Hua Tian

Electric field manipulation of magnetization at room temperature in multiferroic CoFe2O4/Pb(Mg1/3Nb2/3)0.7Ti0.3O3 heterostructures

Multiferroic heterostructures were fabricated by growing ferrimagnetic CoFe2O4 films on ferroelectric Pb(Mg1/3Nb2/3)0.7Ti0.3O3 substrates using pulsed laser deposition. Upon applying an electric field, the in-plane magnetization of the heterostructures increases and the out-of-plane magnetization decreases. Sharp and reversible changes in magnetization under electric field were also observed for the poled sample. The relative change in magnetization-electric field hysteresis loops were obtained for both the in-plane and out-of-plane magnetizations. Analysis of the results suggests that the electric field induced change in magnetic anisotropy via strain plays an important role in the magnetoelectric coupling in the heterostructures.

Resistive switching effect in SrTiO3−δ∕Nb-doped SrTiO3 heterojunction

The authors report on the fabrication and properties of SrTiO3−δ∕Nb-doped SrTiO3 heterojunctions. The current-voltage curves of these junctions show hysteresis and remarkable resistive switching behavior. Hysteresis was also observed in the capacitance-voltage curves of these junctions. Upon applying voltage pulses, the resistance of the heterojunctions can be switched between different states and the relaxation of the junction current after switching follows the Curie–Von Schweidler law. The results were discussed by considering the role of defects in the interfacial depletion region of the heterojunctions. This work indicates that heterojunctions composed of two oxides can also show the switching effect, which is useful for applications.

Strain induced magnetoelectric coupling between magnetite and BaTiO3

Magnetite (Fe3O4) thin films have been grown on ferroelectric BaTiO3 (BTO) single crystal substrates by pulsed laser deposition. Transmission-electron microscope observations demonstrate the orientation relationship between Fe3O4 and BTO as [400]Fe3O4∥[200]BTO and [004]Fe3O4∥[002]BTO. Experimental measurements of magnetization, coercivity and remanent magnetization of the films show abrupt jumps at around phase transition temperatures of BTO and opposite jump signs are observed for the in-plane and out-of-plane measurements. The magnetization jumps can be suppressed by a strong external magnetic field. These results were discussed in terms of the interface strain induced changes of magnetic domain structure in the Fe3O4 film. This work demonstrates the presence of strong magnetoelectric coupling between Fe3O4 and BTO.

Effect of oxygen content and superconductivity on the nonvolatile resistive switching in YBa2Cu3O6+x/Nb-doped SrTiO3 heterojunctions

The authors report on the resistive switching effect in YBa2Cu3O6+x/Nb-doped SrTiO3 heterojunctions. The current-voltage curves of these heterojunctions show hysteresis, which increases with decreasing temperature and oxygen content. Multiresistance states are realized by voltage pulses with different amplitudes. The relaxation of the junction current after switching follows the Curie–Von Schweidler law. More interestingly, the resistance of the low resistance state for the heterojunction shows a metallic behavior with a remarkable drop at Tc. The results were discussed in terms of the trapping-detrapping process via oxygen vacancies near the interface of the heterojunction and the conducting filaments through the junction barrier.

Rectifying property and giant positive magnetoresistance of Fe3O4/SiO2/Si heterojunction

Fe3O4∕SiO2∕Si heterojunction was fabricated by growing Fe3O4 film on an n-typed Si wafer with the native SiO2 buffer layer using the pulsed laser deposition. Transmission electron microcopic study shows the high quality of the heterojunction interfaces and the SiO2 layer is 2.5nm thick. This junction shows a backward diodelike rectifying behavior and an anomalously giant positive magnetoresistance (MR) for the large reverse bias voltages. The temperature dependence of MR shows a peak around the Verwey transition temperature with a maximum MR of 87% under a −2V bias voltage. The results were discussed by considering the band structure of the heterojunction and the effect of the reverse bias voltage.

Copper-catalyzed N-arylation and aerobic oxidation: one-pot synthesis of tetrahydroisoquinolino[2,1-a]quinazolinone derivatives

An efficient and practical copper-catalyzed one-pot method for synthesis of tetrahydroisoquinolino[2,1-a]quinazolinone derivatives has been developed, and the corresponding target products were prepared in moderate to good yields. The one-pot approach underwent sequential copper-catalyzed N-arylation, intramolecular aerobic oxidative cyclization, and the newly synthesized products provided diverse structures for screening of biological molecules.

Oxygen electromigration induced nonvolatile resistance switching at Ag/La2CuO4+x interface

The authors report on the temperature dependence of electronic transport property of Ag/La2CuO4+x (LCO) heterostructures with different oxygen contents. Bipolar resistance switching was observed in the sample with larger oxygen content and disappears below 200 K, consistent with the characteristic temperature of oxygen migration in LCO. The resistance relaxation of the low resistance state shows similar behavior as that of oxygen diffusion in LCO and vanishes below 200 K. Analysis of the results strongly indicates that the resistance switching results from the modulation of Schottky barrier by oxygen electromigration at the interface.

Chiral Cyclic Ligand-Enabled Iridium-Catalyzed Asymmetric Arylation of Unactivated Racemic Allylic Alcohols with Anilines

A highly enantioselective arylation of unactivated racemic secondary allylic alcohols with aniline derivatives has been developed. The transformation was enabled by an iridium-chiral cyclic phosphoramidite complex in the presence of boron trifluoride diethyl etherate as the promoter, and the reactivity and enantioselectivity of the substrates were tuned by the variation of our newly developed chiral cyclic phosphoramidite ligands together with temperature and solvents. The method shows advantages including use of the readily available starting materials, an operationally convenient protocol, full regioselectivity and excellent enantioselectivity, and tolerance of many functional groups with water as the only byproduct.

Transition metal-free intramolecular regioselective couplings of aliphatic and aromatic C-H bonds.

Cross-dehydrogenative couplings of two different C-H bonds have emerged as an attractive goal in organic synthesis. However, achieving regioselective C-H activation is a great challenge because C-H bonds are ubiquitous in organic compounds. Actually, the regioselective couplings promoted by enzymes are a common occurrence in nature. Herein, we have developed simple, efficient and general transition metal-free intramolecular couplings of alphatic and aromatic C-H bonds. The protocol uses readily available aryl triazene as the radical initiator, cheap K2S2O8 as the oxidant, and the couplings were performed well with excellent tolerance of functional groups. Interestingly, α-carbon configuration of some amino acid residues in the substrates was kept after the reactions, and the couplings for substrates with substituted phenylalanine residues exhibited complete β-carbon diastereoselectivity for induction of the chiral α-carbon. Therefore, the present study should provide a novel strategy for regioselective cross-dehydrogenative couplings of two different C-H bonds.

CCDC 1415448: Experimental Crystal Structure Determination

Related Article: Hua Tian, Haijun Yang, Changjin Zhu, Hua Fu|2016|Scientific Reports|6|1|doi:10.1038/srep19931