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Dipolar field

Neelam Yadav, V P Panov, V Swaminathan, S P Sreenilayam, J K Vij, T S Perova, R Dhar, A Panov, D Rodriguez-Lojo, P J Stevenson
Infrared and dielectric spectroscopic techniques are used to investigate the characteristics of two chiral smectics, namely, 1,1,3,3,5,5,5-heptamethyltrisiloxane 1-[4^{'}-(undecyl-1-oxy)-4-biphenyl(S,S)-2-chloro-3-methylpentanoate] (MSi_{3}MR_{11}) and tricarbosilane-hexyloxy-benzoic acid (S)-4'-(1-methyl-hexyloxy)-3'-nitro-biphenyl-4-yl ester (W599). The orientational features and the field dependencies of the apparent tilt angle and the dichroic ratio for homogeneous planar-aligned samples were calculated from the absorbance profiles obtained at different temperatures especially in the smectic-A* phase of these liquid crystals...
June 2017: Physical Review. E
Héctor Sánchez-Esquivel, Karen Y Raygoza-Sánchez, Raúl Rangel-Rojo, Emanuele Gemo, Niccolò Michieli, Boris Kalinic, Jorge Alejandro Reyes-Esqueda, Tiziana Cesca, Giovanni Mattei
Ordered metallic nanoprism arrays have been proposed as novel and versatile systems for the observation of nonlinear effects such as nonlinear absorption. The study of the effect of the local field reinforcement on the fast optical third order nonlinear response around the Surface Plasmon Resonance is of great interest for many plasmonic applications. In this work, silver nanoprism arrays have been synthesized by the nanosphere lithography method. A low repetition rate tunable picosecond laser source was used to study the irradiance and wavelength dependence of the nonlinear absorption properties around the dipolar and quadrupolar resonances of the nanoarray with the use of the z-scan technique...
July 13, 2017: Scientific Reports
Alexander J Grutter, Kathryn L Krycka, Elena V Tartakovskaya, Julie A Borchers, K Sai Madhukar Reddy, Eduardo Ortega, Arturo Ponce, Bethanie J H Stadler
The first comprehensive three-dimensional picture of magnetic ordering in high-density arrays of segmented FeGa/Cu nanowires is experimentally realized through the application of polarized small angle neutron scattering. The competing energetics of dipolar interactions, shape anisotropy, and Zeeman energy in concert stabilize a highly tunable spin structure which depends heavily on the applied field and sample geometry. Consequently, we observe ferromagnetic and antiferromagnetic interactions both among wires and between segments within individual wires...
July 12, 2017: ACS Nano
Bidhan Hazra, Kamalika Das, Manabendra Chandra
The structure and morphology of nanomateials strongly influence their nonlinear optical properties. In this work, we report a systematic investigation of second order nonlinear optical responses and their structural dependencies in the case of a plasmonically hybrid nanostructure, hollow gold nanoprisms (HGNs). The first hyperpolarizabilities (β) of the HGNs have been measured using the two-photon Rayleigh scattering (TPRS) technique. The measured hyperpolarizability values are extremely large for the HGNs, larger than those for gold nanospheres or gold nanorods with similar size and surface area...
July 5, 2017: Physical Chemistry Chemical Physics: PCCP
Martin D Gelenter, Tuo Wang, Shu-Yu Liao, Hugh O'Neill, Mei Hong
Site-specific determination of molecular motion and water accessibility by indirect detection of (2)H NMR spectra has advantages over dipolar-coupling based techniques due to the large quadrupolar couplings and the ensuing high angular resolution. Recently, a Rotor Echo Short Pulse IRrAdiaTION mediated cross polarization ((RESPIRATION)CP) technique was developed, which allowed efficient transfer of (2)H magnetization to (13)C at moderate (2)H radiofrequency field strengths available on most commercial MAS probes...
July 3, 2017: Journal of Biomolecular NMR
Johannes Hellwagner, Kshama Sharma, Kong Ooi Tan, Johannes J Wittmann, Beat H Meier, P K Madhu, Matthias Ernst
Pulse imperfections like pulse transients and radio-frequency field maladjustment or inhomogeneity are the main sources of performance degradation and limited reproducibility in solid-state nuclear magnetic resonance experiments. We quantitatively analyze the influence of such imperfections on the performance of symmetry-based pulse sequences and describe how they can be compensated. Based on a triple-mode Floquet analysis, we develop a theoretical description of symmetry-based dipolar recoupling sequences, in particular, R264(11), calculating first- and second-order effective Hamiltonians using real pulse shapes...
