The control of non-equilibrium phenomena in complex solids is an important research frontier, enc... more The control of non-equilibrium phenomena in complex solids is an important research frontier, encompassing new effects like light induced superconductivity. Here, we show that coherent optical excitation of molecular vibrations in the organic conductor K 3 C 60 can induce a nonequilibrium state with the optical properties of a superconductor. A transient gap in the real part of the optical conductivity σ 1 (ω) and a lowfrequency divergence of the imaginary part σ 2 (ω) are measured for base temperatures far above equilibrium T c =20 K. These findings underscore the role of coherent light fields in inducing emergent order.
The family of superconducting fullerides (NH3)xNaK2C60 shows an anomalous correlation between Tc ... more The family of superconducting fullerides (NH3)xNaK2C60 shows an anomalous correlation between Tc and lattice parameter. To better understand the origin of this anomaly we have studied a representative x = 0.75 compound using SQUID magnetometry and µSR spectroscopy. The lower critical field Hc1, measured by the trapped magnetization method, is less than 1 G, a very small value as compared with that of other fullerides. Muon spin depolarization in the superconducting phase shows also quite small local field inhomogeneities, of the order of those arising from nuclear dipolar fields. On the other hand, the 40 T value for Hc2, as extracted from magnetometry data, is comparable to that of other fullerides. We show that these observations cannot be rationalized within the framework of the Ginzburg-Landau theory of superconductivity. Instead, the anomalous magnetic properties could be interpreted taking into account the role played by polaronic instabilities in this material.
We present results on the dynamics of the Li ions and of the C60 molecular units in Li12C60 obtai... more We present results on the dynamics of the Li ions and of the C60 molecular units in Li12C60 obtained by INS and QENS experiments performed on IN6 (at the Institut Laue-Langevin) covering the temperature range 150K to 600 K. The transition from the high temperature Fm3m to the Iow temperatur tetragonal structure of Li12C60 is accompanied by significant changes in
ABSTRACT The compound (NH3)xNaRb2C60 has been studied by SQUID magnetometry, and NMR. A double ir... more ABSTRACT The compound (NH3)xNaRb2C60 has been studied by SQUID magnetometry, and NMR. A double irradiation NMR experiment evidences a close distance between Na ions and ammonia, confirming the octahedral occupancy of this cluster which is usually observed in the ammonia intercalated fullerides. The Knight shift interaction of the ammonia protons with the conduction electrons is of pure anisotropic nature and is detected as a field dependent broadening of the NMR lines at low temperature. The recovery of the proton magnetisation follows a single exponential at all the investigated temperatures and fields. A Korringa behaviour is observed below 65 K and a clear Hebel–Slichter coherence peak is detected just below Tc. The Korringa relation does not hold and the Knight shift enhancement suggests the presence of a Coulomb repulsion.
The temperature dependence of the upper critical magnetic field H, 2 of the superconducting RbCs2... more The temperature dependence of the upper critical magnetic field H, 2 of the superconducting RbCs2C60 fullerene has been obtained. The value of H, 2(0) at zero temperature is estimated to be 17 T and the coherence length g(0)=4.4 nm. The lower critical field H"has been studied using three different methods. The H, &(T) dependence obtained from the procedures based on the deviation from perfect diamagnetism and on Bean s critical-state model has a positive curvature with decreasing temperature. It is shown from a high-field analysis that this saturationless dependence does not reflect the intrinsic H, & of the superconductor. The value of H, &(0) is estimated to be 5.5-8.1 mT and the penetration depth A, (0) = 300-370 nm.
