaction, using the modified Landau-Lifshitz-Gilbert equation. The calculations indicate that an unattenuated conical spin wave in the spiral magnet can be excited by a spin-torque representing a conduction-electron spin-current. The substantial role of the Dzyaloshinskii-Moriya interaction in stabilizing such unattentuated spin wave transmission is revealed. In addition, the influences of the spin-torque term and damping coefficient on the stability of the spin wave transmission are discussed.

We perform Monte Carlo simulation of the ferroelectricity induced by spiral spin order in spin-1/2 LiCu2O2 based on the Mostovoy phenomenological theory. The simulated spiral spin order parameter and ferroelectric polarization, respectively, as a function of temperature and magnetic field are compared with recent experiments. The substantial differences in several aspects of the multiferroicity between the simulation and experiments allow a reasonable argument that the spiral spin order may not be the unique origin for the ferroelectricity generation.

Pb(Zr0.4Ti0.6)O3 thin films with a thickness of 500nm were spin coated on (110) preferred Pt bottom electrodes using a sol-gel method, in which the (110) preferred Pt bottom electrode was developed by using a (100)-oriented conductive oxide electrode LaNiO3 film as an adhesion layer on a SiO2∕Si substrate. X-ray diffraction analysis and field emission scanning electron microscopy show that the as-grown Pb(Zr0.4Ti0.6)O3 films are highly (110)-oriented with a columnar structure. It indicates that the (110) preferred Pt bottom electrode is effective for growing highly (110)-oriented Pb(Zr0.4Ti0.6)O3 films. The as-grown Pb(Zr0.4Ti0.6)O3 films show excellent dielectric and ferroelectric properties with dielectric constant e33T∕e0=1620, loss tangent tanδ=2.1%, spontaneous polarization 2Ps=158μC∕cm2, and remnant polarization 2Pr=92μC∕cm2. Excellent pyroelectric properties are also detected in the (110)-oriented films. At room temperature, the pyroelectric coefficient and the figure of merit for detectivity can r...