June 28, 2017: Journal of Chemical Physics
Mukul G Jain, G Rajalakshmi, Asif Equbal, Kaustubh R Mote, Vipin Agarwal, P K Madhu
Rotational-Echo DOuble-Resonance (REDOR) is a versatile experiment for measuring internuclear distance between two heteronuclear spins in solid-state NMR. At slow to intermediate magic-angle spinning (MAS) frequencies, the measurement of distances between strongly coupled spins is challenging due to rapid dephasing of magnetisation. This problem can be remedied by employing the pulse-shifted version of REDOR known as Shifted-REDOR (S-REDOR) that scales down the recoupled dipolar coupling. In this study, we propose a new variant of the REDOR sequence where the positions of the π pulses are determined by a sine-squared function...
June 28, 2017: Journal of Chemical Physics
Zdeněk Janů, František Soukup
We show a continuous reading superconducting quantum interference detector magnetometer used to measure the magnetic moment of small samples of materials as a function of an applied magnetic field, temperature, and time. A sample is held stationary while the magnetic field and sample temperature may be varied continuously in an arbitrary way, determined by the user. The applied field range is ±25 mT and the temperature range is 4.2-150 K. The advantage of a stationary sample technique is that the sample is not exposed to variations in the magnetic field or temperature, which may set in when the sample is moving...
June 2017: Review of Scientific Instruments
Yi Li, Xavier de Milly, Flavio Abreu Araujo, Olivier Klein, Vincent Cros, Julie Grollier, Grégoire de Loubens
Phase coupling between auto-oscillators is central for achieving coherent responses such as synchronization. Here we present an experimental approach to probe it in the case of two dipolarly coupled spin-torque vortex nano-oscillators using an external microwave field. By phase locking one oscillator to the external source, we observe frequency pulling on the second oscillator. From coupled phase equations we show analytically that this frequency pulling results from concerted actions of oscillator-oscillator and source-oscillator couplings...
June 16, 2017: Physical Review Letters
A Orlova, E L Green, J M Law, D I Gorbunov, G Chanda, S Krämer, M Horvatić, R K Kremer, J Wosnitza, G L J A Rikken
We report a ^{51}V nuclear magnetic resonance investigation of the frustrated spin-1/2 chain compound LiCuVO_{4}, performed in pulsed magnetic fields and focused on high-field phases up to 56 T. For the crystal orientations H∥c and H∥b, we find a narrow field region just below the magnetic saturation where the local magnetization remains uniform and homogeneous, while its value is field dependent. This behavior is the first microscopic signature of the spin-nematic state, breaking spin-rotation symmetry without generating any transverse dipolar order, and is consistent with theoretical predictions for the LiCuVO_{4} compound...
June 16, 2017: Physical Review Letters
Li Zhang, Yi-Quan Zhang, Peng Zhang, Lang Zhao, Mei Guo, Jinkui Tang
As the simplest entity carrying intramolecular magnetic interactions, a dinuclear lanthanide complex serves as a model to investigate the effects of magnetic interactions on relaxation of magnetization, and importantly, it proves to be an efficient method to obtain robust single-molecule magnets via improving the communication between lanthanide centers. Here, three Dy2 complexes (1, 2, 3) with a similar structural motif, namely, [Dy2(HL)2(NO3)2(CH3CN)2]·2CH3CN (1), [Dy2(HL)2(NO3)2(DMF)2]·2H2O (2), and Dy2(HL)2(NO3)2(DMF)4 (3), were successfully assembled...
July 17, 2017: Inorganic Chemistry
Gauri M Mangalgiri, Phillip Manley, Wiebke Riedel, Martina Schmid
This work elaborates on the high scattering which dielectric nanorods exhibit and how it can be exploited to control light propagation across material interfaces. A detailed overview of how dielectric nanorods interact with light through a combination of dipolar scattering and leaky modes is performed via outward power flux calculations. We establish and account for design parameters that best result in light magnification owing to resonant behavior of nanorods. Impact of material parameters on scattering and their dispersion have been calculated to establish that low loss dielectric oxides like ZnO when nanostructured show excellent antenna like resonances which can be used to control light coupling and propagation...
June 27, 2017: Scientific Reports
I Dierking, M Heberle, M A Osipov, F Giesselmann
Dispersions of magnetic nanoparticles in a nematic liquid crystal were investigated as magnetic fields were applied in three different boundary condition geometries: (i) planar substrates and B ⊥ n, (ii) planar substrates and B ‖ n, and (iii) homeotropic substrates and B ⊥ n. Particle chaining is observed when a magnetic field is applied, with a periodicity perpendicular to the chains. Furthermore, linear chains are observed for the magnetic field applied perpendicular to the director, while zigzag chains are formed when the magnetic field direction is parallel to the director field...