In this report we combine synchrotron powder X-ray diffraction, 7Li nuclear magnetic resonance (N... more In this report we combine synchrotron powder X-ray diffraction, 7Li nuclear magnetic resonance (NMR) and electron paramagnetic resonance (EPR) experiments to study the structural evolution of Li4C60 and how its electronic ground state depends on the crystal symmetry. The compound in the two-dimensional polymer phase with mixed interfullerene bonding motifs is a band gap insulator. EPR however reveals the presence of intrinsic centers originating from broken C60-C60 bonds and local Li off-stoichiometry that create states in the band gap and account for the complex temperature dependence of the spin susceptibility as well as the residual temperature dependence of the 7Li NMR shift. Li+ ions are at low temperatures on the 7Li NMR timescale statically disordered. The observed 7Li NMR line narrowing T > 200 K is ascribed to the Li+ diffusion dynamics and above room temperature the polymer phase is already a good ionic conductor. Heating the sample to temperatures above ∼470 K results ...
We report on muon spin rotation (IISR) measurements of the internal magnetization in polycrystall... more We report on muon spin rotation (IISR) measurements of the internal magnetization in polycrystalline samples of the high Ts uperconductor YBa2Cu3O7_~. The mean value as well as the mean square deviation of the internal magnetic field seen by the muons undergo large variations with temperature. This effect shows a marked dependence on the magnetic history of the sample, which is what is expected of a glassy superconducting state.
We report on the extraordinary superionic conductivity in the fulleride polymer Li 4 C 60 , a cry... more We report on the extraordinary superionic conductivity in the fulleride polymer Li 4 C 60 , a crystalline material with no disorder. 7 Li, NMR, and dc frequency dependent conductivity show uncorrelated ionic hopping across small energy barriers (ÁE a $ 200 meV) and an ionic conductivity of 10 À2 S=cm at room temperature, higher than in ''standard'' ionic conductors. Ab initio calculations of the molecular structure find intrinsic unoccupied interstitial sites that can be filled by Li þ cations in stoichiometric Li 4 C 60 even at low temperatures. The low energy required for the occupation of these sites allows a sizable Li þ diffusion above 130 K. The results suggest novel application of lithium intercalated fullerides as electrodes in Li ions batteries.
We report an NMR and magnetometry study on the expanded intercalated fulleride Cs3C60 in both its... more We report an NMR and magnetometry study on the expanded intercalated fulleride Cs3C60 in both its A15 and face centered cubic structures. NMR allowed us to evidence that both exhibit a first-order Mott transition to a superconducting (SC) state, occuring at distinct critical pressures pc and temperatures Tc. Though the ground state magnetism of the Mott phases differs, their high T paramagnetic and SC properties are found similar, and the phase diagrams versus unit volume per C60 are superimposed. Thus, as expected for a strongly correlated system, the inter-ball distance is the relvevant parameter driving the electronic behavior and quantum transitions of these systems.
Li4C60, one of the best representatives of lithium intercalated fullerides, features a novel type... more Li4C60, one of the best representatives of lithium intercalated fullerides, features a novel type of 2D polymerization. Extensive investigations, including laboratory x-ray and synchrotron radiation diffraction, 13 C NMR, MAS and Raman spectroscopy, show a monoclinic I2/m structure, characterized by chains of [2+2]-cycloaddicted fullerenes, sideways connected by single CC bonds. This leads to the formation of polymeric layers, whose insulating nature, deduced from the NMR and Raman spectra, denotes the complete localization of the electrons involved in the covalent bonds.
The restoration of metallicity in the high-temperature, cubic phase of Li4C60 represents a remark... more The restoration of metallicity in the high-temperature, cubic phase of Li4C60 represents a remarkable feature for a member of the A4C60 family (A = alkali metal), invariably found to be insulators. Structural and resonance technique investigations on Li4C60 at T ¿ 600 K, show that its fcc structure is associated with a complete (4e −) charge transfer to C60 and a sparsely populated Fermi level. These findings not only emphasize the crucial role played by lattice symmetry in fulleride transport properties, but also re-dimension the role of Jahn-Teller effects in band structure determination.
