Search

Mn2−xCrxSb2 epitaxial thin films were grown on perovskite oxide single-crystal substrates using the molecular beam epitaxy technique. A magnetic phase diagram has been established for Mn2−xCrxSb2 films in the low doping region.

Stoichiometric Cr2Se3 single crystals are particular layer-structured antiferromagnets, which possess a noncollinear spin configuration, weak ferromagnetic moments, moderate magnetoresistance (MR ∼14.3%), and poor metallic conductivity below the antiferromagnetic phase transition. Here, we report an interesting >16 000% colossal magnetoresistance (CMR) effect in Ti (1.5 atomic percent) lightly doped Cr2Se3 single crystals. Such a CMR is approximately 1143 times larger than that of the stoichiometric Cr2Se3 crystals and is rarely observed in layered antiferromagnets and is attributed to the frustrated spin configuration. Moreover, the Ti doping not only dramatically changes the electronic conductivity of the Cr2Se3 crystal from a bad metal to a semiconductor with a gap of ∼15 meV but also induces a change in the magnetic anisotropy of the Cr2Se3 crystal from strong out-of-plane to weak in-plane. Further, magnetotransport measurements reveal that the low-field MR scales with the square of the reduced magnetization, which is a signature of CMR materials. The layered Ti:Cr2Se3 with the CMR effect could be used as two-dimensional (2D) heterostructure building blocks to provide colossal negative MR in spintronic devices.

Linear magnetoresistance (LMR) is usually observed in topological quantum materials and plausibly connected with the topologically nontrivial surface state with Dirac-cone-like linear dispersion because the frequently encountered large Hall resistivity can be trivially mixed into the LMR via charge inhomogeneity. Herein, by applying an optimal gate voltage to nodal-line semimetal ZrGeSe two-dimensional (2D) layers with specific thicknesses, we observe a giant nonsaturated LMR of 8 × 104% at 2 K and a magnetic field of 9 T. This giant LMR is accompanied by a very small Hall resistivity, which is inconsistent with the charge inhomogeneity mechanism. Our systematic results confirm that the giant LMR is maximized when the topological semimetal is in the "even-metal" regime and suppressed upon evolution to the normal "odd-metal" regime. The "even-to-odd" transition is universal regardless of the thicknesses of the crystals. A comparison with Abrikosov's quantum LMR theory indicates that the observed LMR cannot be trivial.

Linear magnetoresistance (LMR) is a special case of a magnetic-field induced resistivity response, which has been reported in highly disordered semiconductor systems and in topological materials. In this work, we observe LMR effect in half-metallic perovskite Sr2CrMoO6 thin films, of which the maximum MR value exceeds +1600% at 2 K and 14 T. It is an unusual behavior in ferrimagnetic double perovskite material like Sr2CrMoO6, which are known for intrinsic tunneling-type negative magnetoresistance. In the thin films, the high carriers’ density (~1022 cm−3) and ultrahigh mobility (~104 cm2 V−1 s−1) provide a low-resistivity (~10 nΩ·cm) platform for spin-polarized current. Our DFT calculations and magnetic measurements further support the half-metal band structure. The LMR effect in Sr2CrMoO6 could possibly originate from transport behavior that is governed by the guiding center motion of cyclotron orbitals, where the magnetic domain structure possibly provides disordered potential. The ultrahigh mobility and LMR in this system could broaden the applications of perovskites, and introduce more research on metallic oxide ferri-/ferro-magnetic materials.

