Muon spin relaxation measurements of CsC60, RbC60, KC60

Muon spin relaxation (μ⁺SR) measurements of CsC₆₀ and RbC₆₀ have revealed magnetic ordering at 20 K and 15 K respectively, with static internal fields at the muon site of \sim7 G for both samples. No magnetic ordering is seen in KC₆₀ down to 2.5 K. An apparent small increase in muon spin relaxation which had been seen at 70 K in RbC₆₀ is ascribed to an extrinsic effect, originating in muons which stopped in the aluminum sample holder. This revised version was published online in July 2006 with corrections to the Cover Date.     

Fullerene local order in Na2CsC60 by23Na NMR

We have investigated the alkali metal fulleride Na₂CsC₆₀ by²³Na nuclear magnetic resonance (NMR), The NMR line of the tetrahedral site is split below 170 K (T and T′ lines) similarly to the A₃C₆₀ compounds with A=Rb or K. The intensity fraction of the T′ line follows the same temperature dependence as the¹³C NMR line width. We have also found that the spectrum is independent of the cooling rate. Spin-echo double resonance measurements show that T and T′ sites are mingled on a microscopic scale. We propose that the different²³Na NMR lines correspond to different fullerene orientational environments of the tetrahedral alkaline site.     

Role of dynamic Jahn-Teller distortions in Na2C60 and Na2CsC60 studied by NMR

Through 13C NMR spin lattice relaxation ( T1) measurements in cubic Na2C60, we detect a gap in its electronic excitations, similar to that observed in tetragonal A4C60. This establishes that Jahn-Teller distortions (JTD) and strong electronic correlations must be considered to understand the behavior of even electron systems, regardless of the structure. Furthermore, in metallic Na2CsC60, a similar contribution to T1 is also detected for 13C and 133Cs NMR, implying the occurrence of excitations typical of JT distorted C( 2-)60 (or equivalently C( 4-)60). This supports the idea that dynamic JTD can induce attractive electronic interactions in odd electron systems.     

High-field ESR in the metallic fullerides RbC60 and CsC60

We discuss field-dependent electron spin resonance (ESR) experiments on the orthorhombic phase of RbC₆₀ and CsC₆₀. X-and W-band measurements have been performed to determine electronic scattering rates in the metallic temperature regime from 50 to 350 K. The insulating low-temperature phase (T < 50 K) has been investigated by X-, Q-, and W-band ESR, i.e., at 9, 34 and 95 GHz, in order to clarify whether collective resonance modes of a possibly magnetic ground state can be observed.     

Beltlike C(60)(-) electron spin density distribution in the organic ferromagnet TDAE-C(60)

The observed huge increase in the width of the (3C)NMR spectra of TDAE-C(0 )n the middle of the ferromagnetic phase at 10 K is due to a Jahn-Teller distortion of the C(60 )(-) which becomes visible in view of the resulting changes in the Fermi contact electron-(13)C NMR shifts. The shape of the (13)C spectra allows for a direct determination of the belt-like redistribution of the unpaired electron spin density on the C(60)(-) ions, which is responsible for the relatively high ferromagnetic transition temperature in this purely organic system.     

二维R-C60聚合物的核磁共振波谱研究

合成了二维rhombohedral(2D-R)相C60聚合物,对其固体核磁共振(NMR)波谱进行了详细的讨论。 13C固体核磁共振魔角谱(13C MAS NMR )上δ145附近的sp2杂化峰出现展宽并伴有边带,并且在δ73附近出现了一个相对较弱的新的峰。这表明通过[2+2]加环反应在邻近C60分子之间形成了sp3杂化共价键,使得C60分子球笼上出现了五个位置不等价的sp2杂化碳原子,导致位于145ppm附近的sp2杂化峰展宽。我们利用拟合分峰的方法得出了这五个不等价的碳原子的峰的位置,分别位于δ134.6、δ139.6、δ145.1、δ147.9 以及δ149.1,这五个不等价的碳原子数目上的比例关系和核磁共振曲线的积分面积吻合。     

