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Searching for low-power-consuming and high-efficient methods for well controllable driving of skyrmion motion is one of the most concerned issues for future spintronic applications, raising high concern with an appreciated choice of magnetic media and driving scenario. In this work, we propose a novel scenario of spin wave driven skyrmion motion in a ferrimagnetic (FiM) lattice with the net angular momentum {\delta}s. We investigate theoretically the effect of both {\delta}s and the circular polarization of spin wave on the skyrmion dynamics. It is revealed that the momentum onto the skyrmion imposed by the excited spin wave can be partitioned into a ferromagnetic term plus an antiferromagnetic term. The ratio of these two terms and consequently the Hall angle of skyrmion motion can be formulated as the functions of {\delta}s, demonstrating the key role of {\delta}s as an effective control-parameter for the skyrmion motion. Moreover, the spin wave frequency dependent skyrmion motion is discussed, predicting the frequency enhanced skyrmion Hall motion. This work thus represents an essential contribution to understand the skyrmion dynamics in a FiM lattice., Comment: 25 pages, 4 figures

Magnetic skyrmions are magnetic textures with topological protection, which are expected to be information carriers in future spintronic devices. In this work, we propose a scheme to implement hybrid magnetic skyrmions (HMS) in ferrimagnets, and we study theoretically and numerically the dynamics of the HMS driven by spin-orbit torque. It is revealed that the skyrmion Hall effect depends on the skyrmion helicity and the net angular momentum ({\delta}s), allowing the effective modulation of the HMS motion through tuning Dzyaloshinskii-Moriya interaction and {\delta}s. Thus, the Hall effect can be suppressed through selecting suitable materials to better control the HMS motion. Moreover, Magnus force for finite {\delta}s suppresses the transverse motion and enhances the longitudinal propagation, resulting in the HMS dynamics in ferrimagnets faster than that in antiferromagnets., Comment: 25 pages, 6figures

Hexagonal rare-earth manganites (h-RMnO3, R = Sc, Y, Ho-Lu) exhibit intricate multiferroic properties and may be utilized for various technological applications ranging from non-volatile memories to solar cells and photo-detectors. Here, we report the epitaxial growth of hexagonal YMnO3 (h-YMO) films with different thicknesses deposited on yttria-stabilized zirconia (YSZ) substrates and their photoresponses to ultraviolet (UV) light. The structural characterizations illustrate that all the films present high quality epitaxy with out-of-plane h-YMO(0001)//YSZ(111) and in-plane h-YMO[12 3 0]//YSZ[110] relationship. Meanwhile, UV light driven photoresponses of these as-prepared films based on the planar photodetector structure with transparent Al-doped ZnO (AZO) as top electrodes are explored. It is revealed that the photocurrent will first increase and then decrease with increasing film thickness. The highest photoconductivity gain is ~387.4 observed at +4 V bias for the device with 160 nm YMO film. These results provide a guideline for hexagonal rare-earth manganites to work for UV photodetector application.

A theoretical study on the interplay of frustrated skyrmion and magnons should reveal new physics and future experiment designs. In this study, we investigate the magnon-driven dynamics of frustrated skyrmion in synthetic antiferromagnets based on micromagnetic simulations, focusing on the effect of skyrmion helicity oscillation. The oscillation speed and Hall angle of the frustrated skyrmion depending on the magnon intensity and damping constant are simulated, which demonstrates that the skyrmion helicity oscillation effectively suppresses Hall motion. The elastic scattering theory reveals that the helicity oscillation affects the scattering cross-section of injected magnons, which in turn effectively modulates the skyrmion Hall motion. This study provides a comprehensive understanding of magnon-skyrmion scattering in frustrated magnets, thus benefiting future spintronic and magnonic applications.

The controllable magnetic skyrmion motion represents a highly concerned issue in preparing advanced skyrmion-based spintronic devices. Specifically, magnon-driven skyrmion motion can be easily accessible in both metallic and insulating magnets, and thus is highly preferred over electric current control further for the ultra-low energy consumption. In this work, we investigate extensively the dynamics of skyrmion motion driven by magnon in an antiferromagnet using the collective coordinate theory, focusing on the effect of magnon polarization. It is revealed that the skyrmion Hall motion driven by circularly polarized magnon becomes inevitable generally, consistent with earlier report. Furthermore, the elastic scattering theory and numerical results unveil the strong inter-dependence between the linearly polarized magnon and skyrmion motion, suggesting the complicated dependence of the skyrmion motion on the polarization nature of driving magnon. On the reversal, the scattering from the moving skyrmion may lead to decomposition of the linearly polarized magnon into two elliptically polarized magnon bands. Consequently, a net transverse force acting on skyrmion is generated owing to the broken mirror symmetry, which in turn drives a skyrmion Hall motion. The Hall motion can be completely suppressed only in some specific condition where the mirror symmetry is preserved. The present work unveils non-trivial skyrmion-magnon scattering behavior in antiferromagnets, advancing the antiferromagnetic spintronics and benefiting to high-performance devices., 22 pages,7 figures

