Search results for "Anisotropy"
showing 10 items of 912 documents
Modulation of the magnetic anisotropy of octahedral cobalt(ii) single-ion magnets by fine-tuning the axial coordination microenvironment
2019
Two mononuclear cobalt(II) complexes, with the formulas [Co(2,6-dfba)2(bpp)2(H2O)2]n (1) and [Co(2,6-dfba)2(bpe)2(H2O)2]n (2) (2,6-Hdfba = 2,6-difluorobenzoic acid, bpp = 1,3-bis(4-pyridyl)propane, bpe = 1,2-bis(4-pyridyl)ethylene), have been synthesized by combining Co(II) ions with benzoate derivatives and two homogeneous N-donor ligands, respectively. Constrained by the analogous CoN2O4 coordination spheres, the discretely hexa-coordinated Co(II) cores in both complexes display stretched octahedral geometries. The equatorial environments in both complexes are identical, whereas the axial sites are finely modulated by the different chemical natures of the terminal N-donor ligands. The com…
Tuning of an Optical Dimer Nanoantenna by Electrically Controlling Its Load Impedance
2009
International audience; Optical antennas are elementary units used to direct optical radiation to the nanoscale. Here we demonstrate an active control over individual antenna performances by an external electrical trigger. We find that by an in-plane command of an anisotropic load medium, the electromagnetic interaction between individual elements constituting an optical antenna can be controlled, resulting in a strong polarization and tuning response. An active command of the antenna is a prerequisite for directing light wave through the utilization of such a device.
ELECTRICAL-FIELD CONTROL OF MAGNETISM MEDIATED BY STRAIN IN Ni NANOSTRUCTURES FABRICATED ON PRE-POLED PMN–PT (011)
2013
We investigate the effects of piezoelectric-generated strain on the magnetization configuration of Ni nanostructures fabricated on pre-poled piezoelectric (011) [ Pb ( Mg 0.33 Nb 0.66) O 3]0.68–[ PbTiO 3]0.32 (PMN–PT) by high resolution X-ray microscopy. We observe a strong uniaxial anisotropy in the Ni nanostructures, due to the relaxation of the substrate following the deposition of the Ni . The anisotropy can be modified by the application of an electric field to the piezoelectric substrate (thus generating a piezoelectric strain in the system) through the magneto-elastic effect. By applying an electric field to the PMN–PT, the magnetization configuration in nanostructured Ni squares an…
Acoustic modes in metallic nanoparticles: atomistic versus elasticity modeling
2009
The validity of the linear elasticity theory is examined at the nanometer scale by investigating the vibrational properties of silver and gold nanoparticles whose diameters range from about 1.5 to 4 nm. Comparing the vibration modes calculated by elasticity theory and atomistic simulation based on the Embedded Atom Method, we first show that the anisotropy of the stiffness tensor in elastic calculation is essential to ensure a good agreement between elastic and atomistic models. Second, we illustrate the reduction of the number of vibration modes due to the diminution of the number of atoms when reducing the nanoparticles size. Finally, we exhibit a breakdown of the frequency-spectra scalin…
Nucleation in suspensions of anisotropic colloids
2005
We report Monte Carlo studies of liquid crystal nucleation in two types of anisotropic colloidal systems: hard rods and hard ellipsoids. In both cases we find that nucleation pathways differ strongly from the pathways in systems of spherical particles. Short hard rods show an effect of self-poisoning. This part of the article is based on a previous publication [T. Schilling, D. Frenkel, Self-poisoning of crystal nuclei in hard-rod liquids, Phys. Rev. Lett. 92 (2004) 085505]. When a crystallite forms, its surfaces are covered preferentially by rods which align perpendicular to the surface. Therefore subsequent growth is stunted. Hard, almost spherical ellipsoids can be compressed to very hig…
Texture analysis and optical anisotropy measurements of leukocytes for early diagnostics of diabetes mellitus
2004
DNA damage had been suggested to contribute to the pathogenesis of insulin dependent diabetes mellitus (IDDM). In this work we present a method for detection and discrimination of such DNA changes by means of analysis of light microscope images of anisotropically stained leukocytes nuclei. Several features of the images have been evaluated, including integrated optical density, degree of polarisation, and textural features. A genetic algorithm, coupled with a neural classifier, has been used to find the best features for identification of the pathology. Reported results indicate the best set is able to achieve an 83% correct classification ratio.
Analytical evaluation of chromatic dispersion in photonic crystal fibers
2005
We present a two-dimensional modal approach for the evaluation, in an analytical manner, of chromatic dispersion in any kind of optical fiber. It combines an iterative Fourier technique to compute the propagation constant at any fixed wavelength and an analytical procedure to calculate its derivatives. The proposed formulation takes into account the effective anisotropy of the interfaces and allows us to deal with microstructured fibers, in general, and specifically with realistic photonic crystal fibers (PCFs), including arbitrary spatial refractive-index distributions of dispersive and absorbing materials. This fast and accurate numerical technique is extremely useful for both analysis an…
Fiber Characterization Using Whispering Gallery Modes(Invited)
2019
Fiber whispering gallery modes (WGMs) are surface waves that propagate azimuthally along the outer surface of the fiber cladding. Those waves that are in phase every turn give rise to narrow resonances defined by the resonant wavelength and a high Q factor. The actual values of the resonant wavelengths depend on the radius and the refractive index of the fiber cladding, enabling the development of several fiber characterization techniques. In addition, the typical high Q factor of these resonances (Q > 106) provides the characterization techniques with a low detection limit. Here, we report the development of a technique for measuring temperature profiles along the optical fiber, which enab…
Ultrafast antiferromagnetic switching in NiO induced by spin transfer torques
2020
NiO is a prototypical antiferromagnet with a characteristic resonance frequency in the THz range. From atomistic spin dynamics simulations that take into account the crystallographic structure of NiO, and in particular a magnetic anisotropy respecting its symmetry, we describe antiferromagnetic switching at THz frequency by a spin transfer torque mechanism. Sub-picosecond S-state switching between the six allowed stable spin directions is found for reasonably achievable spin currents, like those generated by laser induced ultrafast demagnetization. A simple procedure for picosecond writing of a six-state memory is described, thus opening the possibility to speed up current logic of electron…
Anisotropic optical response of GaN and AlN nanowires.
2012
We present a theoretical study of the electronic structure and optical properties of free-standing GaN and AlN nanowires. We have implemented the empirical tight-binding method, with an orbital basis sp(3), that includes the spin-orbit interaction. The passivation of the dangling bonds at the free surfaces is also studied, together with the effects on the electronic structure of the nanowire. For both GaN and AlN nanowires, we have found a remarkable anisotropy of the optical absorption when the light-polarization changes, showing in the case of GaN a dependence on the nanowire size.