二维R-C60聚合物的核磁共振波谱研究

合成了二维rhombohedral(2D-R)相C60聚合物,对其固体核磁共振(NMR)波谱进行了详细的讨论. 13C固体核磁共振魔角谱(13C MAS NMR )上δ145附近的sp2杂化峰出现展宽并伴有边带,并且在δ72附近出现了一个相对较弱的新的峰.这表明通过[2+2]加环反应在邻近C60分子之间形成了sp3杂化共价键,使得C60分子球笼上出现了五个位置不等价的sp2杂化碳原子,导致位于δ145附近的sp2杂化峰展宽.利用拟合分峰的方法得出了这五个不等价的碳原子的峰的位置,分别位于δ134.6、δ139.6、δ145.1、δ147.9 以及δ149.1,这五个不等价的碳原子数目上的比例关系和核磁共振曲线的积分面积吻合.     

On the spin density distribution in the benzyl radical

The decay function of the electric moment of a dielectric shell is calculated directly. It is shown that this function depends on the initial polarization of the shell, the value assumed by Glarum being correct if the shell was initially polarized by a uniform external field, that used by Fatuzzo and Mason being correct if the shell was initially polarized by a central dipole.     

87Rb NMR investigations on binary and ternary fullerene compounds: Rb3C60, K2RbC60 and Rb2CsC60

Results of¹³C MAS NMR and⁸⁷Rb NMR measurements on Rb₃C₆₀, K₂RbC₆₀ and Rb₂CsC₆₀ are presented. The⁸⁷Rb NMR spectra show generally the same characteristics as already reported by other authors. For the ternary compound the degree of site preferential order of the alkali metal ions agrees with the analysis of X-ray absorption data. Furthermore, in the room temperature⁸⁷Rb NMR spectra of all samples an additional broadened line is detected indicating that at least for the samples prepared from sublimed C₆₀ a considerable amount of the Rb ions is located on sites with symmetry lower than cubic.     

Electron conductive three-dimensional polymer of cuboidal C60

Single crystals of three-dimensional (3D) C60 polymer were prepared by the topotactic conversion of two-dimensional (2D) C60 polymer single crystals at a pressure of 15 GPa at 600 degrees C. The x-ray single crystal study revealed that the 3D C60 polymer crystallized in a body centered orthorhombic space group Immm, and spherical C60 monomer units were substantially deformed to rectangular parallelepiped (cuboidal) shapes, each unit being bonded to eight cuboidal C60 neighbors via [3 + 3] cycloaddition. The 3D C60 polymer was electron conductive, in contrast with the nonconductive behavior of 2D polymers.     

Polarized spin density distribution in the chromyl ethyleneglycolate anion

Electron spin resonance (E.S.R.) studies of the long-lived paramagnetic species formed in dichromate ethylene glycol solutions are presented. These results, together with detailed calculations of the electronic structure, indicate that a fairly long-range atom-to-atom spin polarization occurs, producing small negative spin densities at the distant protons.     

Electron spin resonance spectrum of trapped in a single crystal matrix

The radical , labelled with ¹³C in the position shown, has been prepared by X-irradiation of single crystals of . The ¹³C hyperfine coupling tensor of this radical confirms previous conclusions from a study of the corresponding unlabelled species that the electron is essentially localized on the carbon atom. At room temperature the methylene group undergoes rapid reorientation about the P-C bond while comparison of the ¹³C tensors at 300 K and 77 K suggests that the barrier to rotation has a strong two-fold component but contains intermediate minima.     

Electron density distribution in GaAs using MEM

Electron density distribution of GaAs is determined by means of the maximum entropy method (MEM) using reasonably good X-ray data collected at room temperature and 200 K. The bonding electron distributions are clearly visible in the MEM map and the mixed covalent-ionic character in GaAs is evidenced. The density distributions at 200 K show more condensed electronic clouds as compared to the room temperature map, preserving the trend in the bonding characters. The electron densities at the middle of the bond are 0.79 and 0.70 e/ų at 200 K and at room temperature, respectively. The refined harmonic thermal factors are in good agreement with the published values.     

