Search results for "Magnetism"

Theoretical investigation of paramagnetic diazabutadiene gallium(III)-pnictogen complexes: insights into the interpretation and simulation of electro…

2005

The electronic structures and the spin density distributions of the paramagnetic gallium 1,4-diaza(1,3)butadiene (DAB) model systems [((t)Bu-DAB)Ga(I)[Pn(SiH3)2]]* and the related dipnictogen species [((t)Bu-DAB)Ga[Pn(SiH3)2]2]* (Pn = N, P, As) were studied using density functional theory. The calculations demonstrate that all systems share a qualitatively similar electronic structure and are primarily ligand-centered pi-radicals. The calculated electron paramagnetic resonance (EPR) hyperfine coupling constants (HFCCs) for these model systems were optimized using iterative methods and were used to create accurate spectral simulations of the parent radicals [((t)Bu-DAB)Ga(I)[Pn(SiMe3)2]]* (P…

Eksperimentālā fizika, 2. sējums: Elektrība. Magnetisms. Atombūve

1925

Absorption band at 7.6 eV induced by γ-irradiation in silica glasses

2001

Optical absorption of defects induced by γ-irradiation in both natural and synthetic silica is experimentally investigated in the vacuum-ultraviolet (UV) range. Our results show that γ-rays, in a dose range of 1000 Mrad, induce an absorption band centered at 7.6 eV, the so-called E band, whose growth kinetics is not related to γ-activated precursors but to defects of the glassy matrix directly induced via the breaking of Si–O bonds occurring under γ-irradiation. Moreover, we observe that γ-rays do not bleach the E band present in some silica samples before irradiation, so ruling out that the associated defects can be precursors of the paramagnetic E′ centers, also induced by γ-irradiation.

Magnetic order in UCu4+xAl8−x

1992

Abstract A neutron diffraction study has been performed on UCu4+xAl8−x. The compound was chosen as an example of a uranium-based system, which goes from a magnetically ordered state to a pure heavy-fermion state. In the range x = 0.25–1, UCu4+xAl8−x orders in a simple collinear antiferromagnetic structure. With increasing concentration of Cu, the ordering temperature decreases and moment compensation develops due to the increasing hybridization of the 5f electrons.

Creation of paramagnetic defects by gamma irradiation in amorphous silica

2000

An electron spin resonance (ESR) study of the defects induced by γ-rays in various types of natural and synthetic silica is reported. Three main structures were identified: the E′ center and two doublets with field splitting of 7.4 and 11.8 mT, respectively, both centered around the E′ center signal. Another structure partially overlapping the E′ center line was also detected, consisting in three peaks with a maximum field splitting of 1.36 mT. We have investigated the growth kinetics of these centers on increasing the y-ray accumulated dose. In all investigated materials the growth of E′ centers can be interpreted as caused by γ-activated conversion of one or more precursors. The 1.36 mT s…

Long-range magnetic order in the porous metal–organic framework Ni(pyrazine)[Pt(CN)4]

2017

A combined study involving DFT calculations, neutron scattering, heat capacity and magnetic measurements at very low temperatures demonstrates the long-range magnetic ordering of Ni(pyrazine)[Pt(CN)4] below 1.9 K, describing its antiferromagnetic spin arrangement. This compound belongs to the family of porous coordination polymers M(pyrazine)[Pt(CN)4] (M = divalent metal), renowned for showing interesting combinations of porosity and magnetic properties. The possibility of including long-range magnetic ordering, one of the most pursued functional properties, opens new perspectives for the multifunctionality of this class of compounds.

Cross-linked PEEK-WC proton exchange membrane for fuel cell

2009

Abstract The low cost proton exchange membrane was prepared by cross-linking water soluble sulfonated-sulfinated poly(oxa- p -phenylene-3,3-phthalido- p -phenylene-oxa- p -phenylene-oxy-phenylene) (SsPEEK-WC). The prepared cross-linked membrane became insoluble in water, and exhibited high proton conductivity, 2.9 × 10 −2  S/cm at room temperature. The proton conductivity was comparable with that of Nafion ® 117 membrane (6.2 × 10 −2  S/cm). The methanol permeability of the cross-linked membrane was 1.6 × 10 −7  cm 2 /s, much lower than that of Nafion ® 117 membrane.

Covalent-ionically cross-linked polyetheretherketone proton exchange membrane for direct methanol fuel cell

2010

Abstract In this paper, the proton exchange membrane prepared by covalent-ionically cross-linking water soluble sulfonated–sulfinated poly(oxa- p -phenylene-3,3-phthalido- p -phenylene-oxa- p -phenylene-oxy-phenylene) (SsPEEK-WC) is reported. Compared with covalent cross-linked PEEK-WC membrane, this covalent-ionically cross-linked PEEK-WC membrane exhibits extremely reduced water uptake and methanol permeability, but just slightly sacrificed proton conductivity. The proton conductivity of the covalent-ionically cross-linked PEEK-WC membrane reaches to 2.1 × 10 −2  S cm −1 at room temperature and 4.1 × 10 −2  S cm −1 at 80 °C. The methanol permeability is 1.3 × 10 −7  cm 2  s −1 , 10 times …

Effect of disorder produced by cationic vacancies at theBsites on the electronic properties of mixed valence manganites

1999

An alloy series of single-phased polycrystalline ${\mathrm{La}}_{1\ensuremath{-}x}{\mathrm{Na}}_{x}{\mathrm{MnO}}_{3+\mathrm{\ensuremath{\delta}}} (0l~xl~0.15)$ has been synthesized in order to study the effect of disorder on the electronic properties of mixed valence manganites. The synthetic variables allow one to maintain a constant proportion of ${\mathrm{Mn}}^{4+}$ in the samples $({\mathrm{Mn}}^{3+}{/\mathrm{M}\mathrm{n}}^{4+}=2.1\ifmmode\pm\else\textpm\fi{}0.2),$ while the similar size of ${\mathrm{La}}^{3+}$ and ${\mathrm{Na}}^{+}$ ions results in no appreciable change in the tolerance factor of the perovskite structure throughout the series. In this way, the sodium content x contro…

Current-induced domain wall motion in nanoscale ferromagnetic elements

2011

The manipulation of a magnetic domain wall (DW) by a spin polarized current in ferromagnetic nanowires has attracted tremendous interest during the last years due to fundamental questions in the fields of spin dependent transport phenomena and magnetization dynamics but also due to promising applications, such as DW based magnetic memory concepts and logic devices. We comprehensively review recent developments in the field of geometrically confined domain walls and in particular current induced DW dynamics. We focus on the influence of the magnetic and electronic transport properties of the materials on the spin transfer effect in DWs. After considering the different DW structures in ferrom…