Bulletin of the American Physical Society
2014 Annual Meeting of the Mid-Atlantic Section of the APS
Volume 59, Number 9
Friday–Sunday, October 3–5, 2014; University Park, Pennsylvania
Session H5: Thin Films and Oxides |
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Chair: Raj Kolagani, Towson University Room: Life Sciences Building 009 |
Sunday, October 5, 2014 9:00AM - 9:36AM |
H5.00001: Multiferroic Tunnel Junctions and ferroelectric control of spins Invited Speaker: Qi Li Multiferroic tunnel junctions, i.e. magnetic tunnel junctions with a ferroelectric barrier, have become one of the very promising approaches for new generation of multifunctional devices and electric control of spins for spintronics. A large tunneling electroresistance (TER) is very desirable for utilizing the devices for signal processing with an on-site magnetic memory. To enhance the TER, we have designed a bilayer tunneling barrier in which one layer is ferroelectric and the other interface layer is close to ferromagnetic metal to antiferromagnetic insulator phase transition. Ferroelectric polarization reversal induces the phase transition of the interface layer due to the charge doping effect of the interface layer to screen the ferroelectric polarization. The effect of ferroelectric driven interface phase transition on the TER effect has been tested in La$_{0.7}$Sr$_{0.3}$MnO$_3$/BaTiO$_3$/La$_{0.5}$Ca$_{0.5}$MnO$_3$/La$_{0.7}$Sr0.$_3$MnO$_3$ tunnel junctions where the La$_{0.5}$Ca$_{0.5}$MnO$_3$ is the interface phase transition layer. We have found that the TER has increased from $\sim$30\% (without La$_{0.5}$Ca$_{0.5}$MnO$_3$ layer) to 10,000\% (with the inserted interface layer).1 The mechanisms of such large enhancement of TER come from two sources: one is the metal to insulator transition of the La0.5Ca0.5MnO3 which effectively change the barrier width for the two polarization states and the other is the polarization driven magnetic phase transition of La$_{0.5}$Ca$_{0.5}$MnO$_3$ from ferromagnetic to antiferromagnetic state. The antiferromagnetic phase in the barrier acted as a spin valve for spin polarized tunneling current. The ferroelectric control of the interface magnetic states have been further confirmed in magnetic field dependence of the TER and magnetic second harmonic generation. Details of the experimental results and the comparison with first principles calculation will be discussed. The results have also shown that the tunneling magnetoresistance can be turned on and off with ferroelectric polarization reversal of the barrier. [Preview Abstract] |
Sunday, October 5, 2014 9:36AM - 9:48AM |
H5.00002: ABSTRACT WITHDRAWN |
Sunday, October 5, 2014 9:48AM - 10:00AM |
H5.00003: Synthesis, characterization and photo-catalytic activity of Au--ZnO heterostructured nano-pyramids Oshadha Ranasingha, Congjun Wang, Christopher Matranga, James P. Lewis Pyramid shaped ZnO nano crystals were grown on top of spherical shaped Au nanoparticles. The UV-VIS absorption spectra clearly showed 2 clear absorption peaks which correspond to the 1st exciton peak of the ZnO (359 nm) and surface plasmon resonance of the Au nanoparticles (521 nm). The ZnO was 25.9 nm in size in the pure sample and 20.5 nm in the Au-ZnO heterostructures. The Au nanoparticles are around 5-6 nm in Au-ZnO. XRD patterns confirmed the wurtzite hexagonal structure for the ZnO and cubic structure for the Au. According to the High Resolution TEM (HRTEM) images, single crystal ZnO with ZnO (002) lattice fringes can be observed. But Au can be identified as polycrystalline particles with different Au (111) facets. At the interface, there is a lattice expansion in both ZnO (002) and Au (111) planes. Also, XRD Rietveld analysis confirmed a 3 times higher strain in ZnO particles in Au-ZnO compared to the pure ZnO. Methylene blue dye degradation reactions were performed to evaluate the catalytic activity of the Au-ZnO, which showed a very high catalytic activity compared to the pure ZnO. [Preview Abstract] |
Sunday, October 5, 2014 10:00AM - 10:12AM |