We report the synthesis of transition-metal-doped ferromagnetic elemental single-crystal semiconductors with quantum oscillations using the physical vapor transport method. The 7.7 atom% Cr-doped Te crystals (Cr_Te) show ferromagnetism, butterfly-like negative magnetoresistance in the low temperature (< 3.8 K) and low field (< 0.15 T) region, and high Hall mobility, e.g., 1320 cm2 V-1 s-1 at 30 K and 350 cm2 V-1 s-1 at 300 K, implying that Cr_Te crystals are ferromagnetic elemental semiconductors. When B // c // I, the maximum negative MR is -27% at T = 20 K and B = 8 T. In the low temperature semiconducting region, Cr_Te crystals show strong discrete scale invariance dominated logarithmic quantum oscillations when the direction of the magnetic field B is parallel to the [100] crystallographic direction and show Landau quantization dominated Shubnikov-de Haas (SdH) oscillations for B // [210] direction, which suggests the broken rotation symmetry of the Fermi pockets in the Cr_Te crystals. The findings of coexistence of multiple quantum oscillations and ferromagnetism in such an elemental quantum material may inspire more study of narrow bandgap semiconductors with ferromagnetism and quantum phenomena., 25 pages, 25 figures

Ferroelectrics are appealing candidates for photovoltaic applications. In this study, Bi5FeTi3O15 (BFTO) single layer and ZnO/BFTO bilayer films were deposited onto 0.7 wt% Nb-doped SrTiO3 (NSTO) electrically conducting single-crystal substrates to form Ag/BFTO/NSTO and Ag/ZnO/BFTO/NSTO photovoltaic devices. It was found that the insertion of an n-type semiconducting ZnO layer eliminates the built-in electric field between the Ag electrode and the BFTO film and results in the formation of a BFTO/ZnO p–n junction with a built-in electric field whose direction points to the BFTO film. These effects, together with the depolarization field within the BFTO film, provide a favorable energy level alignment for efficient electron extraction. As a result, the short circuit photocurrent density (Jsc) was improved by nearly 50 fold to 2.2 mA cm−2 and the output power density was increased by 15 fold to 0.09 mW cm−2 under ultraviolet light (λ = 405 nm) illumination. Upon the reversal of the ferroelectric polarization direction from downward to upward, the Jsc and the open circuit voltage (Voc) were increased by 2.5 and 4 fold for the Ag/BFTO/NSTO device and by 2.83 and 8.5 fold for the Ag/ZnO/BFTO/NSTO device, respectively. This work provides an effective way for developing efficient ferroelectric and semiconductor based photovoltaic devices.

In quantum materials, the Fermi surface and physical behaviors are particularly sensitive to the crystal quality and composition, while it is difficult to obtain a large quantity of quasi-continuou...

We report the structural, dielectric, ferroelectric and magnetic properties of (1-x)BiFe0.95Ga0.03Mn0.02O3−xBaTiO3 (BFGMO−xBTO) lead-free ceramics. Structural characterizations demonstrate that the BFGMO forms single-phase solid solutions with the BTO within the doping level of x = 0.3–0.65. With increasing the content of BTO the dielectric constant and ferroelectric Curie temperature shift towards lower temperatures, exhibiting relaxor-like ferroelectric behaviors. Moreover, the remnant polarization reaches the maximum value of 2Pr ~27.67 μC/cm2 at x = 0.35 near the morphotropic phase boundary. At room temperature, remnant magnetization increases - to the maximal value of 2Mr ~0.584 emu/g at x = 0.45, which is attributed to local lattice distortion and destruction of the spiral antiferromagnetic spin structure upon the doping of BTO. The coexistence of ferroelectric and ferromagnetic performance at room temperature makes the environment-friendly BFGMO−xBTO ceramics potential candidate for multiferroic device applications.

Bi thin films were grown on (111)-oriented 0.7Pb(Mg1/3Nb2/3)O3–0.3PbTiO3 (PMN–PT) single-crystal substrates by pulsed laser deposition. Resistance of Bi/PMN–PT could be modulated by asymmetrical bipolar electric field in a reversible and nonvolatile manner at 300 K. By tuning asymmetrical bipolar electric field, different nonvolatile strain states could be generated in PMN–PT and transferred to Bi thin film, which leads to different nonvolatile resistance states. Furthermore, different resistance states of the Bi films could be achieved under different magnetic field at 300 K. The ferroelastic strain- and magnetic-field-modulated resistive properties in Bi/PMN–PT suggest a promising approach for multistate resistive memories.