Reliable detection of antiferromagnetic (AFM) structures remains an open issue in experiments, although these structures such as skyrmions are suggested to play an important role in future spintronic applications. In this work, we theoretically proposed an alternative method to localize the AFM skyrmions along the direction of driving force through tuning magnetic anisotropy barriers by linear lattice defect design. The dependence of the depinning current on the magnitude and width of the defects and temperature is numerically investigated by solving the Landau-Lifshitz-Gilbert equation and also derived based on the Thiele’s theory. The stable pinning of the skyrmion for certain ranges of the injected current is clearly demonstrated, which suggests an effective way in localizing the skyrmion. Based on the calculated results, we propose a method of precise track-selecting of the AFM skyrmions, which are meaningful for future two- and three- dimensional AFM spintronic device design.

Intervertebral disc degeneration (IVDD) is associated with the apoptosis of nucleus pulposus (NP) cells. Previous studies have shown that PTEN plays crucial roles in cell survival and apoptosis. The effect of PTEN inhibitors on cell survival following IVDD has been rarely examined. In this study, we investigated the protective effect of SF1670, as a specific PTEN inhibitor, on an in vitro NP cells degenerated model.We collected human disc samples from IVDD patients and detected PTEN expression in them with different degenerated degrees. NP cells were isolated from the samples and exposed to IL-1β with or without SF1670. Then, cells viability was determined by CCK-8 assay. We also measured the levels of collagen II, p16, p53, PTEN, Akt, aggrecan, caspase 3/9, Bax, Bcl-2, and several inflammatory factors in NP cells.We found that the expression of PTEN markedly increased in severely degenerated disc tissues. The data showed that IL-1β upregulated the expressions of p16, p53, PTEN, caspase 3/9, and Bax, but decreased the expressions of collagen II, Akt, aggrecan, and Bcl-2. Surprisingly, the treatment with SF1670 could significantly reverse the regulatory effects of IL-1β. Moreover, relative levels of IL-6, IL-8, TNF-α, and MMP3/9/13 were significantly suppressed by SF1670 stimuli compared with IL-1β group.Overall, these results demonstrated that SF1670 prevented NP degradation via suppressing apoptosis and inflammation through inhibition of PTEN and activation of Akt. SF1670 may become a novel target for the therapy of IVDD in the future.

The Kitaev model on the honeycomb lattice has been receiving substantial attention due to the discovery of quantum spin liquid state associated with this model. Consequently, its classical partners such as the Kitaev-Heisenberg (KH) model and associated phase transitions become concerned. Specifically, an intermediate Kosterlitz-Thouless (KT) phase engaged in the transition from the high-temperature (T) disordered state to the low-T sixfold degenerate state is predicted in the isotropic KH model [Phys. Rev. Lett. 109, 187201 (2012)10.1103/PhysRevLett.109.187201], but so far no sufficient experimental proof has been reported. In this work, we consider an essential extension of this KH model on the honeycomb lattice by including the Kitaev exchange anisotropy that is non-negligible in realistic materials. The associated phase transitions are thus investigated using the Monte Carlo simulations. It is found that such an anisotropy will result in a degradation of the sixfold degeneracy of the ground state in the isotropic KH model down to the fourfold or twofold degenerate ground state, and the finite-T phase transitions will also be modified remarkably. Interestingly, the intermediate KT phase can be suppressed by this Kitaev exchange anisotropy. This work thus provides a more realistic description of the physics ingredient with the KH model and presents a possible explanation on absence of the intermediate phase in real materials where the Kitaev exchange anisotropy can be more or less available.