ABSTRACT Muon spin resonance (μSR) is a powerful technique for investigating the local magnetic f... more ABSTRACT Muon spin resonance (μSR) is a powerful technique for investigating the local magnetic fields in materials through implanted muons. Here we report a μSR study of chemically produced thermally exfoliated graphene. Our results provide an experimental answer to the many theoretical investigations of magnetic properties of graphene. The observed muon spin precession is attributed to a localized muon-hydrogen nuclear dipolar interaction rather than to a hyperfine interaction with magnetic electrons. This proves the absence of magnetism in chemically produced thermally exfoliated graphene.
In this paper, we combine synchrotron powder x-ray diffraction, 7 Li nuclear magnetic resonance (... more In this paper, we combine synchrotron powder x-ray diffraction, 7 Li nuclear magnetic resonance (NMR) and electron paramagnetic resonance (EPR) experiments to study the structural evolution of Li 4 C 60 and how its electronic ground state depends on the crystal symmetry. The compound in the twodimensional polymer phase with mixed interfullerene bonding motifs is a band gap insulator. EPR, however, reveals the presence of intrinsic centers originating from broken C 60-C 60 bonds and local Li off-stoichiometry that create states in the band gap and account for the complex temperature dependence of the spin susceptibility as well as the residual temperature dependence of the 7 Li NMR shift. Li + ions are at low temperatures on the 7 Li NMR timescale statically disordered. The observed 7 Li NMR line narrowing T > 200 K is ascribed to the Li + diffusion dynamics and above room temperature the polymer phase is already a good ionic conductor. Heating the sample to temperatures above ∼470 K results in the gradual depolymerization to the metallic monomer fcc high temperature structure. The transformation is first order and polymer as well as monomer phases coexist over broad temperature interval (130 K).
performed the μSR experiments and data analyses, interpreted the results, prepared part of the sa... more performed the μSR experiments and data analyses, interpreted the results, prepared part of the samples, and performed the SQUID characterization. J.A.S. and M.C. synthesized part of the samples, performed elemental analysis and the Raman and microscopy investigations. O.V.Y. developed the theoretical model and performed first-principles calculations.
ABSTRACT N-(4-alkoxybenzylidene)4′-toluidines are a family of organic compounds which present a n... more ABSTRACT N-(4-alkoxybenzylidene)4′-toluidines are a family of organic compounds which present a nematic and (depending on the chain length) a smectic mesophase. We have performed proton spin echo measurements on some members of the family in these mesophases. N.M.R. spectra present well-defined structures that can be assigned to one of the two end methyl groups on the basis of phenomenological as well as analytical discussion, despite the large number of protons contributing to the total line shape. The order parameter derived from this analysis is compared with optical data on the same compounds.
We report here on the preparation and characterization of a fullerenium salt in the solid state, ... more We report here on the preparation and characterization of a fullerenium salt in the solid state, where the fullerene is in the 2+ oxidized state. To succeed in this long-standing challenge, we exploit the oxidizing power of one of the strongest Lewis acids, AsF 5. The weak nucleophilic character of its conjugate base is essential in stabilizing the fullerene dication in a crystal lattice. High-resolution structural analysis of this compound, with the formula C 60 (AsF 6) 2 , indicates that the highly reactive C 60 2+ units are arranged according to a novel 1D "zigzag" polymer structure. The molecules are connected by an alternating sequence of four-membered carbon rings ([2 + 2] cycloaddition) and single CC bonds. The long awaited high-T c superconductivity and magnetism, expected in a hole-doped C 60 compound, are replaced instead by a semiconducting behavior, quite probably originating from the reduced crystal and molecular symmetry upon polymerization. The small value of the energy gap (approximately 70 meV) suggests, nevertheless, the proximity of a metallic phase.