The direct measurement of flexoelectric coefficients in epitaxial thin films is an unresolved problem, due to the clamping effect of substrates which induces a net strain (and hence parasitic piezoelectricity) in addition to strain gradients and flexoelectricity. Herein, we propose and demonstrate the use of van der Waals epitaxy as a successful strategy for measuring the intrinsic (clamping-free = flexoelectric coefficients of epitaxial thin films. We have made, measured, and compared BaTiO3 and SrTiO3 thin film capacitor heterostructures grown both by conventional oxide-on-oxide epitaxy and by van der Waals oxide-on-mica epitaxy, and found that, whereas the former is dominated by parasitic piezoelectricity, the response of the latter is truly flexoelectric. The results are backed by theoretical calculations of the film-substrate mechanical interaction, as well as by direct measurements that confirm the strain-free state of the films. van der Waals epitaxy thus emerges as powerful new tool in the study of flexoelectricity and, in particular, they finally allow exploring flexoelectric phenomena at the nanoscale (where strain gradients are highest) with direct experimental knowledge of the actual flexoelectric coefficients of thin films., This work was supported by the National Natural Science Foundation of China (Grants No. 12174174, No. 51962020, No. 51972157, No. 51702149, No. 11604135, and No. 11964017) and the Natural Science Foundation of Jiangxi Province (Grants No. 20212ACB214011, No. 20202ZDB01006, and No. 20192ACB21017) were also acknowledged. G.C. also acknowledges financial support from Project No. PID2019-108573GB-C21 funded by MCIN/AEI/10.13039/501100011033 and Severo Ochoa Grant No. SEV-2017-0706. L.S. thanks for support from Nanchang University.

SrIrO3 (SIO) thin films were epitaxially grown on (001)-oriented 0.7Pb(Mg1/3Nb2/3)O3-0.3PbTiO3 (PMN-PT) single-crystal substrates. Upon applying electric fields to the piezoelectric PMN-PT along the thickness direction, the electronic transport properties of SIO films can be in situ tuned and modulated by non-180° ferroelectric domain rotation-induced strain, piezoelectric strain, and rhombohedral-to-tetragonal structural phase transition-induced strain in the PMN-PT layer, respectively. Moreover, the weak negative magnetoresistance (MR) of the 60-nm SIO films could be modified by applying an electric field to the PMN-PT layer. At T = 2 K, upon the application of E = 4 kV/cm to the PMN-PT, MR at H = 9 T is reduced by 14.2% as compared to that under zero electric field, indicating in-plane compressive strain-induced suppression of the influence of quantum corrections to the conductivity in the SIO film. These results demonstrate that the electric-field controllable lattice strain is a simple approach to get insight into the strain-property relationships of 5 d iridate thin films.

Correction for ‘Magnetotransport and magnetic properties of Cr-modified Mn2Sb epitaxial thin films’ by Ting-Wei Chen et al., Phys. Chem. Chem. Phys., 2023, 25, 5785–5794, https://doi.org/10.1039/D2CP05442F.

Stoichiometric Cr

Quaternary alloy ${\mathrm{Ga}}_{1\ensuremath{-}x}{\mathrm{Mn}}_{x}{\mathrm{As}}_{1\ensuremath{-}y}{\mathrm{P}}_{y}$ hosts magnetic and electronic properties that can be tuned by varying the P concentration ``$y$'', Mn concentration ``$x$'' and by annealing. In this work we make use of this tunability to probe the origin of the anomalous Hall effect (AHE) in ${\mathrm{Ga}}_{1\ensuremath{-}x}{\mathrm{Mn}}_{x}{\mathrm{As}}_{1\ensuremath{-}y}{\mathrm{P}}_{y}$ thin films grown on GaAs that host perpendicular magnetic anisotropy. Specifically, we find that AHE in this class of materials is determined primarily by two contributions: an intrinsic band component arising from the Berry curvature, and a component determined by hopping conduction. As we vary the properties of ${\mathrm{Ga}}_{1\ensuremath{-}x}{\mathrm{Mn}}_{x}{\mathrm{As}}_{1\ensuremath{-}y}{\mathrm{P}}_{y}$ from the metallic to the semi-insulating regime by changing the value of $y$ and by postgrowth annealing, we observe a clear crossover from a Berry-curvature-induced AHE to one that is caused by hopping. The transition occurs approximately at the point where the numbers of localized and itinerant holes become comparable. In this hopping regime, the conductivity follows the Efros-Shklovskii scaling law versus temperature indicating the presence of a Coulomb gap, but the AHE remains robustly present. These results indicate that ${\mathrm{Ga}}_{1\ensuremath{-}x}{\mathrm{Mn}}_{x}{\mathrm{As}}_{1\ensuremath{-}y}{\mathrm{P}}_{y}$ can host an interesting interplay between magnetism and Coulomb interactions.