Nucleus pulposus (NP) cell proliferation plays a key role during the process of intervertebral disc degeneration (IDD). S-phase kinase-associated protein-2 (Skp2) has been proved as an important regulator for cell growth factors in vitro. Nonetheless, whether Skp2 attenuates IDD by mediating NP cell proliferation still remains unclear. Therefore, the aim of this study was to explore how Skp2 affected NP cell proliferation and the potential mechanism in vitro.In this study, we first collected different degenerated human NP samples and isolated NP cells from these tissues. NP cell degenerated model was established with IL-1β, and the cells were transfected with lentivirus to achieve Skp2 overexpression. Besides, SKPinC1 was used to suppress Skp2 expression in vitro. Western blot, RT-PCR, and immunocytofluorescence were applied to detect genetic differences among groups. Furthermore, cell viability and cell cycle were determined by CCK-8 assay and flow cytometry, respectively.Skp2 expression decreased significantly in degenerated disc samples (p0.05). IL-1β stimulation significantly promoted NP cell degeneration, which could be reversed by Skp2 overexpression (p0.05). Meanwhile, Skp2 in IDD significantly inhibited the expression level of medial p27 and promoted cell cycle by CDK2 activation (p0.05). In addition, Skp2 suppression affected NP cell proliferation in vitro.NP cells exhibited significantly inhibited proliferation ability when down-regulated the expression level of Skp2. Our findings provided a more meritorious viewpoint of Skp2 in NP cell proliferation. Furthermore, the above results suggested that Skp2 was a novel target in the treatment of IDD.

Searching for new methods controlling antiferromagnetic (AFM) domain wall is one of the most important issues for AFM spintronic device operation. In this work, we study theoretically the domain wall motion of an AFM nanowire, driven by the axial anisotropy gradient generated by external electric field, allowing the electro control of AFM domain wall motion in the merit of ultra-low energy loss. The domain wall velocity depending on the anisotropy gradient magnitude and intrinsic material properties is simulated based on the Landau-Lifshitz-Gilbert equation and also deduced using the energy dissipation theorem. It is found that the domain wall moves at a nearly constant velocity for small gradient, and accelerates for large gradient due to the enlarged domain wall width. The domain wall mobility is independent of lattice dimension and types of domain wall, while it is enhanced by the Dzyaloshinskii-Moriya interaction. In addition, the physical mechanism for much faster AFM wall dynamics than ferromagnetic wall dynamics is qualitatively explained. This work unveils a promising strategy for controlling the AFM domain walls, benefiting to future AFM spintronic applications., Comment: 17 pages, 5 figures

In this study, the accuracy of the model developed for oscillating laser-GMA hybrid welding has been improved by integrating more experimentally measured parameters, such as the droplet velocity, transient arc power, and fusion area on sheets at the transverse cross-section. The effects of lateral distance of hybrid heat source relative to the top sheet edge on heat transfer and fluid flow in weld pool are numerically simulated. It is found that with more offset of the hybrid heat source to the top sheet, a larger depression and stronger lateral flow occur in weld pool, which leads to a delayed and weak backwards flow. These characteristics of heat transfer and fluid flow play a great role in the formation of weld bead defects of lap joint configuration, such as irregularity, discontinuity, lack of fusion at the top sheet. Compared to the experimental investigation, the numerical simulation provides not only quantitative description of the occurrence of those weld bead defects but also a deep physical insight into the whole process. Thus, it is useful for the parameter optimizations and further applications of this hybrid welding process.

The oscillating laser-GMA hybrid welding tests with lap joint configuration were conducted to observe the behaviour of welding arc, metal transfer and weld pool. Temperature distribution in the resultant lap joint was monitored. Based on the observations and the resultant morphology and geometry of weld bead, effects of three important process parameters, i.e. welding speed, laser beam oscillation and lateral distance of hybrid heat source relative to top sheet edge (LDHS), on the weld bead defects were examined. Consequently, occurrence mechanisms of the weld defects were proposed. LDHS influenced the defects such as non-uniform weld bead width, discontinuity and lack of fusion at top sheet, whilst the undercutting defect occurred at the top sheet if welding speed exceeded 6 m min−1. The laser beam oscillation could disperse the high concentrated power density of single-mode laser to avoid deep penetration channel through bottom sheet, but had little effect on the weld geometry.

A three dimensional numerical model of oscillating single mode laser-GMA hybrid welding process with lap joint and arc inclination configuration has been developed for the first time. The model is used to investigate the temperature field and fluid flow corresponding to the aforesaid welding process and weld configuration. An asymmetric distribution of arc heat and a cylindrical volumetric distribution of laser heat are established to describe the heat transfer from the combined heat source to the workpieces. The droplet with predefined temperature and velocity is impinged on the weld pool at a given fillet weld angle. Arc pressure, electromagnetic force, Marangoni force and buoyancy are also considered in the model with some modifications with respect to the lap joint and arc inclination configuration. Results show that the droplet impingement process has a significant influence on the weld geometry, temperature field and fluid flow pattern due to the transfer of mass, energy and momentum into the weld pool. These unique temperature fields and flow patterns are characteristic to the lap joint and arc inclination configuration. The proposed model exhibits close correspondence with the experimental results with respect to weld geometry.