We have measured the zero-field muon spin relaxation (ZF p+SR) spectra of the quzi-ane-dimensiona... more We have measured the zero-field muon spin relaxation (ZF p+SR) spectra of the quzi-ane-dimensional fulleride conductor CsCa,,. Static magnetic order of a mndom nature develops gradually below about 30 K. The local field distribution at the muon site has a Gaussian shape with a width of 48.3(7) G at 2.8 K. Muon spin rotation (TF p+SR) measurements at an applied transverse field of 6 kG also show the onset of magnetic order in the same temperature range.
Protonatecl and deuterated samples of the dihydrofulleroid C,, H, [Suzuki T. Q. ("Ghan") Li, Khem... more Protonatecl and deuterated samples of the dihydrofulleroid C,, H, [Suzuki T. Q. ("Ghan") Li, Khemani K. C. and Wudl F., J. Am.-Chem. Sot. i14, 7301 (199i)], have been synthesized .and characterized bv "C. 'H, *H hiah resolution NMR. HPLC. TGA, DSC and mass snectrometrv. Its molecular dynamics have been s&died in the solid state with NMR and Quasi-elastic Neutron Scattering. The unitary interpretation of the results obtained from these two techniques gives a picture of the molecular reorientation in this system which is completely different from that observed in the rotor phase of c,, where the molecules are described to reorient isotropically, and should be compared to C,O
A representative rare earth doped fulleride, Eu 6 C 60 ; has been studied using several spectrosc... more A representative rare earth doped fulleride, Eu 6 C 60 ; has been studied using several spectroscopic and magnetometry techniques. We find that europium ions are present both in their magnetic bivalent state and nonmagnetic trivalent state. The Eu 2þ =Eu 3þ ratio seems to critically depend on sample preparation conditions. Muon relaxation rates show a large magnetic field distribution near the ordered phase, whereas 13 C NMR lineshapes at room temperature are consistent with dipolar field broadening (B100 G) from neighbouring Eu 2þ magnetic moments.
The control of non-equilibrium phenomena in complex solids is an important research frontier, enc... more The control of non-equilibrium phenomena in complex solids is an important research frontier, encompassing new effects like light induced superconductivity. Here, we show that coherent optical excitation of molecular vibrations in the organic conductor K 3 C 60 can induce a nonequilibrium state with the optical properties of a superconductor. A transient gap in the real part of the optical conductivity σ 1 (ω) and a lowfrequency divergence of the imaginary part σ 2 (ω) are measured for base temperatures far above equilibrium T c =20 K. These findings underscore the role of coherent light fields in inducing emergent order.
The family of superconducting fullerides (NH3)xNaK2C60 shows an anomalous correlation between Tc ... more The family of superconducting fullerides (NH3)xNaK2C60 shows an anomalous correlation between Tc and lattice parameter. To better understand the origin of this anomaly we have studied a representative x = 0.75 compound using SQUID magnetometry and µSR spectroscopy. The lower critical field Hc1, measured by the trapped magnetization method, is less than 1 G, a very small value as compared with that of other fullerides. Muon spin depolarization in the superconducting phase shows also quite small local field inhomogeneities, of the order of those arising from nuclear dipolar fields. On the other hand, the 40 T value for Hc2, as extracted from magnetometry data, is comparable to that of other fullerides. We show that these observations cannot be rationalized within the framework of the Ginzburg-Landau theory of superconductivity. Instead, the anomalous magnetic properties could be interpreted taking into account the role played by polaronic instabilities in this material.
