1,721,187 research outputs found
Molecular nanoMagnets for information technologies.
No full textMolecular nanoMagnets for information technologies
Magnetic behaviour of trioctahedral mica-2M1 occurring in amagnetic anomaly zone
No full textThis work relates the crystal chemistry and the magnetic behaviour of a trioctahedral mica (chemical formula: K0.90Na0.01Ca0.01Ba0.01&0.07)(Al0.05Fe2+ 1.20Mg1.38Ti0.32Mn0.01&0.04)(Al1.12Si2.88)O10 (F0.27OH1.27O0.46); unit cell parameters: a = 5.345(2), b = 9.261(4), c = 20.189(8) A; b =95.075(8)o) from Minto Block (Ungava peninsula, northern Quebec, Canada), a region characterized by high magnetic anomalies. Crystallographic and X-ray absorption spectroscopy data suggest a prevalentdivalent oxidation state for Fe and a disordered Fe2+ distribution in the two octahedralsites M1 and M2. The realpart of magnetic susceptibility shows two peaks at ~5.2 K and 120 K. However, asdemonstrated by AC magnetic susceptibility measurements, the origin of the two effects is different: the peak position of the first one (i.e. the effect revealed at 5.2 K) is frequency-dependent, thus suggesting a spin-glass like behaviour. The effect at 120 K can instead be attributed to the occurrence of diluted phases in mica matrix, such as Fe oxides
Potentialities of Molecular Nanomagnets for Information TechnologiesMolecular Magnets
No full textThe possibility of tailoring their functionalities at the molecular scale
makes Molecular nanoMagnets interesting for applications in Information Technolo-
gies where the race for extreme miniaturization will soon lead at requiring com-
ponents of few nanometers in size. Properties like the magnetic bistability or the
switchability by external stimuli actually allow to mimic, at the molecular scale, ba-
sic operations commonly used in computers while embedding magnetic molecules in
suitable electronic circuits allows the fabrication of novel spintronic devices. Even
more challenging is the control and the exploitation of quantum properties in molec-
ular spin clusters that may allow the encoding quantum information with molecules.
These concepts are substantiated by many achievements obtained in the recent years
and presented in this chapter along with some perspectives and next challenges for
the future
Decoherence induced by hyperfine interactions with nuclearspins in antiferromagnetic molecular rings
No full textDecoherence induced by hyperfine interactions with nuclearspins in antiferromagnetic molecular ringsMolecular magnets are effective few-level spin systems that allow for the observation of coherent dynamics. Electronic coherence is mainly limited by hyperfine interactions with nuclear spins. Here, we theoretically investigate the resulting inhomogeneous broadening and electron-nuclear entanglement: They take place on the nanosecond and microsecond time scales, respectively. Our microscopic description allows us to clarify the role played by the different chemical elements. The effect of spin echo and the dependence of decoherence on the magnetic field are also estimated. © 2008 The American Physical Society
Molecular Spins for Quantum Information Technologies
No full textTechnological challenges for quantum information technologies lead us to consider aspectsof molecular magnetism in a radically new perspective. The design of new derivatives and recentexperimental results on molecular nanomagnets are covered in this tutorial review through thekeyhole of basic concepts of quantum information, such as the control of decoherence andentanglement at the (supra-)molecular level
Some properties of the phonon spectra of transition metal disilicides VSi2, NbSi2, and TaSi2
No full textThe phonon spectra of metallic disilicides VSi2, NbSi2, and TaSi2 have been studied in detail by inelastic neutron scattering at 300 K and specific heat measurements between 10 K and 250 K. The specific heat calculated from the generalised phonon density of states extracted from neutron measurements is in good agreement with the measured lattice contribution to the specific heat. The properties of the phonon spectra are discussed in relation with other data reported for these isostructural and isoelectronic disilicides. (C) 2003 Elsevier Science Ltd. All rights reserved
Magnetic Anisotropy of Fe6 and Fe10 Molecular Rings by Cantilever Torque Magnetometry in High Magnetic Fields
No full textWe studied the magnetic anisotropy of 2 mol. magnets, Fe6 and Fe10, which comprise 6- and 10-membered rings of antiferromagnetically coupled Fe (III) ions (Si = 5/2), resp. Spin-flip transitions induced by the applied magnetic field (≤23 T) were investigated by cantilever torque magnetometry on microgram single crystals at very low temp. (down to 0.45 K). From the sharp, steplike variations of magnetic anisotropy at the transition fields, we detd. the singlet-triplet energy gap (Δ1) and the axial zero-field splitting parameter (D1) for the triplet state of Fe6 [Δ1 = 15.28(1) cm-1, D1 = 4.32(3) cm-1] and Fe10 [Δ1 = 4.479(4) cm-1, D1 = 2.24(2) cm-1]. By analyzing the addnl. steps obsd. in the Fe10 sample, we evaluated the ΔS and DS parameters for the total-spin multiplets with S ≤5. On the basis of our findings, we discuss the origin of magnetic anisotropy in Fe(III) rings and the application of torque magnetometry to the study of field-induced level crossing in mol. magnets
Estrazione , accelerazione, condizionamento di correnti di elettroni da plasma generato da catodo cavo di opportuna costruzione e loro impiego in apparecchiature e sistemi industriali di irraggiamento di elettroni
No full textEstrazione , accelerazione, condizionamento di correnti di elettroni da plasma generato da catodo cavo di opportuna costruzione e loro impiego in apparecchiature e sistemi industriali di irraggiamento di elettron
Valence tautomerism interconversion triggers transition to stable charge distribution in solid polymeric cobalt-polyoxolene complexes
No full textThe reaction of 3,3,3,3-tetramethyl-5,5,6,6-tetrahydroxy-1,1spiro-bis(indane), L, with cobalt salts inthe presence of diazine ligands affords polymeric derivatives of general formula[CoL(diazine)]∞·nH2O, L being coordinated as a mixed-valence SQ-Cat species. The bipiridyl ando-phenantroline derivatives have been characterised by means of magnetic, EPR and calorimetricmeasurements. The characterisation showed that both systems are obtained in a metastable chargedistribution, presumably trapped due to the class I character of the mixed valence form of the ligand.The occurrence of entropy-driven valence tautomeric interconversion induces the transition to the moststable charge distribution. The photomagnetic characterisation evidenced that valence tautomericprocess can be photoinduced and that the lifetime of the photoinduced metastable state, obtained inlow yield, is of ca. 2 × 105 s at 9 K
Low-temperature specific heat of Fe-6 and Fe-10 molecular magnets
No full textThe energy splitting of the low-lying levels has been investigated on two magnetic molecular clusters Fe-6 and Fe-10 by means of low-temperature zero-field specific-heat measurements. Significant deviations from the usual C similar to T-2 law were observed above the maximum of the main Schottky anomalies as a result of nonnegligible contributions from the excited spin states with S>1 and the estimated lattice contributions follow a phenomenological power law C/R similar to T-alpha with alpha-2.7 for both these compounds. The singlet-triplet energy gaps evaluated by the Schottky anomaly, T-0=19.2 K for Fe6 and 4.56 K for Fe-10, are smaller than what we can estimate by a simplified spin-Hamiltonian approach in the strong exchange approximation and using the energy levels obtained by the high-field magnetization and susceptibility measurements. This discrepancy asks for a more complex description of the low-lying states of these molecular clusters, beyond the strong exchange approximation. At very low temperatures T<<1 K, two low-energy Schottky anomalies were also observed in Fe-10, probably due to a small fraction of defected rings or to hyperfine contributions
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