We report a systematic study on the magnetic, dielectric, and magnetoelectric (ME) properties of the Y-type hexaferrite (Ba0.4Sr1.6)Zn2(Fe11.3Al0.7)O22 single crystal. The phase diagrams were established by the observed magnetic anomalies under magnetic field and temperature scans for the in-plane and out-of-plane cases. Intrinsic large anisotropy in the magnetodielectric and converse ME effects was revealed. The spin-driven electric polarizations induced in the ab-plane and out-of-plane were found to be closely related to the transverse conical and alternating longitudinal conical spin structures, respectively. The amplitudes of varied magnetization ΔM are about ∼0.128 μB/f.u and ∼0.0178 μB/f.u. in the E oscillating between ±1 MV/m at 100 K, corresponding to the converse ME effect coefficient of ∼3500 ps/m and ∼480 ps/m for the in-plane and out-of-plane cases, respectively. All these results demonstrate the essential and unique spin-order-induced anisotropic ferroelectricity and ME properties in these Y-type hexaferrites.

High coercivity Nd25Fe40Co20Al15−xBx (x=7–15) hard magnets were prepared by a simple process of injection casting. Different from many previous investigations on nanocomposite compositions, the magnets in this work contain hard magnetic Nd2(FeCoAl)14B, Nd-rich, and Nd1+e(FeCo)4B4 phases. The magnetic properties, phase evolution, and microstructure of the as-cast and annealed magnets were investigated. As the boron content increased from 7 to 11 at%, the intrinsic coercivity Hcj of the as-cast magnet increased from 816 to 1140 kA/m. The magnets annealed at 750 °C have shown more regular and smaller grains than the as-cast alloys, especially for the x=11 alloy. The high intrinsic coercivities for the annealed alloys with x=8~11 result from the presence of small-sized grains in the microstructure. The highest Hcj of 1427 kA/m was obtained for the heat treated alloy with x=10. This work provides an alternative approach for preparing fully dense Nd-rich bulk hard magnets with relatively good properties.

In this work, we study the magnetization process of triangular heterostructures formed by a number of multilayers which are coupled antiferromagnetically by Monte Carlo simulation of an Ising model. The antiferromagnetic in-layer and ferromagnetic inter-layer couplings are considered in each stack. Interestingly, it is observed that several additional magnetization plateaus can be stabilized by the consideration of the inter-stack coupling, in addition to the main 1/3 plateau observed in bulk system. Furthermore, the widths of these plateaus are mainly determined by the lattice structure and inter-stack coupling, and the heights are only dependent on the lattice structure. Thus, our work suggests a possible method of modulating the spin orders and magnetization plateaus in synthetic triangular heterostructures through detailed tuning the lattice structure.

In this work, we study the phase diagram of a frustrated Heisenberg model with the additional next nearest neighbor four-spin interaction accounting for the spin–lattice coupling in order to understand the magnetism of iron tellurium. The experimentally identified bicollinear ground state that is always degenerate with the plaquette state in any Heisenberg-biquadratic models [Glasbrenner et al., Nat. Phys. 11, 953 (2015)] and the first-order phase transition are well reproduced, strongly confirming the essential role of the four-spin interaction related to the spin–lattice coupling [Bishop, Moreo, and Dagotto, Phys. Rev. Lett. 117, 117201 (2016)] in explaining the magnetic properties of iron tellurium. Moreover, based on the linear spin-wave theory, specific magnetic excitation in strained iron tellurium is predicted, appealing for experimental verification.

In this work, we study the rotating magnetic field driven domain wall (DW) motion in antiferromagnetic nanowires, using the micromagnetic simulations of the classical Heisenberg spin model. We show that in low frequency region, the rotating field alone could efficiently drive the DW motion even in the absence of Dzyaloshinskii-Moriya interaction (DMI). In this case, the DW rotates synchronously with the magnetic field, and a stable precession torque is available and drives the DW motion with a steady velocity. In large frequency region, the DW only oscillates around its equilibrium position and cannot propagate. The dependences of the velocity and critical frequency differentiating the two motion modes on several parameters are investigated in details, and the direction of the DW motion can be controlled by modulating the initial phase of the field. Interestingly, a unidirectional DW motion is predicted attributing to the bulk DMI, and the nonzero velocity for high frequency is well explained. Thus, this work does provide useful information for further antiferromagnetic spintronics applications., Comment: 15 pages, 5 figures;to be published in Journal of Magnetism and Magnetic Materials