We present results on the dynamics of the Li ions and of the C60 molecular units in Li12C60 obtai... more We present results on the dynamics of the Li ions and of the C60 molecular units in Li12C60 obtained by INS and QENS experiments performed on IN6 (at the Institut Laue-Langevin) covering the temperature range 150K to 600 K. The transition from the high temperature Fm3m to the Iow temperatur tetragonal structure of Li12C60 is accompanied by significant changes in
ABSTRACT The compound (NH3)xNaRb2C60 has been studied by SQUID magnetometry, and NMR. A double ir... more ABSTRACT The compound (NH3)xNaRb2C60 has been studied by SQUID magnetometry, and NMR. A double irradiation NMR experiment evidences a close distance between Na ions and ammonia, confirming the octahedral occupancy of this cluster which is usually observed in the ammonia intercalated fullerides. The Knight shift interaction of the ammonia protons with the conduction electrons is of pure anisotropic nature and is detected as a field dependent broadening of the NMR lines at low temperature. The recovery of the proton magnetisation follows a single exponential at all the investigated temperatures and fields. A Korringa behaviour is observed below 65 K and a clear Hebel–Slichter coherence peak is detected just below Tc. The Korringa relation does not hold and the Knight shift enhancement suggests the presence of a Coulomb repulsion.
The temperature dependence of the upper critical magnetic field H, 2 of the superconducting RbCs2... more The temperature dependence of the upper critical magnetic field H, 2 of the superconducting RbCs2C60 fullerene has been obtained. The value of H, 2(0) at zero temperature is estimated to be 17 T and the coherence length g(0)=4.4 nm. The lower critical field H"has been studied using three different methods. The H, &(T) dependence obtained from the procedures based on the deviation from perfect diamagnetism and on Bean s critical-state model has a positive curvature with decreasing temperature. It is shown from a high-field analysis that this saturationless dependence does not reflect the intrinsic H, & of the superconductor. The value of H, &(0) is estimated to be 5.5-8.1 mT and the penetration depth A, (0) = 300-370 nm.
In this report we combine synchrotron powder X-ray diffraction, 7Li nuclear magnetic resonance (N... more In this report we combine synchrotron powder X-ray diffraction, 7Li nuclear magnetic resonance (NMR) and electron paramagnetic resonance (EPR) experiments to study the structural evolution of Li4C60 and how its electronic ground state depends on the crystal symmetry. The compound in the two-dimensional polymer phase with mixed interfullerene bonding motifs is a band gap insulator. EPR however reveals the presence of intrinsic centers originating from broken C60-C60 bonds and local Li off-stoichiometry that create states in the band gap and account for the complex temperature dependence of the spin susceptibility as well as the residual temperature dependence of the 7Li NMR shift. Li+ ions are at low temperatures on the 7Li NMR timescale statically disordered. The observed 7Li NMR line narrowing T > 200 K is ascribed to the Li+ diffusion dynamics and above room temperature the polymer phase is already a good ionic conductor. Heating the sample to temperatures above ∼470 K results ...
We report on muon spin rotation (IISR) measurements of the internal magnetization in polycrystall... more We report on muon spin rotation (IISR) measurements of the internal magnetization in polycrystalline samples of the high Ts uperconductor YBa2Cu3O7_~. The mean value as well as the mean square deviation of the internal magnetic field seen by the muons undergo large variations with temperature. This effect shows a marked dependence on the magnetic history of the sample, which is what is expected of a glassy superconducting state.
We report on the extraordinary superionic conductivity in the fulleride polymer Li 4 C 60 , a cry... more We report on the extraordinary superionic conductivity in the fulleride polymer Li 4 C 60 , a crystalline material with no disorder. 7 Li, NMR, and dc frequency dependent conductivity show uncorrelated ionic hopping across small energy barriers (ÁE a $ 200 meV) and an ionic conductivity of 10 À2 S=cm at room temperature, higher than in ''standard'' ionic conductors. Ab initio calculations of the molecular structure find intrinsic unoccupied interstitial sites that can be filled by Li þ cations in stoichiometric Li 4 C 60 even at low temperatures. The low energy required for the occupation of these sites allows a sizable Li þ diffusion above 130 K. The results suggest novel application of lithium intercalated fullerides as electrodes in Li ions batteries.