A series of Cr-doped In2-xCrxO3 (ICO) semiconductor thin films were epitaxially grown on (111)-oriented 0.71Pb(Mg1/3Nb2/3)O3-0.29PbTiO3 (PMN-0.29PT) single-crystal substrates by the pulsed laser deposition. Upon the application of an electric field to the PMN-0.29PT substrate along the thickness direction, we realized in situ, reversible, and nonvolatile control of the electronic properties and Fermi level of the films, which are manifested by abundant physical phenomena such as the n-type to p-type transformation, metal-semiconductor transition, metal-insulator transition, crossover of the magnetoresistance (MR) from negative to positive, and a large nonvolatile on-and-off ratio of 5.5 × 104% at room temperature. We also strictly disclose that both the sign and the magnitude of MR are determined by the electron carrier density of ICO films, which could modify the s-d exchange interaction and weak localization effect. Our results demonstrate that the ferroelectric gating approach using PMN-PT can be utilized to gain deeper insight into the carrier-density-related electronic properties of In2O3-based semiconductors and provide a simple and energy efficient way to construct multifunctional devices which can utilize the unique properties of composite materials.

Enhanced green and red upconversion emissions under 980 nm excitation are observed in Ba0.85−xCa0.15TiO3:0.75%Er3+/xIn3+ lead-free ferroelectric ceramics which were synthesized by solid state reaction method. With increasing In3+ ions doping level from x = 0% mol the green and red emission intensities increase and reach the maximum at x = 1.75% mol. The maximum intensity of green emission at 550 nm is 20 times larger than In3+ ions undoped samples, which is unprecedented for Er3+-doped perovskite ferroelectric materials. Based on the ultraviolet-visible-near infrared absorption spectra, the enhancement of the luminescence intensity of the A-site In3+ doped Ba0.85−xCa0.15TiO3:0.75%Er/xIn ceramics is attributed to In3+-doping-induced relative increase in isolate Er3+ and decrease in the clustered-Er3+. The effects of In3+ doping on the crystal structure, dielectric, ferroelectric, piezoelectric properties of the ceramics were also studied and discussed.

Single-phase (00 l)-oriented Bi2Te3 topological insulator thin films have been deposited on (111)-oriented ferroelectric 0.71Pb(Mg1/3Nb2/3)O3-0.29PbTiO3 (PMN-PT) single-crystal substrates. Taking advantage of the nonvolatile polarization charges induced by the polarization direction switching of PMN-PT substrates at room temperature, the carrier density, Fermi level, magnetoconductance, conductance channel, phase coherence length, and quantum corrections to the conductance can be in situ modulated in a reversible and nonvolatile manner. Specifically, upon the polarization switching from the positively poled Pr+ state (i.e., polarization direction points to the film) to the negatively poled Pr- (i.e., polarization direction points to the bottom electrode) state, both the electron carrier density and the Fermi wave vector decrease significantly, reflecting a shift of the Fermi level toward the Dirac point. The polarization switching from Pr+ to Pr- also results in significant increase of the conductance channel α from -0.15 to -0.3 and a decrease of the phase coherence length from 200 to 80 nm at T = 2 K as well as a reduction of the electron-electron interaction. All these results demonstrate that electric-voltage control of physical properties using PMN-PT as both substrates and gating materials provides a simple and a straightforward approach to realize reversible and nonvolatile tuning of electronic properties of topological thin films and may be further extended to study carrier density-related quantum transport properties of other quantum matter.