In this work, we investigated the nanoscale conduction and charge transport characteristics of epitaxial VO2 thin films around the metal-insulator transition (MIT) using the Hall transport measurement and conduction atomic force microscopy. Unlike the conventional oxides, the VO2 thin films show unique transport characteristics. First, the dominant carrier type shows a critical change from electron to hole during the MIT sequence (cooling sequence) or from hole to electron during the reverse MIT sequence (heating sequence). Second, the carrier density measured during the MIT sequence is higher than that measured during the reverse MIT sequence, evidenced with a clear thermal hysteresis. Third, the volume fraction (area percentage) of the nanoscale high-conduction phase also shows a thermal hysteresis, evidenced with a larger volume fraction of the high-conduction region in the MIT sequence than the reverse MIT sequence. The first-principles calculations indicate that the dominant carrier is the hole in the monoclinic phase, while it is the electron in the rutile phase, suggesting that the unique charge transport characteristics are attributed to the structural phase transition. Our work provides a deep insight into the nanoscale conduction and charge transports in VO2 thin films.

A bioinspired structure of an artificial mushroom, made of the common polyvinyl alcohol sponge coated with charcoal, is fabricated, with high efficiency in generating cold water steam of ≈73% under 1 sun illumination, due to very high light absorption, efficient water supply, and low heat loss. In addition, the structure is very inexpensive, and thus ideal for applications in portable cold (boil‐free) steam generators for water purification and desalination.

Multiferroic BiFe1−xScxO3 ceramics with x = 0.00–0.10 were synthesized by rapid liquid phase sintering. The influences of Sc doping on the crystalline structures, dielectric, ferroelectric, and magnetic behaviors of BiFeO3 ceramics were explored. The X-ray diffraction and the Raman spectrometric analysis revealed that all the samples are nearly single phase of rhombohedral structure with the incorporation of Sc ions into BiFeO3. With increase doping concentration of x, the dielectric constant, dielectric loss, and remnant polarization for the doped BiFeO3 increase first and then drop down with further rise of x. A saturated ferroelectric polarization can be achieved at a small amount of Sc doping concentration (x

Polarization switching and energy storage properties of a series of Pb 0.97 La 0.02 Zr 0.95 Ti 0.05 O 3 (PLZT) thin films deposited on (100)-textured LaNiO 3 (LNO)-buffered Si substrates and (111)-textured Pt/Ti/SiO 2 /Si substrates were investigated. It was revealed that the PLZT films deposited on the (100)-textured LNO-buffered Si substrates prefer the (100) textured structure, while the orientation of the films deposited on the (111)-textured Pt-coated Si substrates is random. With respect to the films on the Pt-coated Si substrates, the (100) textured PLZT films have bigger compressive residual stress, larger electrical polarization, better dielectric properties, and better energy storage performances. For the (100)-orientated PLZT films, the energy density ( W s ) and efficiency ( η ) measured at room temperature are about 15.3 J/cm 3 and 56% respectively. Moreover, the better frequency stability in the range from 20 Hz to 10 kHz, and temperature stability in the range from 25 to 270 °C are demonstrated in the (100)-orientated PLZT films. These results indicate that the PLZT films with LNO bottom electrode could be potential candidate for applications in high energy storage density capacitors.

The aims of this study were to explore the correlation between the expression of EpCAM and the Wnt/β-catenin pathway in human colon cancer and its clinical significance for the evaluation of cancer prognosis. Samples from colon cancer, para-carcinoma, or benign intestinal tissue from individual patients (50) and from normal intestinal mucosal tissues (20) were obtained from the Pathology Department of the Shandong Province Binzhou People's Hospital (Shandong, China). Immunohistochemistry was used to detect the expression levels of EpCAM and β-catenin proteins in these tissues, and the prognoses of the patients from whom the samples were derived were determined on follow-up examination. The corresponding in vitro mechanistic siRNA experiments were subsequently performed in the human colon cancer cell line HCT116 to observe the regulatory effects of silencing EpCAM expression on the Wnt/β-catenin pathway. From these analyses, we determined that the expression levels of EpCAM and β-catenin were higher in cancer tissues compared with other tissues from the same patient, and that the expression of EpCAM and Wnt/β- catenin in colon cancers were positively correlated. The prognostic analysis showed an inverse correlation between EpCAM and Wnt/β- catenin expression and patient prognosis. A further examination of cellular mechanisms confirmed that the silencing of EpCAM led to decreased expression of Wnt/β-catenin, and thus reduced proliferation and increased the apoptosis ratio in the cells. These results suggest that suppression of EpCAM might be a new approach for treating colon cancer.

