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Magnetoresistive random-access memory (MRAM) is poised to become a next-generation information storage device. Yet, many materials challenges remain unsolved before it can become a widely used memory storage solution. Among them, an urgent need is to identify a material system that is suitable for downscaling and is compatible with low-power logic applications. Self-assembled, vertically-aligned La_{2/3}Sr_{1/3}MnO_3:ZnO nanocomposites, in which La_{2/3}Sr_{1/3}MnO_3 (LSMO) matrix and ZnO nanopillars form an intertwined structure with coincident-site-matched growth occurring between the LSMO and ZnO vertical interfaces, may offer new MRAM applications by combining their superior electric, magnetic (B), and optical properties. In this paper, we show the results of electrical current induced magnetic hysteresis in magneto-resistance measurements in these nano-pillar composites. We observe that when the current level is low, for example, 1 uA, the magneto-resistance displays a linear, negative, non-hysteretic B field dependence. Surprisingly, when a large current is used, I > 10 uA, a hysteretic behavior is observed when the B field is swept in the up and down directions. This hysteresis weakens as the sample temperature is increased. A possible spin-valve mechanism related to this electrical current induced magnetic hysteresis is proposed and discussed., accepted to Phys. Rev. Materials

While pyrochlore iridate thin films are theoretically predicted to possess a variety of emergent topological properties, experimental verification of these predictions can be obstructed by the challenge in thin film growth. Here we report on the pulsed laser deposition and characterization of thin films of a representative pyrochlore compound Bi₂Ir₂O₇. The films were epitaxially grown on yttriastabilized zirconia substrates and have lattice constants that are a few percent larger than that of the bulk single crystals. The film composition shows a strong dependence on the oxygen partial pressure. Density-functional-theory calculations indicate the existence of BiIr antisite defects, qualitatively consistent with the high Bi: Ir ratio found in the films. Both Ir and Bi have oxidation states that are lower than their nominal values, suggesting the existence of oxygen deficiency. The iridate thin films show a variety of intriguing transport characteristics, including multiple charge carriers, logarithmic dependence of resistance on temperature, antilocalization corrections to conductance due to spin-orbit interactions, and linear positive magnetoresistance. We thank Professor J. Wang, Dr. Y. Wang, Prof. Y. Lan, Dr. C.-H. Chen and S. Cheema for fruitful discussions. S. X. Z. acknowledges start-up support from Indiana University (IU) College of Arts and Sciences. J. J. H. and Y. X. were supported for the transport measurements by the U.S. Department of Energy, Office of Basic Energy Sciences, Division of Materials Sciences and Engineering under award DOE DE-FG02-08ER46532. K.P. is grateful to John W. Villanova for creating the initial pyrochlore structure and to Denis Demchenko for an advice in computation of formation energy, and was supported by U.S. National Science Foundation DMR-1206354, San Diego Supercomputer Center (SDSC) Comet and Gordon under DMR060009N, and Advanced Research Computing at Virginia Tech. We thank the IU Nanoscale Characterization Facility for access to the scanning electron microscope. XPS instrument at Nanoscale Characterization Facility of IU Nanoscience Center was funded by NSF Award DMR MRI-1126394. The X-ray diffraction facilities at the IU Molecular Structure Center was supported by NSF Grant No. CHE-1048613. The work at Los Alamos National Laboratory was supported by the NNSA's Laboratory Directed Research and Development Program and was performed, in part, at the Center for Integrated Nanotechnologies, an Office of Science User Facility operated for the U.S. Department of Energy (DOE) Office of Science. Los Alamos National Laboratory, an affirmative action equal opportunity employer, is operated by Los Alamos National Security, LLC, for the National Nuclear Security Administration of the U.S. Department of Energy under contract DE-AC52-06NA25396.

We report the observation of field-induced magnetization of BiFeO3 (BFO) in an ultrathin BFO/La0.7Sr0.3MnO3 (LSMO) superlattice using polarized neutron reflectivity (PNR). Our PNR results indicate parallel alignment of magnetization across BFO/LSMO interfaces. The study showed an increase in average magnetization on increasing applied magnetic field at 10K. We observed a saturation magnetization of 110 \pm 15 kA/m (~0.8 {\mu}B/Fe) for ultrathin BFO layer (~2 unit cell) sandwiched between ultrathin LSMO layers (~ 2 unit cell), which is much higher than the canted moment (0.03 {\mu}B/Fe) in the bulk BFO. The macroscopic VSM results on superlattice clearly indicate superparamagnetic behavior typically observed in nanoparticles of manganites.

