Search results for "paramagnetism"
showing 10 items of 354 documents
Bleaching of optical activity induced by UV Laser exposure in natural silica
2004
We report experimental data on two types of natural silica, differing for their OH content, irradiated with UV photons (4.66 eV) from a pulsed Nd:YAG laser. Irradiation induces a reduction of the absorption band at 5.12eV and of the associated emissions at 3.14eV and 4.28eV, ascribed to twofold coordinated Ge (=Ge'') centers pre-existing in our samples. The bleaching is mainly due to the post-irradiation conversion of =Ge'' into the paramagnetic H(II) center via trapping of a H atom. Comparison with literature data points out the peculiarities of silica with a low Ge concentration as regards UV induced transformations.
Optical absorption induced by UV laser radiation in Ge-doped amorphous silica probed by in situ spectroscopy
2007
We studied the optical absorption induced by 4.7eV pulsed laser radiation on Ge-doped a-SiO2 synthesized by a sol-gel technique. The absorption spectra in the ultraviolet spectral range were measured during and after the end of irradiation with an in situ technique, evidencing the growth of an absorption signal whose profile is characterized by two main peaks near 4.5eV and 5.7eV and whose shape depends on time. Electron spin resonance measurements performed ex situ a few hours after the end of exposure permit to complete the information acquired by optical absorption by detection of the paramagnetic Ge(1) and Ge-E' centers laser-induced in the samples.
Microscopic origin of magnetic anisotropy in martensitic Ni2MnGa
2011
The microscopic origin of magnetic anisotropy in the shape memory alloy Ni${}_{2}$MnGa is investigated by means of x-ray magnetic circular dichroism in transmission mode. Field- and angle-dependent dichroism spectra of epitaxial Ni${}_{2}$MnGa(101)/MgO(001) films reveal pronounced differences for magnetization aligned parallel and perpendicular to the film plane. These differences are related to an anisotropy of the orbital magnetic moment in agreement with the observed out-of-plane magnetocrystalline anisotropy. The spectral variation of the x-ray absorption originates from changes in the spin-projected density of states when the magnetization vector is rotated from the easy to the hard ma…
Excitation Spectrum of a Linear Chain of Paramagnetic Atoms with Spin-Phonon Interaction
1967
The low-lying energy levels of a paramagnetic chain in the presence of spin-phonon interaction have been investigated. It is shown that there is no gap in the one-particle excitation spectrum.
Phonon Avalanche and Superradiance in Paramagnetic Relaxation
1979
New quantum equations for superradiance in extended systems are presented. The possibility of acoustic superradiant emission is discussed on the basis of these equations and a new condition is introduced for superradiance to prevail over incoherent phonon avalanche.
Strong-coupling phases of the spin-orbit-coupled spin-1 Bose-Hubbard chain: Odd-integer Mott lobes and helical magnetic phases
2017
We study the odd integer filled Mott phases of a spin-1 Bose-Hubbard chain and determine their fate in the presence of a Raman induced spin-orbit coupling which has been achieved in ultracold atomic gases; this system is described by a quantum spin-1 chain with a spiral magnetic field. The spiral magnetic field initially induces helical order with either ferromagnetic or dimer order parameters, giving rise to a spiral paramagnet at large field. The spiral ferromagnet-to-paramagnet phase transition is in a novel universality class, with critical exponents associated with the divergence of the correlation length $\nu \approx 2/3$ and the order parameter susceptibility $\gamma \approx 1/2$. We…
New BEDT-TTF/[Fe(C5O5)3]3- Hybrid System: Synthesis, Crystal Structure, and Physical Properties of a Chirality-Induced α Phase and a Novel Magnetic …
2007
The paramagnetic and chiral anion [Fe(C5O5)3]3- (C5O52-=croconate) has been combined with the organic donor BEDT-TTF (=ET=bis(ethylenedithio)tetrathiafulvalene) to synthesize a novel paramagnetic semiconductor with the first chirality-induced alpha phase, alpha-(BEDT-TTF)5[Fe(C5O5)3].5H2O (1), and one of the few known paramagnetic molecular metals, beta-(BEDT-TTF)5[Fe(C5O5)3].C6H5CN (2). Both compounds present layers of BEDT-TTF molecules, with the alpha or beta packing modes, alternating with layers containing the high-spin S=5/2 Fe(III) anions and solvent molecules. In the alpha phase, the alternation of the chiral [Fe(C5O5)3]3- anions along the direction perpendicular to the BEDT-TTF cha…
Rational design of a new class of heterobimetallic molecule-based magnets: Synthesis, crystal structures, and magnetic properties of oxamato-bridged …
2008
Abstract Two new series of oxamato-bridged heterobimetallic coordination networks of general formula Li5[Li3M2(mpba)3(H2O)6] · 31H2O [M = NiII (1a) and CoII (1b)] and Li2[Mn3M2(mpba)3(H2O)6] · 22H2O [M = NiII (2a) and CoII (2b)] have been prepared from the metal-mediated self-assembly of the hexakis(bidentate), triple-stranded dinickel(II) and dicobalt(II) complexes [M2(mpba)3]8− [mpba = meta-phenylenebis(oxamato)] with either monovalent lithium(I) or divalent manganese(II) ions respectively, in water. X-ray structural analyses of 1a and 1b show an anionic three-dimensional network formed by an infinite parallel array of oxamato-bridged Li 3 I M 2 II (M = Ni and Co) hexagonal layers, which …
A stable oxoverdazyl free radical: Structural and magnetic characterization
2006
Abstract The structure and magnetic properties (susceptibility and ESR) of the stable oxoverdazyl free radical 6-(4-acetamidophenyl)-1,4,5,6-tetrahydro-2,4-dimethyl-1,2,4,5-tetrazin-3(2H)-one are presented. The crystal structure consists of chains of parallel planar molecules running along the b-axis. These chains are formed by dimers with a ring-over-bond overlap and a significant offset between dimers, although with similar inter- and intradimer distances. The susceptibility measurements show that this compound is an S = 1/2 paramagnet with weak antiferromagnetic interactions. The magnetic susceptibility can be very well reproduced with an antiferromagnetic regular chain model with g = 2.…
Colloidal layers in magnetic fields and under shear flow
2005
The behaviour of colloidal mono- and bilayers in external magnetic fields and under shear is discussed and recent progress is summarized. Superparamagnetic colloidal particles form monolayers when they are confined to a air–water interface in a hanging water droplet. An external magnetic field allows us to tune the strength of the mutual dipole–dipole interaction between the colloids and the anisotropy of the interaction can be controlled by the tilt angle of the magnetic field relative to the surface normal of the air–water interface. For sufficiently large magnetic field strength crystalline monolayers are found. The role of fluctuations in these two-dimensional crystals is discussed. Fur…