We prepared 300-nm GeTe thin films on (111)-oriented and piezoelectrically active 0.71 Pb(Mg1/3Nb2/3)O3-0.29PbTiO3 (PMN-0.29 PT) single-crystal substrates by the pulsed laser deposition and investigated the effects of in situ electric-field-controllable non-180° ferroelastic domain switching of the PMN-0.29 PT on the electronic properties of the GeTe films. The in-plane strain of the PMN-0.29 PT could be modulated continuously and reversibly by electric fields in a nonvolatile manner and could be effectively transferred to the GeTe films. Based on this, we realized reversible and nonvolatile resistance switching and obtained multilevel stable nonvolatile resistance states with good stability and endurance at T = 300 K by applying appropriate asymmetrical bipolar electric fields to the PMN-0.29 PT(111) substrates along the thickness direction. Such heterostructures may be used for multilevel data storage that allows each unit to store multiple bits of information and thus improve the memory density. Our investigation would be beneficial for the fabrication of nonvolatile memory devices using PMN-xPT-based heterostructures. Keywords: Ferroelastic strain, Electronic transport, PMN-PT, Heterostructure, Strain effect

Motivated by the fact that holes in the ${\mathrm{Ga}}_{1--x}{\mathrm{Mn}}_{x}\mathrm{As}$ family of ferromagnetic semiconductors play a key role in determining their ferromagnetic properties, we have measured hole concentrations in a series of three ${\mathrm{Ga}}_{1--x}{\mathrm{Mn}}_{x}{\mathrm{As}}_{1--y}{\mathrm{P}}_{y}$ alloys grown by molecular beam epitaxy with varying amounts of phosphorus. This was carried out by Hall effect measurements, after eliminating the effect of the anomalous Hall term, and thus isolating the ordinary Hall term that directly provides the concentration of freely moving holes. Comparing these Hall effect results with total hole concentrations obtained from the number of acceptors and compensating donors as given by structural and magnetization measurements, we find that the number of itinerant holes (i.e., holes that contribute to the Hall effect) is significantly less than the total hole concentration. This indicates that a considerable fraction of the holes arising from Mn acceptors are localized. We find, furthermore, that the degree of such localization increases with the concentration of phosphorus in the ${\mathrm{Ga}}_{1--x}{\mathrm{Mn}}_{x}{\mathrm{As}}_{1--y}{\mathrm{P}}_{y}$ alloy. Our results indicate that the Curie temperature (and, by extension, other magnetic properties) described by the Zener model in ferromagnetic semiconductors of the ${\mathrm{Ga}}_{1--x}{\mathrm{Mn}}_{x}\mathrm{As}$ family are determined by the itinerant holes rather than by the total hole concentration. Finally, our results also indicate that ferromagnetism in these alloys vanishes when the total hole concentration falls below a certain Mott-like threshold, suggesting that the holes (both localized and itinerant) reside in the acceptor impurity band created by the presence of Mn acceptors.

Flexoelectricity is apparently linearized with the dielectric permittivity and therefore regarded as an inherent dielectric response of solid dielectrics. Herein, we study the role of defect dipole to flexoelectricity by selecting several typical linear dielectrics, wherein the external factors including the surface piezoelectricity, ferroelectricity, and semiconducting interface are strictly eliminated. It is found that the defect dipoles could result in several times enhancement for both the flexoelectric coefficient and the flexocoupling coefficient of the linear dielectrics. The output of this work indicates that introducing defects was a general approach to improve the flexoelectric response.