Based on the modified Heisenberg-Kitaev model, the effects of magnetic substitution on the magnetic properties of the honeycomb-lattice iridate [Formula: see text] [Formula: see text] are studied using Monte Carlo simulations. It is observed that the long-range zigzag state of the original system is rather fragile and can be replaced by a spin-glass state even for small substitution, well consistent with the experimental observation in Ru-substituted samples (Mehlawat et al 2015 Phys. Rev. B 92 134412). Both the disordered Heisenberg and Kitaev interactions caused by the magnetic ion-doping are suggested to be responsible for the magnetic phase transitions in the system. More interestingly, a short-range zigzag order is suggested to survive above the freezing temperature even at high magnetic impurity doping levels.

We study the thermal phase transitions of the four-fold degenerate phases (the plaquette and single stripe states) in two-dimensional frustrated Ising model on the Shastry-Sutherland lattice using Monte Carlo simulations. The critical Ashkin-Teller-like behavior is identified both in the parameter regions with the plaquette and single stripe phases, respectively. The four-state Potts-critical end points differentiating the continuous transitions from the first-order ones are estimated based on finite-size scaling analyses. Furthermore, similar behavior of the transition to the four-fold single stripe phase is also observed in the anisotropic triangular Ising model. Thus, this work clearly demonstrates that the transitions to the four-fold degenerate states of two-dimensional Ising antiferromagnets exhibit similar transition behavior., To be published in Physical Review E

The magnetically induced electric polarization behaviors in multiferroic TmMn2O5 in response to varying temperature and magnetic field are carefully investigated by means of a series of characterizations including the high precision pyroelectric current technique. Here polycrystalline rather than single crystal samples are used for avoiding the strong electrically self-polarized effect in single crystals, and various parallel experiments on excluding the thermally excited current contributions are performed. The temperature-dependent electric polarization flop as a major character is identified for different measuring paths. The magneto-current measurements indicate that the electric polarization in the low temperature magnetic phase region has different origin from that in the high temperature magnetic phase. It is suggested that the electric polarization does have multiple components which align along different orientations, including the Mn3+-Mn4+-Mn3+ exchange striction induced polarization PMM, the Tm3+-Mn4+-Tm3+ exchange striction induced polarization PTM, and the low temperature polarization PLT probably associated with the Tm3+ commensurate phase. The observed electric polarization flop can be reasonably explained by the ferrielectric model proposed earlier for DyMn2O5, where PMM and PTM are the two antiparallel components both along the b-axis and PLT may align along the a-axis. Finally, several issues on the unusual temperature dependence of ferroelectric polarizations are discussed.

In this work, we study the doping effects on the magnetic states of CuCrO2 based on the classical frustrated spin model [Lin et al., Phys. Rev. B 89, 220405(R) (2014)]. Several experimental observations can be well reproduced by the Monte Carlo simulations of the modified spin models. Our work suggests that the disorder induced by V/Al doping cooperated with the frustration in the system may contribute to the emergence of the spin glass state. Furthermore, the hole-doping by Mg2+ substituting Cr3+ enhances the quantum fluctuations and bond disorder which modulate the biquadratic exchanges, and in turn results in the promotion of the spiral phase, consistent with the experimental report., 19 pages, 7 figures, to be published in Physical Review B

The leakage behaviors of ferroelectric layered-perovskite (Bi3.15Nd0.85)Ti3O12 (BNdT) thin films deposited on Pt/TiO2/Ti/Si substrates by RF sputtering have been carefully investigated. Their I–V curves exhibit a rich diversity of conducting behaviors at different temperature and voltage ranges, which may be accounted for by various conducting mechanisms, including Ohmic behavior, Schottky emission, space-charge-limited current (SCLC), and Fowler-Nordheim tunneling effects. Their time-dependent leakage currents show a nearly linear relationship with respect to logarithmic relaxation time at initial stage ( 400 s) showing characteristics of ionic space-charge limit current relaxation.

BiFeO3 represents the most extensively investigated multiferroic due to its fascinating ferroelectric domain structures, large polarization, and multiferroic coupling, among many other emergent phenomena. Nevertheless, much less concern with the piezoelectricity has been raised while all these well addressed properties are identified in thin film BiFeO3, and bulk ceramic BiFeO3 has never been given priority of attention. In this paper, we report our experiments on the ferroelectric and piezoelectric properties as well as domain structures of BiFeO3 bulk ceramics synthesized by rapid hot-press sintering. It is revealed that these properties are strongly dependent on the microstructural quality, and the largest piezoelectric coefficient d33 = 55 pC/N with electric polarization as large as 45 μC/cm2 is obtained for the sample sintered at 800 °C, while they are only 30 pC/N and 14 μC/cm2 for the samples sintered in normal conditions at 800 °C. The two-level hierarchical stripe-like and irregular dendrite-like domain structures are observed in these hot-press sintered samples. It is suggested that the enhanced piezoelectric property is ascribed to the two-level hierarchical stripe-like domain structure which may respond more easily to electrical and strain stimuli than those irregular dendrite-like domains. The enhanced remnant polarization should be owing to the improved sample quality and large grains in the properly hot-press sintered samples.