H5.00004: Atomic Layer-by-layer Growth of Oxide Thin Films by Laser MBE Qingyu Lei, Guozhen Liu, Maryam Golalikhani, Dongyue Yang, Ke Chen, Alexander X. Gray, Dario Arena, Andrew Farrar, Dmitri Tenne, Suilin Shi, Fuqiang Huang, Xiaoxing Xi We have established a laser MBE-based atomic layer-by-layer thin film growth technique. By in-situ monitoring the reflection high-energy electron diffraction (RHEED) intensity, oxide binary compound targets, such as SrO, TiO$_{2}$, were ablated sequentially to assemble SrTiO$_{3}$ in an atomic layer-by-layer manner. Stoichiometry and crystal structures of the films are confirmed ex-situ by Rutherford backscattering spectrometry and x-ray diffraction. UV Raman spectroscopy was used to probe the symmetry breaking due to the cation off-stoichiometry. Highly accurate stoichiometry control as shown by reactive MBE has been demonstrated. Similarly, CaMnO$_{3}$ films were deposited by ablating CaO and MnO$_{2}$ targets separately. The strain states and electronic structure of the CaMnO$_{3}$ films on various substrates were studied via x-ray diffraction and polarization-dependent x-ray absorption spectroscopy. This atomic layer-by-layer growth technique has applications on the growth of a wide range of perovskite thin films and superlattices. [Preview Abstract] |
Sunday, October 5, 2014 10:12AM - 10:24AM |
H5.00005: Electronic structure and metal-insulator transition in LaNiO$_{3}$ ultrathin films grown on LaAlO$_{3}$ substrates from separate oxide targets using laser MBE Maryam Golalikhani, Qingyu Lei, Dongye Yang, Leila Kasaei, Pasquale Orgiani, Dario Arena, Alexander Gray, Xiaoxing Xi Here we report on a novel approach of growing ultrathin LaNiO$_{3}$ films on LaAlO$_{3}$ substrate one atomic layer at a time using laser MBE with La$_{2}$O$_{3}$ and NiO targets. Reflection high energy electron diffraction (RHEED) spot intensity was used as the main technique to control stoichiometry and growth rate of alternating atomic layers with both LaO and NiO$_{2}$ surface termination. We studied the change in the thickness-dependent electronic structure of LaNiO$_{3}$ films across the metal-insulator transition. The techniques used in this study were the combination of temperature-dependent transport measurements, x-ray absorption spectroscopy (XAS) and x-ray linear dichroism (XLD) at the Ni $L_{3,2}$ and O $K$ absorption edges. We will report on the effect of the growth technique on electronic structure of this material. [Preview Abstract] |
Sunday, October 5, 2014 10:24AM - 10:36AM |
H5.00006: Magnetic properties of hexagonal HoFeO$_{3}$ thin films Zhuyun Xiao, Xiao Wang, Yaohua Liu, Xiaoshan Xu, Wenbin Wang, David Keavney, X.M. Cheng Multiferroic materials exhibit multiple ferroic orders simultaneously and have potential applications in information technology. Hexagonal HoFeO$_{3}$ (h-HFO) is a promising candidate for a multiferroics with room temperature ferromagnetism because of the expected enhanced Fe moment due to the exchange interaction between magnetic Ho$^{3+}$ and Fe$^{3+}$ ions. We report study of magnetic properties of epitaxial (001) h-HFO thin films deposited on (111) yttria-stabilized zirconia substrates via laser molecular beam epitaxy. X-ray diffraction of h-HFO thin films shows a six-fold symmetry. X-ray magnetic circular dichroism (XMCD) spectra for the Fe L$_{2, 3}$ edges and Ho M$_{5}$ edge were measured with the magnetic field applied parallel to the x-ray propagation direction and 60$^{\circ}$ away from the film normal. Temperature dependence of the XMCD spectra shows ferromagnetic ordering of Fe$^{3+}$ ions up to 200 K and paramagnetic behavior for Ho$^{3+}$ ions above 10 K. The saturation magnetic moment for Fe$^{3+}$ is determined by the sum rules to be 0.26 $\mu_{B}$/Fe cation at 10 K and 0.064 $\mu_{B}$/Fe cation at 200 K, which is about 10 times larger than the reported saturation Fe$^{3+}$ magnetic moment in h-LuFeO$_{3}$. The SQUID magnetometer results agree with the XMCD results. [Preview Abstract] |
Sunday, October 5, 2014 10:36AM - 10:48AM |
H5.00007: Electronic properties of silver delafossite materials (AgB$_{1-x}$Fe$_{x}$O$_{2})$ using high-throughput calculations Gihan Panapitiya, James Lewis Delafossites are promising materials which can be used as photovoltaics or photocatalysts to reduce the CO$_{2}$ to viable products such as CH$_{4}$ and CH$_{3}$OH. In this work, we present a high-throughput computational study for three delafossite oxides of the form AgB$_{1-x}$Fe$_{x}$O$_{2}$ (For B $=$ Al,Ga,In), in search of candidate materials which can harness visible light. We explore the effect on optoelectronic properties of these materials when the B site is alloyed with Fe. A large number of structures are studied by varying the Fe doping percentage(x) from 0 to 0.05 and by choosing the impurity sites randomly. Statistical analysis is carried out to study the relative positions of the substituent atoms (Fe). We will discuss the structural trends and the optoelectronic properties of these materials to determine their viability in potential photelectrochemical or photovoltaic applications. [Preview Abstract] |
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