Using polarized neutron reflectometry (PNR), we observe an induced magnetization of 75$\pm$ 25 kA/m at 10 K in a La$_{0.7}$Sr$_{0.3}$MnO$_3$ (LSMO)/BiFeO$_3$ superlattice extending from the interface through several atomic layers of the BiFeO$_3$ (BFO). The induced magnetization in BFO is explained by density functional theory, where the size of bandgap of BFO plays an important role. Considering a classical exchange field between the LSMO and BFO layers, we further show that magnetization is expected to extend throughout the BFO, which provides a theoretical explanation for the results of the neutron scattering experiment., 5 pages, 4 figures, with Supplemental Materials. To appear in Physical Review Letters

We report the observation of a nonlinear terahertz response of split-ring resonator arrays made of high-temperature superconducting films. Intensity-dependent transmission measurements indicate that the resonance strength decreases dramatically (i.e. transient bleaching) and the resonance frequency shifts as the intensity is increased. Pump–probe measurements confirm this behaviour and reveal dynamics on the few-picosecond timescale., Los Alamos National Laboratory. Laboratory Directed Research and Development Program, United States. Office of Naval Research (Grant N00014-09-1-1103), National Science Foundation (U.S.) (American Competitiveness in Chemistry Fellowship 1041979)

High power THz pulses induce near transparency in superconductive YBCO thin films below the critical temperature. THz pump/THz probe measurements reveal a decay of the induced transparency on the time scale of a few picoseconds., United States. Office of Naval Research (Grant N00014-09-1-1103), National Science Foundation (U.S.) (American Competitiveness in Chemistry Fellowship 1041979), Los Alamos National Laboratory. Laboratory Directed Research and Development Program

An emerging area in condensed matter physics is the use of multilayered heterostructures to enhance ferroelectricity in complex oxides. Here, we demonstrate that optically pumping carriers across the interface between thin films of a ferroelectric (FE) insulator and a ferromagnetic metal can significantly enhance the FE polarization. The photoinduced FE state remains stable at low temperatures for over one day. This occurs through screening of the internal electric field by the photoexcited carriers, leading to a larger, more stable polarization state that may be suitable for applications in areas such as data and energy storage.

Since the discovery of carbon nanotubes in 1991 by Iijima, there has been great interest in creating long, continuous nanotubes for applications where their properties coupled with extended lengths will enable new technology developments. For example, ultralong nanotubes can be spun into fibres that are more than an order of magnitude stronger than any current structural material, allowing revolutionary advances in lightweight, high-strength applications. Long metallic nanotubes will enable new types of micro-electromechanical systems such as micro-electric motors, and can also act as a nanoconducting cable for wiring micro-electronic devices. Here we report the synthesis of 4-cm-long individual single-wall carbon nanotubes (SWNTs) at a high growth rate of 11 microm s(-1) by catalytic chemical vapour deposition. Our results suggest the possibility of growing SWNTs continuously without any apparent length limitation.

The low-frequency dielectric response of hole-doped insulators La_{2}Cu_{1-x}Li_{x}O_{4} and La_{2-x}Sr_{x}NiO_{4} shows a large dielectric constant \epsilon ^{'} at high temperature and a step-like drop by a factor of 100 at a material-dependent low temperature T_{f}. T_{f} increases with frequency and the dielectric response shows universal scaling in a Cole-Cole plot, suggesting that a charge glass state is realized both in the cuprates and in the nickelates., Comment: 5 pages, 4 figures

We present a comparative study of the angular dependent critical current density in YBa2Cu3O7 films deposited on IBAD MgO and on single crystal MgO and SrTiO3 substrates. We identify three angular regimes where pinning is dominated by different types of correlated and uncorrelated defects. We show that those regimes are present in all cases, indicating that the pinning mechanisms are the same, but their extension and characteristics are sample dependent, reflecting the quantitative differences in texture and defect density. In particular, the more defective nature of the films on IBAD turns into an advantage as it results in stronger vortex pinning, demonstrating that the critical current density of the films on single crystals is not an upper limit for the performance of the IBAD coated conductors., Comment: 14 pages, 3 figures. Submitted to APL