We report on the growth of high-quality stoichiometric layered Cr

We report the epitaxial growth of the $\mathrm{Cr}$-doped ${\mathrm{In}}_{2\ensuremath{-}x}{\mathrm{Cr}}_{x}{\mathrm{O}}_{3}$ (x = 0.05) ($\mathrm{Cr}$:${\mathrm{In}}_{2}{\mathrm{O}}_{3}$) semiconducting thin films on perovskite-type (111)-oriented $0.7\mathrm{Pb}({\mathrm{Mg}}_{1/3}{\mathrm{Nb}}_{2/3}){\mathrm{O}}_{3}$\ensuremath{-}$0.3{\mathrm{Pb}\mathrm{Ti}\mathrm{O}}_{3}$ (PMN-PT) ferroelectric single-crystal substrates in the form of ferroelectric field-effect devices that allow us to obtain an in situ tuning of the electron carrier density and magnetoresistance (MR) as well as the resistance in a reversible and nonvolatile manner, thereby stringently disclosing the relationship between the MR and the electron carrier density. Specifically, for the thinnest 25-nm $\mathrm{Cr}$:${\mathrm{In}}_{2}{\mathrm{O}}_{3}$ film the polarization switching of the PMN-PT from the positively polarized ${P}_{r}^{+}$ state to the negatively polarized ${P}_{r}^{\ensuremath{-}}$ state results in a large increase in the resistance and MR. Particularly, at T = 10 K, the polarization switching induces reversible and nonvolatile changes in the magnitude and sign of MR, demonstrating strong coupling between the MR and the electron carrier density. Moreover, regardless of the polarization states of PMN-PT, MR for films with different thicknesses can be quite well described by a combination of the two-band model and the semiempirical model proposed by Khosla and Fischer based on which the positive MR (PMR) and negative MR (NMR) could be disentangled into positive component [MR(+)] and negative component [MR(\ensuremath{-})], respectively. We find that the polarization-switching-induced large decrease in the PMR and the change in the sign of MR from positive to negative is mainly due to the rapid decrease in the MR(+), demonstrating that the coupling between MR(+) and electron carrier density plays a dominant role in controlling the magnitude and sign of MR.

Harvesting environmental energy to generate electricity is a key scientific and technological endeavour of our time. Photovoltaic conversion and electromechanical transduction are two common energy-harvesting mechanisms based on, respectively, semiconducting junctions and piezoelectric insulators. However, the different material families on which these transduction phenomena are based complicate their integration into single devices. Here we demonstrate that halide perovskites, a family of highly efficient photovoltaic materials1,2,3, display a photoflexoelectric effect whereby, under a combination of illumination and oscillation driven by a piezoelectric actuator, they generate orders of magnitude higher flexoelectricity than in the dark. We also show that photoflexoelectricity is not exclusive to halides but a general property of semiconductors that potentially enables simultaneous electromechanical and photovoltaic transduction and harvesting in unison from multiple energy inputs., This work was supported by the National Natural Science Foundation of China under grant nos. 51962020, 51972157, 11574126 and 11604135, and partly by the National Key Research and Development Plan of China (2017YFB0406300). L.S. and S.K. thank Nanchang University for support. G.C. acknowledges support from the Generalitat de Catalunya (Grant 2017 SGR 579) and from MINECO (National Plan MAT2016-77100-C2-1-P and Severo Ochoa SEV-2017-0706). M.S. acknowledges the support of MINECO through grants no. MAT2016-77100-C2-2-P and no. SEV-2015-0496, Generalitat de Catalunya (grant no. 2017 SGR1506) and the European Research Council under the European Union’s Horizon 2020 research and innovation programme (grant no. 724529). We thank D Torres for the graphic design of Fig. 2a,b.