Electron spin resonance studies at the phase transition in YbInCu4

In the intermetallic compound YbInCu₄ the Gd³⁺-ESR and the static susceptibility were measured in the temperature range 1.5K–300 K, i.e. both below and above the valence phase transition which occurs in this material at T_ph≈50 K. The Gd³⁺ resonance is mainly determined by exchange interaction of Gd³⁺ ions with fluctuating Yb³⁺ ions via conduction electrons (RKKY coupling) both below and above this transition. Arguments are presented that at low temperature YbInCu₄ is a dense Kondo system (mixed valent state).     

Ultrasonic attenuation in the transverse spin density wave phase of chromium

A strong hysteretic attenuation peak is seen when a polarizing field itH_p is applied perpendicular to both the longitudinal ultrasonic wavevector itq and the wavevector itQ of the transverse spin density wave (TSDW) in chromium, i.e., itH_p⊥itq⊥ itQ, but not when (itH_p∥itq)⊥itQ. This effect is discussed in relation to the various models for the configuration of the polarization that have been proposed to explain the anomalous attenuation seen in the TSDW phase for itq⊥itQ.     

Electron momentum density and phase transition in SrO

In this article, we present electron momentum density distribution and phase transition in SrO. The experimental values of momentum density have been measured using 5Ci ²⁴¹Am Compton spectrometer and analyzed using theoretical data obtained from the ab-initio linear combination of atomic orbitals method. The first-principles calculations of the total energy of SrO as a function of cell volume have also been carried out for the cubic rocksalt (B1) and cesium chloride (B2) phases. Several structural parameters, i.e. equilibrium lattice constant, transition pressure, bulk modulus, etc. of B1 and B2 phases have been calculated and compared with the previous investigations. We conclude that the stable phase of SrO is B1 and the phase transition from B1 to B2 occurs at 35.8?GPa.     

Electron spin echo at S-band: Nuclear modulations and decay in C60 powder

At S-band (≈ 3 GHz) the modulation amplitude of the Electron Spin Echo patterns is increased with respect to the amplitude at X-band: as a consequence, it is possible to reveal the presence of nuclei not detectable at X-band. In this paper the results obtained by running ESE experiments at S-band on a C₆₀ powder sample containing radicals are shown and discussed. The two- and three-pulse Electron Spin Echo patterns exhibit both¹³C modulation and proton modulation not detected at X-band. The experimental data are quantitatively analyzed by simulating the time-domain patterns and their Fourier transforms. It results that a noticeable amount of proton nuclei surrounds the intrinsic paramagnetic centers. On the basis of the analysis, a possible explanation of their existence is given.     

The spin density and the optical spectrum of CoCl2- 4

The CoCl^2- ₄ ion has been studied using ab initio methods at various levels of approximation (RHF, UHF, CI and MC SCF). The calculations have been performed both with and without the Madelung field from crystalline surroundings. One of the main purposes has been to investigate the spin density, and determine its dependence on both correlation and external fields. The spin density is found to be fairly dependent on correlation but rather independent of the surrounding crystal. The lower excited quartet states have been calculated using CI expansions based upon ground state RHF and MC SCF wavefunctions. The experimental spectrum is very well reproduced on the MC SCF/CI level, both with and without the Madelung field.     

Longitudinal NMR and spin states in the A-like phase of 3He in aerogel

It was found that two different spin states of the A-like phase can be obtained in an aerogel sample. In one of these states, we have observed the signal of the longitudinal NMR, while, in the other state, no trace of such a signal was found. The states also have different properties in transverse NMR experiments. A longitudinal NMR signal was also observed in the B-like phase of ³He in aerogel. The text was submitted by the authors in English.