Multiferroic BiFeO 3 thin films of huge polarization have been successfully realized by using SrRuO 3 as a buffer layer on a Pt/TiO 2 /SiO 2 /Si substrate. They consist of a single perovskite phase and are nearly randomly orientated, where the SrRuO 3 buffer layer lowers the crystallization temperature and improves the crystallinity of BiFeO 3 . With increasing deposition temperature during magnetron sputtering, they undergo an apparent grain growth and reduction in surface roughness. The multiferroic thin films deposited on the SrRuO 3 -buffered Pt/ TiO 2 /SiO 2 /Si substrate at higher temperatures show much improved polarization and reduced coercive field, together with a lowered leakage current. A huge remnant polarization (2P r ) of 150 μC/cm 2 and a coercive field (2E c ) of 780 kV/cm were measured for the BiFeO 3 film deposited at 650°C.

We describe the effects of magnetostatic interactions and film thickness on the switching properties and reversal mechanisms of periodic arrays of elongated Ni80Fe20 thin film rings. The magnetization reversal process, the switching field distributions and the transition fields between different equilibrium states are strongly affected by the inter-ring spacing. For closely packed ring arrays, sharp transitions were observed from the onion-to-vortex state due to collective magnetization reversal of the rings. In agreement with micromagnetic simulations, the range of stability of the vortex state is smaller for closely packed ring arrays compared with isolated rings of similar lateral dimensions. (Some figures in this article are in colour only in the electronic version)

In this work, we investigate the phase transitions and critical behaviors of the frustrated J1-J2-J3 Ising model on the square lattice using Monte Carlo simulations, and particular attention goes to the effect of the second next nearest neighbor interaction J3 on the phase transition from a disordered state to the single stripe antiferromagnetic state. A continuous Ashkin-Teller-like transition behavior in a certain range of J3 is identified, while the 4-state Potts-critical end point [J3/J1]C is estimated based on the analytic method reported in earlier work [Jin et al., Phys. Rev. Lett. 108, 045702 (2012)]. It is suggested that the interaction J3 can tune the transition temperature and in turn modulate the critical behaviors of the frustrated model. Furthermore, it is revealed that an antiferromagnetic J3 can stabilize the staggered dimer state via a phase transition of strong first-order character., 20 pages, 10 figures. To be published in Physical Review E

Multiferroic tunneling junction based four-state non-volatile memories are very promising for future memory industry since this kind of memories hold the advantages of not only the higher density by scaling down memory cell but also the function of magnetically written and electrically reading. In this work, we demonstrate a success of this four-state memory in a material system of NiFe/BaTiO3/La0.7Sr0.3MnO3 with improved memory characteristics such as lower switching field and larger tunneling magnetoresistance (TMR). Ferroelectric switching induced resistive change memory with OFF/ON ratio of 16 and 0.3% TMR effect have been achieved in this multiferroic tunneling structure.

Bilayered thin films consisting of Pb(Mg1/3Nb2/3)O3–PbTiO3 and (Bi3.15Nb0.85)Ti3O12 (PMN–PT/BNdT) layers have been successfully deposited on Pt/Ti/SiO2/Si substrate by RF sputtering. Their ferroelectric and dielectric behaviors can be tailored by varying the thicknesses of the two constituent ferroelectric layers. An enhancement in both remanent polarization and fatigue resistance is observed by increasing the layer thickness of BNdT, which also leads to an increase in coercive field. The bilayered ferroelectric thin films demonstrate electrical behaviors in association with space charge at low frequencies, which can account for the observed ferroelectric and fatigue properties, as confirmed by frequency and impedance studies.

Effects of excess Bi2O3 content on formation of (Bi3.15Nd0.85)Ti3O12 (BNT) films deposited by RF sputtering were investigated. The microstructures and electrical properties of BNT thin films are strongly dependent on the excess Bi2O3 content and post-sputtering annealing temperature, as examined by XRD, SEM, and P–E hysteresis loops. A small amount of excess bismuth improves the crystallinity and therefore polarization of BNT films, while too much excess bismuth leads to a reduction in polarization and an increase in coercive field. P–E loops of well-established squareness were observed for the BNT films derived from a moderate amount of Bi2O3 excess (5 mol%), where a remanent polarization 2Pr of 25.2 μC/cm2 and 2Ec of 161.5 kV/cm were shown. A similar change in dielectric constant with increasing excess Bi2O3 content was also observed, with the highest dielectric constant of 304.1 being measured for the BNT film derived from 5 mol% excess Bi2O3.

