111 research outputs found
Exchange-torque-induced excitation of perpendicular standing spin waves in nanometer-thick YIG films
Spin waves in ferrimagnetic yttrium iron garnet (YIG) films with ultralow
magnetic damping are relevant for magnon-based spintronics and low-power
wave-like computing. The excitation frequency of spin waves in YIG is rather
low in weak external magnetic fields because of its small saturation
magnetization, which limits the potential of YIG films for high-frequency
applications. Here, we demonstrate how exchange-coupling to a CoFeB film
enables efficient excitation of high-frequency perpendicular standing spin
waves (PSSWs) in nanometer-thick (80 nm and 295 nm) YIG films using uniform
microwave magnetic fields. In the 295-nm-thick YIG film, we measure intense
PSSW modes up to 10th order. Strong hybridization between the PSSW modes and
the ferromagnetic resonance mode of CoFeB leads to characteristic anti-crossing
behavior in broadband spin-wave spectra. A dynamic exchange torque at the
YIG/CoFeB interface explains the excitation of PSSWs. The localized torque
originates from exchange coupling between two dissimilar magnetization
precessions in the YIG and CoFeB layers. As a consequence, spin waves are
emitted from the YIG/CoFeB interface and PSSWs form when their wave vector
matches the perpendicular confinement condition. PSSWs are not excited when the
exchange coupling between YIG and CoFeB is suppressed by a Ta spacer layer.
Micromagnetic simulations confirm the exchange-torque mechanism.Comment: 9 pages, 6 figure
Unconventional magnonic surface and interface states in layered ferromagnets
Electronic surface, interface and edge states are well-known concepts in low-dimensional solids and have already been utilised for practical applications. It is expected that magnons–the bosonic quasiparticles representing the magnetic excitations– shall also exhibit such exotic states. However, how these states are formed in layered magnetic structures is hitherto unknown. Here we bring the topic of magnonic surface and interface states in layered ferromagnets into discussion. We provide experimental examples of synthetic layered structures, supporting our discussions and show that these states can be tailored in artificially fabricated structures. We demonstrate that the magnonic surface or interface states may show peculiar features, including "standing” or "ultrafast” states. We argue that these states can drastically change their electronic and magnonic transport properties. In this way one can design layered ferromagnets which act as magnon conductor, semiconductor and insulator of specific states
Wideband Brillouin light scattering analysis of spin waves excited by a white-noise RF generator
Spin waves are studied intensively for their intriguing properties and
potential use in future technology platforms for the transfer and processing of
information and microwave signals. The development of devices and materials for
spin-wave systems requires a lot of measurement time and effort, and thus
increasing the measurement throughput by extending the instrumentation
capabilities is of the essence. In this letter, we report on a new and
straightforward approach to increase the measurement throughput by fully
exploiting the wideband detection nature of the Brillouin light scattering
technique in single-shot experiments using a white-noise RF generator.Comment: 5 pages + 3 supplementary pages, 4 figures, 3 supplementary figure
Construction of a series of vectors for high throughput cloning and expression screening of membrane proteins from Mycobacterium tuberculosis
<p>Abstract</p> <p>Background</p> <p>One of the major challenges for membrane protein structural genomics is establishing high-throughput cloning and expression screening methods to obtain enough purified protein in a homogeneous preparation for structural and functional studies. Here a series of ligation independent cloning based vectors were constructed to address this challenge.</p> <p>Results</p> <p>The feasibility of these vectors was tested with 41 putative membrane proteins from <it>Mycobacterium tuberculosis</it>. The efficiency for direct cloning of these target genes from PCR products was 95% (39/41). Over 40% of cloned genes were overexpressed in <it>Escherichia coli </it>BL21 (DE3)-RP codon plus strain in the first round of expression screening. For those proteins which showed no expression, three protein fusion partners were prepared and it was found that each of the target proteins could be overexpressed by at least one of these fusions, resulting in the overexpression of two thirds of the cloned genes.</p> <p>Conclusion</p> <p>This expression platform features high throughput cloning, high flexibility for different constructs, and high efficiency for membrane protein overexpression, and is expected to be useful in membrane protein structural and functional studies.</p
Direct Determination of Electron-Phonon Coupling Matrix Element in a Correlated System
High-resolution electron energy loss spectroscopy measurements have been
carried out on an optimally doped cuprate Bi2Sr2CaCu2O8+{\delta}. The
momentum-dependent linewidth and the dispersion of an A1 optical phonon are
obtained. Based on these data as well as the detailed knowledge of the
electronic structure from angle-resolved photoemission spectroscopy, we develop
a scheme to determine the full structure of electron-phonon coupling for a
specific phonon mode, thus providing a general method for directly resolving
the EPC matrix element in systems with anisotropic electronic structures
Mechanical and Electrical Properties of a CFETR CSMC Conductor under Transverse Mechanical Loadings
The central solenoid model coil (CSMC) project of the China Fusion Engineering Test Reactor was launched in 2014 to verify the technological feasibility of a large-scale superconducting magnet at the Institute of Plasma and Physics Chinese Academy of Sciences. The short twist pitch design recommended by CEA is chosen for the CSMC Nb3Sn cable-in-conduit conductors. In order to better understand the evolution of transport properties and coupling losses related to the effect of electromagnetic load cycles, the mechanical and electrical properties were measured and investigated employing a special cryogenic press facility for the transverse mechanical loadings. The results show that the transverse compression (dy) versus applied load force (Fy ) is different from first to subsequent loading cycles. This mechanical behavior can be interpreted by the combination of strands bending between the crossovers and strands deformation at the crossovers. The fitting relations of dy versus Fy are also presented. The evolution of interstrand contact resistance (Rc) in the cabling stages with cyclic history and pressure effects are discussed. In addition, a fitting relation of Rc versus Fy is presented based on a combination of strand's microsliding and copper matrix resistivity. A clear correlation between intrapetal resistance Rc and coupling loss is also found
Bacterial Communities in the Womb During Healthy Pregnancy
The idea that healthy uterine cavity is sterile is challenged nowadays. It is still debatable whether the bacteria present in the uterine cavity during pregnancy are residents or invaders. To reveal microbiome composition and its characteristics in the womb of pregnant women, 41 decidual tissue samples and 64 amniotic fluid samples were taken from pregnant Chinese women. DNA extraction was followed by pyrosequencing of the hypervariable V4 region of the 16S rDNA gene to characterize womb microbiome. Both types of samples had low diversity microbiome with Enterobacteriaceae being the dominant phylotypes at family level. To characterize the nature of colonization during pregnancy, the presence of endogenous biomass was confirmed by cultivation. Surprisingly, all of the 50 amniotic fluid samples studied were culture-negative, whereas 379 out of 1,832 placenta samples were culture-positive. Our results suggested that womb contained microbiome with low diversity. Culture-based investigation of amniotic fluid and placenta samples confirmed the presence of cultivable microorganisms in the placenta but not in amniotic fluid. Thus it suggests that bacterial colonization does occur during healthy pregnancy
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