A series of erbium- and indium-doped 0.965K0.40Na0.58Li0.02Nb0.96Sb0.04O3–0.035Bi0.5K0.5ZrO3:0.25%Er/xIn lead-free piezoelectric ceramics with upconversion photoluminescence (UCPL) properties were prepared by the conventional solid state reaction. A systematical investigation into the effects of In3+ doping on the structural, dielectric, ferroelectric, piezoelectric, and UCPL properties of the ceramics was carried out. The distribution of Er3+-sites could be modified by In3+ doping according to the analysis of UV–Vis-NIR absorption cross-section, resulting in improved piezoelectric and photoluminescence properties of the ceramics. The optimized comprehensive properties are performed by the x = 0.25% samples of which the piezoelectric coefficient d33 ~ 257 pC/N, Curie temperature TC ~ 273 °C, remanent polarization Pr ~ 12.5 µC/cm2, dielectric constant er ~ 1551, and d33 ~ 257 pC/N which is the supreme piezoelectric coefficient achieved in KNN-based UCPL ceramics as of now. The results demonstrate that erbium and indium co-doped KNN-based ceramics may have potential applications in electro-optical devices.

Exchange bias in the bilayer of half-metallic La0.7Sr0.3MnO3 and multiferroic BiFeO3 has been applied for the electric field control of magnetization, which is strongly limited by the much low blocking temperature of about 100 K (Phys. Rev. Lett. 105, 027201 (2010)). One possible solution is to strengthen the interfacial exchange coupling, thus another half-metallic oxide Sr2FeMoO6 is selected. Tetragonal-like BiFeO3 has been successfully fabricated on (0 0 1) SrTiO3 substrate using Sr2FeMoO6 as buffer layer. By replacing the exchange coupling between Fe and Mn ions in BiFeO3/La0.7Sr0.3MnO3 bilayer, stronger exchange couplings between Fe and Fe ions are established at the interface, and the blocking temperature has been significantly increased to 160 K. A second blocking temperature at 110 K due to the exchange coupling between Fe and Mo ions is also observed. Detailed magnetization measurements confirm the conventional mechanism of exchange coupling between ferromagnetic and antiferromagnetic layers and exclude the contribution from surface spin glass. Furthermore, BiFeO3 still retains excellent ferroelectric properties with Sr2FeMoO6 acting as ferromagnetic conducting electrode, which may have important applications in multiferroic spintronics devices.

Reversible and nonvolatile electric-field control of the physical properties of topological insulators is essential for fundamental research and development of practical electronic devices. Here, we report the integration of topological insulator films with ferroelectric Pb(Mg1/3Nb2/3)O3-PbTiO3 (PMN-PT) single crystals in the form of ferroelectric field-effect devices that allow us to tune the electronic properties of topological insulator films in a reversible and nonvolatile manner. Specifically, gating of Cr-doped Bi2Se3 films with the PMN-PT layer is shown to provide a means to reversibly tune and modulate the carrier density and carrier type, as well as its other properties, such as the conductance, magnetoconductance, Fermi level, phase coherence length, and screening factor of electron–electron interaction by polarization switching at room temperature. These findings provide a simple and direct approach for probing the quantum transport properties of topological insulator films through ferroelectric gating by using PMN-PT. The combination of topological insulators with both ferroelectrically and piezoelectrically active PMN-PT thus offers a promising step toward exploring topological insulator/ferroelectric(piezoelectric) hybrid devices that could utilize not only the ferroelectric field-effect of topological insulator/PMN-PT structures but also the unique properties of respective materials. Electric gating can tune the properties of topological insulators, modifying the carriers’ density and type and Fermi level. Several gating materials can be used, but finding materials that allow the manipulation of these properties in a reversible and nonvolatile way at room temperature while being compatible with solid-state electronics is difficult. Now, an international team of researchers led by Ren-Kui Zheng, Yu Wang and Yu-Kuai Liu demonstrated the ferroelectric gating of the topological insulator Bi2Se3 doped with Cr, using single crystals of the perovskite material Pb(Mg1/3Nb2/3)O3-PbTiO3. They fabricated field-effect transistors in which they achieved electric-field control of the carrier density and type and of the Fermi level of the topological insulator through polarization switching of the ferroelectric layer. These results represent a step forward in the development of practical electronic devices based on topological insulators.