We report an NMR and magnetometry study on the expanded intercalated fulleride Cs3C60 in both its... more We report an NMR and magnetometry study on the expanded intercalated fulleride Cs3C60 in both its A15 and face centered cubic structures. NMR allowed us to evidence that both exhibit a first-order Mott transition to a superconducting (SC) state, occuring at distinct critical pressures pc and temperatures Tc. Though the ground state magnetism of the Mott phases differs, their high T paramagnetic and SC properties are found similar, and the phase diagrams versus unit volume per C60 are superimposed. Thus, as expected for a strongly correlated system, the inter-ball distance is the relvevant parameter driving the electronic behavior and quantum transitions of these systems.
Li4C60, one of the best representatives of lithium intercalated fullerides, features a novel type... more Li4C60, one of the best representatives of lithium intercalated fullerides, features a novel type of 2D polymerization. Extensive investigations, including laboratory x-ray and synchrotron radiation diffraction, 13 C NMR, MAS and Raman spectroscopy, show a monoclinic I2/m structure, characterized by chains of [2+2]-cycloaddicted fullerenes, sideways connected by single CC bonds. This leads to the formation of polymeric layers, whose insulating nature, deduced from the NMR and Raman spectra, denotes the complete localization of the electrons involved in the covalent bonds.
The restoration of metallicity in the high-temperature, cubic phase of Li4C60 represents a remark... more The restoration of metallicity in the high-temperature, cubic phase of Li4C60 represents a remarkable feature for a member of the A4C60 family (A = alkali metal), invariably found to be insulators. Structural and resonance technique investigations on Li4C60 at T ¿ 600 K, show that its fcc structure is associated with a complete (4e −) charge transfer to C60 and a sparsely populated Fermi level. These findings not only emphasize the crucial role played by lattice symmetry in fulleride transport properties, but also re-dimension the role of Jahn-Teller effects in band structure determination.
ABSTRACT Muon spin resonance (μSR) is a powerful technique for investigating the local magnetic f... more ABSTRACT Muon spin resonance (μSR) is a powerful technique for investigating the local magnetic fields in materials through implanted muons. Here we report a μSR study of chemically produced thermally exfoliated graphene. Our results provide an experimental answer to the many theoretical investigations of magnetic properties of graphene. The observed muon spin precession is attributed to a localized muon-hydrogen nuclear dipolar interaction rather than to a hyperfine interaction with magnetic electrons. This proves the absence of magnetism in chemically produced thermally exfoliated graphene.
In this paper, we combine synchrotron powder x-ray diffraction, 7 Li nuclear magnetic resonance (... more In this paper, we combine synchrotron powder x-ray diffraction, 7 Li nuclear magnetic resonance (NMR) and electron paramagnetic resonance (EPR) experiments to study the structural evolution of Li 4 C 60 and how its electronic ground state depends on the crystal symmetry. The compound in the twodimensional polymer phase with mixed interfullerene bonding motifs is a band gap insulator. EPR, however, reveals the presence of intrinsic centers originating from broken C 60-C 60 bonds and local Li off-stoichiometry that create states in the band gap and account for the complex temperature dependence of the spin susceptibility as well as the residual temperature dependence of the 7 Li NMR shift. Li + ions are at low temperatures on the 7 Li NMR timescale statically disordered. The observed 7 Li NMR line narrowing T > 200 K is ascribed to the Li + diffusion dynamics and above room temperature the polymer phase is already a good ionic conductor. Heating the sample to temperatures above ∼470 K results in the gradual depolymerization to the metallic monomer fcc high temperature structure. The transformation is first order and polymer as well as monomer phases coexist over broad temperature interval (130 K).
performed the μSR experiments and data analyses, interpreted the results, prepared part of the sa... more performed the μSR experiments and data analyses, interpreted the results, prepared part of the samples, and performed the SQUID characterization. J.A.S. and M.C. synthesized part of the samples, performed elemental analysis and the Raman and microscopy investigations. O.V.Y. developed the theoretical model and performed first-principles calculations.
