FY2010 - Oak Ridge National Laboratory

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Director’s R&D Fund— Neutron Sciences Mission Relvance Arboviruses are major sources of human disease. Collectively, arboviruses are second only to malaria as a threat to global health. Worldwide, approximately 2.5 billion people are at risk of contracting this disease annually. Despite the enormous economic and medical impact of these agents, very few effective vaccines exist for their control. Therefore, this work will be of strong interest to the biomedical community. This work will also showcase the capabilities of the Spallation Neutron Source (SNS) and the High Flux Isotope Reactor (HFIR) and generate interest in neutron techniques among biomedical researchers in a manner that will drive cross-cutting science and expand the user community of these facilities. This work will also benefit agencies that are concerned with human health and veterinary medicine, such as the Department of Agriculture and the <strong>National</strong> Institutes of Health. Results and Accomplishments The ultimate goal of this project is to investigate the structures of viruses grown from two different sources (baby hamster kidney and insect cells) at pH 7.2 and 6.4 in order to track the virus structural changes in response to pH reduction. Low and neutral pH contrast series data were collected on the BIO- SANS (CG3) beamline at the HFIR in FY 2008 and 2009 for viruses grown from baby hamster kidney and insect cells. The neutral pH data have been analyzed using model-dependent and model-independent methods. In the model-independent method, Guinier approximation is used to determine the radius of gyration, Rg, of the virus particle. The model-dependent analysis using multiple concentric shells of different scattering length density and radius suggests that four shells are needed to fit the data satisfactorily. The analyses showed structural differences between the mammalian- and insect-cell-grown viruses. The results were published in the Journal of Virology. These small-angle neutron scattering experiments show that structural data of functional entities of large size and complexity can be collected and interpreted using the neutron scattering instruments at ORNL. We have applied the methodology developed in this project to another virus. Red Clover Necrotic Mosaic Virus can be used as nano-cargo for drug delivery. We are currently preparing a manuscript to describe its structural analysis by small-angle neutron scattering. These studies are critical as they illustrate the unique potential of neutron techniques for studying native virus particles, which will help attract the virology community to conduct structural studies using the SNS/HFIR instrument suite. Information Shared He, L., A. Piper, F. Meilleur, D. A. Myles, R. Hernandez, D. T. Brown, and W. T. Heller. 2010. “The structure of Sindbis virus produced from vertebrate and invertabrate hosts determined by small angle neutron scattering.” J. Virol. 84(10), 5270–5276. 05088 Inelastic Neutron Scattering from Magnetic Heterostructures Randy Fishman, J. Lee Robertson, Mark D. Lumsden, and Jian Shen Project Description Inelastic neutron scattering is the world’s most powerful tool to study the magnetic dynamics of solids. But only with the recent development of improved neutron optics and more powerful neutron sources 44
Director’s R&D Fund— Neutron Sciences such as the Spallation Neutron Source (SNS) has it become feasible to study the magnetic dynamics at interfaces and in confined geometries. We will develop the technique of inelastic neutron scattering from magnetic heterostructures consisting of alternating magnetic and nonmagnetic layers. To demonstrate the feasibility of this technique, we shall study Dy/Y and Ho/Y multilayers, which were chosen for the close lattice matches and the large dysprosium and holmium moments. Molecular-beamepitaxy will be used to fabricate heterostructures by repeating bilayers with roughly 45 Å of dysprosiumor holmium and 30 Å of yttrium. Magnetic characterization will be performed using the magnetism reflectometer at the SNS and inelastic measurements will be performed at the High Flux Isotope Reactor (HFIR). Simultaneously, we will develop the theory of inelastic neutron scattering from magnetic heterostructures by using a coupled Green’s function technique. Mission Relevance The development of an inelastic neutron scattering technique for the study of magnetic heterostructures will have wide-ranging implications for a variety of materials of technological and scientific interest. This new technique will enhance the potential applications of the SNS and HFIR, both of which are central to the DOE mission. Results and Accomplishments The synthesis group of Jian Shen was unable to produce high-quality samples of Dy/Y multilayers. As a result, the funding for this project was severely cut in FY 2009, with funds to support a theory postdoctoral researcher and little else. Despite this setback, we acquired high-quality Dy/Y samples from the group of Gary Mankey at the MINT center in Alabama. Some of Mankey’s materials costs were paid from the LDRD fund. The first samples arrived at ORNL in the summer of 2009. Elastic neutron scattering measurements confirmed the high quality of those samples. By stacking several multilayer samples on top of each other, inelastic measurements were able to obtain significant cross sections. While the inelastic results are promising, we are waiting for more samples from Mankey before beginning our analysis of these inelastic measurements in earnest. In our modeling efforts, we have tested a new Green’s function approach for the spin-wave dynamics on a generalized Villain model. That approach yields both the spin-wave frequencies and intensities. This work appeared in Journal of Physics: Condensed Matter. We have also used a spin-wave analysis to study the magnetic instabilities in aluminum-doped CuFeO 2 . The aluminum-doped material CuFe 1-x Al x O 2 (x > 0.016) exhibits a noncollinear and multiferroic magnetic ground state, which we have studied using Monte Carlo simulations. The results of that work appeared in two papers: one in Physical Review B and another in Physical Review Letters. More recently, we have studied the source of the net chirality observed in Dy/Y multilayers. Our results indicate that there are two mechanisms at work. First is the elastic torsion produced by a chiral deformation at the interface. Second are steps at the Dy–Y interface which can produce a net chirality of the dysprosium helix. The second mechanism may dominate after field cooling, explaining why the net chirality observed in Dy/Y multilayers can change sign. Control of chirality would have technological ramifications that are wide ranging. This work was published in the Rapid Communications Section of Physical Review B. We have also written a paper on the change in spin-wave dynamics from bulk dysprosium to the Dy/Y multilayer geometry. Discrete excitations that appear in an isolated dysprosium layer follow the bulk-like 45
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FY2010 - Oak Ridge National Laboratory

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