Superconducting thin films of FeSe0.5Te0.5 are epitaxially grown on piezoelectric 0.71Pb(Mg1/3Nb1/2)O3-0.29PbTiO3 (PMN-PT) single-crystal substrates. Upon the application of an electric field to the PMN-PT along the thickness direction the superconducting properties of the FeSe0.5Te0.5 films, such as the normal-state resistance, superconducting phase transition temperature, upper critical field, critical current, and coherence length are in situ modified via the ferroelectric polarization rotation, converse piezoelectric effect, and structural phase transition of the PMN-PT. Our findings demonstrate that the combination of superconducting thin films with piezoelectrically active PMN-PT offers a promising approach for exploring the intrinsic lattice strain effects of iron-based superconducting systems.

A series of In3+-doped Ba0.85Ca0.15TiO3:0.75%Er3+/xIn3+ (BCT:Er/xIn) lead-free piezoelectric ceramics with excellent upconversion luminescence were synthesized by the solid state reaction method. The effects of In3+ content on the crystal structure, ferroelectric, dielectric, piezoelectric, and upconversion luminescence properties were systematically studied. Under 980 nm excitation, a giant enhancement of the green emission (550 nm) by 10 times is achieved upon 2.5% mol In3+ doping, which is rarely observed in rare-earth ions-doped perovskite ferroelectric materials. The ultraviolet-visible-near infrared absorption measurements show that the In3+ doping may improve the dissolution of Er3+ ions and modify the isolate-/clustered-Er3+ ratio for x ≤ 2.5%, resulting in the enhancement of the absorption cross-section, thereby contributing to the enhancement of green luminescence. Unfortunately, the In3+ doping suppresses the ferroelectric and piezoelectric properties of the BCT:Er/xIn ceramics. This problem can be resolved by adding a small amount (1 mol%) of Yb3+ to the BCT:Er/xIn ceramics to restore their good ferroelectric and piezoelectric properties. Such In3+ and rare-earth ions co-doped ceramics with greatly enhanced upconversion luminescence and good ferroelectricity and piezoelectricity may have potential applications in electro-optical devices.

The electric-field control of resistance change (ΔR/R) and magnetic properties has been investigated in the LaMnO3(LMO)/0.71Pb(Mg1/3Nb2/3)O3-0.29PbTiO3 (PMN-PT)(0 1 1) heterostructure. When the unipolar electric field (E) increases beyond the coercive field of PMN-PT, the ΔR/R vs E curve transforms from a loop-like behavior to a butterfly-like one. The electric-field-induced non-linear strain effect in the PMN-PT substrate realizes the modulation between low and high resistance states at room temperature. Moreover, different freezing temperatures of the LMO film are observed as the PMN-PT substrate is in the fully negative ( P r - ) and partially positive ( P r / / ) polarization states. The observation of less magnetization for P r / / state than that for P r - state indicates that the in-plane tensile strain is beneficial to the Jahn-Teller distortion.

In this paper, p -type Cu 2 O thin films have been epitaxially grown on n -type semiconducting (001) oriented Nb-SrTiO 3 (NSTO) substrates with different Nb doping concentration by pulsed laser deposition technique. X-ray diffraction and high resolution transmission electron microscopy reveal a cube-on-cube epitaxial relationship between Cu 2 O and NSTO. It is found that the deposition temperature, the thickness of Cu 2 O films and the Nb doping concentration of NSTO substrates have critical impact on the photovoltaic (PV) properties of the Cu 2 O/NSTO heterojunction devices. A maximum PV performance is observed in ITO/Cu 2 O/NSTO device when the deposition temperature, film thickness and Nb doping concentration of NSTO are 550 °C, 76 nm, and 0.7 wt% NSTO, respectively. The optimized PV output corresponds to the open circuit voltage, short-circuit current density, fill factor and photovoltaic conversion efficiency about 0.45 V, 1.1 mA/cm 2 , 46% and 0.23%，respectively. This work offers an insight into the strategy for developing and designing novel optoelectronics of NSTO-based oxide heterostructures.