ABSTRACT N-(4-alkoxybenzylidene)4′-toluidines are a family of organic compounds which present a n... more ABSTRACT N-(4-alkoxybenzylidene)4′-toluidines are a family of organic compounds which present a nematic and (depending on the chain length) a smectic mesophase. We have performed proton spin echo measurements on some members of the family in these mesophases. N.M.R. spectra present well-defined structures that can be assigned to one of the two end methyl groups on the basis of phenomenological as well as analytical discussion, despite the large number of protons contributing to the total line shape. The order parameter derived from this analysis is compared with optical data on the same compounds.
We report here on the preparation and characterization of a fullerenium salt in the solid state, ... more We report here on the preparation and characterization of a fullerenium salt in the solid state, where the fullerene is in the 2+ oxidized state. To succeed in this long-standing challenge, we exploit the oxidizing power of one of the strongest Lewis acids, AsF 5. The weak nucleophilic character of its conjugate base is essential in stabilizing the fullerene dication in a crystal lattice. High-resolution structural analysis of this compound, with the formula C 60 (AsF 6) 2 , indicates that the highly reactive C 60 2+ units are arranged according to a novel 1D "zigzag" polymer structure. The molecules are connected by an alternating sequence of four-membered carbon rings ([2 + 2] cycloaddition) and single CC bonds. The long awaited high-T c superconductivity and magnetism, expected in a hole-doped C 60 compound, are replaced instead by a semiconducting behavior, quite probably originating from the reduced crystal and molecular symmetry upon polymerization. The small value of the energy gap (approximately 70 meV) suggests, nevertheless, the proximity of a metallic phase.
We have measured the zero-field muon spin relaxation (ZF p+SR) spectra of the quzi-ane-dimensiona... more We have measured the zero-field muon spin relaxation (ZF p+SR) spectra of the quzi-ane-dimensional fulleride conductor CsCa,,. Static magnetic order of a mndom nature develops gradually below about 30 K. The local field distribution at the muon site has a Gaussian shape with a width of 48.3(7) G at 2.8 K. Muon spin rotation (TF p+SR) measurements at an applied transverse field of 6 kG also show the onset of magnetic order in the same temperature range.
Protonatecl and deuterated samples of the dihydrofulleroid C,, H, [Suzuki T. Q. ("Ghan") Li, Khem... more Protonatecl and deuterated samples of the dihydrofulleroid C,, H, [Suzuki T. Q. ("Ghan") Li, Khemani K. C. and Wudl F., J. Am.-Chem. Sot. i14, 7301 (199i)], have been synthesized .and characterized bv "C. 'H, *H hiah resolution NMR. HPLC. TGA, DSC and mass snectrometrv. Its molecular dynamics have been s&died in the solid state with NMR and Quasi-elastic Neutron Scattering. The unitary interpretation of the results obtained from these two techniques gives a picture of the molecular reorientation in this system which is completely different from that observed in the rotor phase of c,, where the molecules are described to reorient isotropically, and should be compared to C,O
A representative rare earth doped fulleride, Eu 6 C 60 ; has been studied using several spectrosc... more A representative rare earth doped fulleride, Eu 6 C 60 ; has been studied using several spectroscopic and magnetometry techniques. We find that europium ions are present both in their magnetic bivalent state and nonmagnetic trivalent state. The Eu 2þ =Eu 3þ ratio seems to critically depend on sample preparation conditions. Muon relaxation rates show a large magnetic field distribution near the ordered phase, whereas 13 C NMR lineshapes at room temperature are consistent with dipolar field broadening (B100 G) from neighbouring Eu 2þ magnetic moments.
Il fullerene ei suoi derivati sono materiali molecolari di recente scoperta, che suscitano intere... more Il fullerene ei suoi derivati sono materiali molecolari di recente scoperta, che suscitano interesse nella comunita scientifica sia per l'affascinante varieta delle loro proprieta fisiche, che per le potenziali applicazioni tecnologiche.
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Papers by M. Riccò