0.6Pb(Ni1/2W1/2)O3·0.4PbTiO3(0.6PNW·0.4PT) of complex perovskite structure is successfully synthesized by mechanical activation of mixed oxide composition, followed by sintering at 950°C. It exhibits a considerably stable temperature dependence of dielectric constant over the wide temperature range of −120° to 20°C, although there occurs a dielectric peak at around 74°C. Raman spectroscopic studies show the coexistence of tetragonal and pseudocubic perovskite phases on sintering at 950°C, which are attributed to the inhomogeneous distribution of PbTiO3 arising from mechanical activation. The dielectric behavior can be fine tuned by thermal annealing at 750°C, leading to phase redistribution in PNW-PT.

Order–disorder transformation triggered by mechanical activation in a perovskite structure was observed in Pb(Sc1/2Ta1/2)O3; it is simulated using a Monte Carlo algorithm, based on the competition between mechanical activation leading to disordering and the thermal diffusion recovering the ordering. The time evolution of the long-range order (LRO) from an initial ordered state shows a steady decrease at the initial stage and then becomes more or less stabilized over a prolonged period; while from the disordered initial state, LRO increases first and then stabilizes at a similar end value. Thermal diffusion is the dominant process at relatively high temperatures, leading to the disorder-to-order transformation. The effect of mechanical activation becomes significant and results in order-to-disorder transformation at relatively low temperatures. Both the mechanical activation intensity and the vacancy migration energy exert an impact on the degree of ordering and the order–disorder transformation temperature at low temperatures. Snapshot images of the simulation demonstrate the competition between thermal diffusion and mechanical activation, which refines the domain size.

Mechanical activation-induced B site order–disorder transition was observed in Pb(Mg1/3Nb2/3)O3–Pb(Mg1/2W1/2)O3 of complex perovskite structure. The disorder triggered by mechanical activation can be steadily recovered by thermal annealing at elevated temperature, as shown by XRD diffraction results. The degree of ordering calculated from Raman spectra demonstrates similar behaviors as those of XRD, except in the low ordering states, i.e. when the ordering domain size in 0.4PMN–0.6PMW is out of the coherence range of XRD. The above order–disorder transition was explained by the competition between the activation-triggered refinement of ordering domains leading to disordering and the thermal activation, which builds up the ordering domains. © 2002 Elsevier Science B.V. All rights reserved.

Based on the modified Heisenberg-Kitaev model, the effects of magnetic substitution on the magnetic properties of the honeycomb-lattice iridate [Formula: see text] [Formula: see text] are studied using Monte Carlo simulations. It is observed that the long-range zigzag state of the original system is rather fragile and can be replaced by a spin-glass state even for small substitution, well consistent with the experimental observation in Ru-substituted samples (Mehlawat et al 2015 Phys. Rev. B 92 134412). Both the disordered Heisenberg and Kitaev interactions caused by the magnetic ion-doping are suggested to be responsible for the magnetic phase transitions in the system. More interestingly, a short-range zigzag order is suggested to survive above the freezing temperature even at high magnetic impurity doping levels.

In this work, we fabricated a high performance flash-type organic nonvolatile memory transistor, which adopted polymer-electret poly(α-methylstyrene) (PαMS) and HfO2 films as hybrid charge trapping layer (CTL). Compared with a single HfO2 or PαMS CTL structure, the hybrid HfO2/PαMS CTL structure can provide enhanced charge trapping efficiency to increase the device operation speed and reduce the leakage current to boost the device reliability. The fabricated nonvolatile organic memory transistors with the hybrid CTL shows excellent electrical properties, including low operation voltage (8 V), high speed (

The pattern evolution of striped and vortex domain structures in circular ferroelectric nano-islands with in-plane polarization and charged defects is investigated using the Monte Carlo simulation based on the Landau-Devonshire phenomenological theory. The domain structures of islands undergoing different annealing processes are compared. Given embedded charge carriers at the center of islands, the domain patterns would be markedly affected as a result of the competition and balance between the electrostatic charge energy and other free energy terms in the Landau-Devonshire phenomenological theory. The symmetry of islands with different sizes and charge quantities is also analyzed. The present work provides a simple explanation of a variety of ferroelectric nano-islands and proposes an alternative promising approach to tune the domain structures and symmetry for the applications of nano-sized ferroelectric devices.