June 22, 2017: Soft Matter
Dijana Zilic, Debdeep Maity, Mario Cetina, Kresimir Molcanov, Zoran Dzolic, Mirta Herak
The detailed single crystal electron spin resonance (ESR) analysis of oxalamide complexes with halogen-bridged copper dimers, supported by X-ray, magnetic susceptibility and powder ESR studies, is reported. Four complexes with two different ligands were synthesized: [CuLA(μ-X)]₂ and [CuLV(μ-X)]₂, where LA = N-(L-alanine methyl ester)-N'-((2-pyridine-2-yl)methyl)oxalamide and LV=N-(L-valine methyl ester)-N'-((2-pyridine-2-yl)methyl)oxalamide, while X=Cl or Br. X-ray analysis shows that geometry at each copper(II) ion is square pyramidal while two pyramids share one base-to-apex edge with parallel basal planes...
June 21, 2017: Chemphyschem: a European Journal of Chemical Physics and Physical Chemistry
Daniel Nohr, Bernd Paulus, Ryan Rodriguez, Asako Okafuji, Robert Bittl, Erik Schleicher, Stefan Weber
Light-generated short-lived radial pairs have been suggested to play pivotal roles in cryptochromes and photolyases. Chryptochromes are very probably involved in magnetic compass sensing in migratory birds and the magnetic-field-dependent behavior of insects. We examined photo-generated transient states in the cryptochrome of Drosophila melanogaster and in the structurally related DNA-repair enzyme Escherichia coli DNA photolyase. Using pulsed EPR spectroscopy, the exchange and dipolar contributions to the electron spin-spin interaction were determined in a straightforward and direct way...
June 19, 2017: Angewandte Chemie
Gabriel Cornilescu, René F Ramos Alvarenga, Thomas P Wyche, Tim S Bugni, Roberto R Gil, Claudia C Cornilescu, William M Westler, John L Markley, Charles D Schwieters
Establishing the relative configuration of a bioactive natural product represents the most challenging part in determining its structure. Residual dipolar couplings (RDCs) are sensitive probes of the relative spatial orientation of internuclear vectors. We adapted a force field structure calculation methodology to allow free sampling of both R and S configurations of the stereocenters of interest. The algorithm uses a floating alignment tensor in a simulated annealing protocol to identify the conformations and configurations that best fit experimental RDC and distance restraints (from NOE and J-coupling data)...
July 12, 2017: ACS Chemical Biology
L D C Jaubert, T Lin, T S Opel, P C W Holdsworth, M J P Gingras
Motivated by recent realizations of Dy_{2}Ti_{2}O_{7} and Ho_{2}Ti_{2}O_{7} spin ice thin films, and more generally by the physics of confined gauge fields, we study a model spin ice thin film with surfaces perpendicular to the [001] cubic axis. The resulting open boundaries make half of the bonds on the interfaces inequivalent. By tuning the strength of these inequivalent "orphan" bonds, dipolar interactions induce a surface ordering equivalent to a two-dimensional crystallization of magnetic surface charges...
May 19, 2017: Physical Review Letters
Amador García-Fuente, Andrés Vega
We present a theoretical approach, based on a density functional theoretic parametrization of a model Hamiltonian, that allows for the determination of the complete electronic 4f(n) and 4f(n-1)5d valence manifolds of a lanthanide ion impurity in different host lattices in an easy, fast and reliable way. The model accounts for the electrostatic interactions, ligand field splitting due to the surroundings of the impurity and spin-orbit coupling effects, which means that the parametrization is transferable to different ligand environments...
June 14, 2017: Physical Chemistry Chemical Physics: PCCP
Nicholas Cox, Anna Nalepa, Wolfgang Lubitz, Anton Savitsky
ELDOR-detected NMR (EDNMR) performed at higher magnetic fields is becoming an increasingly popular alternative to conventional ENDOR for the characterization of electron-nuclear hyperfine interactions owing to its enhanced sensitivity. However there are two key problems that limit its widespread adoption, with factors controlling: (i) lineshape distortions and; (ii) overall spectral resolution, still largely understood only at a qualitative level. Indeed highly anisotropic (dipolar) coupled species are particularly problematic in the EDNMR experiment...
July 2017: Journal of Magnetic Resonance
Philipp E Spindler, Philipp Schöps, Wolfgang Kallies, Steffen J Glaser, Thomas F Prisner
This article describes current uses of shaped pulses, generated by an arbitrary waveform generator, in the field of EPR spectroscopy. We show applications of sech/tanh and WURST pulses to dipolar spectroscopy, including new pulse schemes and procedures, and discuss the more general concept of optimum-control-based pulses for applications in EPR spectroscopy. The article also describes a procedure to correct for experimental imperfections, mostly introduced by the microwave resonator, and discusses further potential applications and limitations of such pulses...
July 2017: Journal of Magnetic Resonance
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