New magnetic forms of C60 have been identified which occur in the rhombohedral polymer phase. The existence of previously reported ferromagnetic rhombohedral C60 is confirmed. This property has been shown to occur over a range of preparation temperatures at 9 GPa. The structure is shown to be crystalline in nature containing whole undamaged buckyballs. Formation of radicals is most likely due to thermally activated shearing of the bridging bond resulting in dangling bond formation. With increasing temperatures this process occurs in great enough numbers to trigger cage collapse and graphitization. The magnetically strongest sample was formed at 800 K, and has a saturated magnetization at 10 K, in fields above 3 kOe, of 0.045 emu g-1.

The complete spectrum of the double spinon excitation in the spin-Peierls system CuGeO 3 is mapped as a function of temperature for the first time. The spin dynamics of the lower boundary and the excitation continuum evolve quite differently. Moreover, the dimerization of the lattice produces a sharp excitation in the lower energy boundary at the edge of the Brillouin zone, as well as the well known spin-gap opening at the zone center. [S0031-9007(96)01457-3]

A continuum of magnetic states has been observed by neutron scattering from the spin-1 chain compound CsNiCl3 in its disordered gapped one-dimensional phase. Results using both triple-axis and time-of-flight spectrometers show that around the antiferromagnetic point Qc = pi, the continuum lies higher in energy than the Haldane gapped excitations. At 6 K the integrated intensity of the continuum is about 12(2)% of the total spectral weight. This result is considerably larger than the 1%-3% weight predicted by the nonlinear sigma model for the three-particle continuum.

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Well-defined phonons with strong anomalous ͑upward͒ dispersion are observed by inelastic neutron scattering in liquid para-H 2 at a temperature of 15.7 K. The damping, being very small for the low-Q phonons, increases with wave vector Q, and only broad features are observed for Qտ1 Å Ϫ1 . This behavior is shown to deviate strongly from results of molecular simulations of a fully classical analogue using a realistic potential.

We review the potential to develop sources for neutron scattering science and propose that a merger with the rapidly developing field of inertial fusion energy could provide a major step-change in performance. In stark contrast to developments in synchrotron and laser science, the past 40 years have seen only a factor of 10 increase in neutron source brightness. With the advent of thermonuclear ignition in the laboratory, coupled to innovative approaches in how this may be achieved, we calculate that a neutron source three orders of magnitude more powerful than any existing facility can be envisaged on a 20- to 30-year time scale. Such a leap in source power would transform neutron scattering science.

A combination of reactive force field molecular dynamics and hybrid-exchange density functional theory (DFT) generates a defective structure of Rh-C 60 possessing an inter-cage link. Hybrid-exchange DFT is used within periodic boundary conditions to investigate the long-range magnetic coupling between the resulting defects. Inelastic neutron scattering experiments highlight the presence of hydrogen chemically bonded to carbon in the magnetic samples. A simple spin model previously applied to studies of planar conjugated electron systems is used to illustrate the mechanism through which chemically bonded hydrogen leads to a ferromagnetic ground state for this system. The recent observation of high temperature ferromagnetism in carbon materials is of great interest both as it introduces a class of potentially highly tunable materials for use in magnetic devices and because it presents a major challenge to our current understanding of magnetism. At elevated pressures and temperatures cubic C 60 fullerenes form well ordered two-dimensional polymerized phases. Below 9 GPa three distinct phases occur, with orthorhombic, tetragonal ͑T͒ and rhombohedral (Rh) symmetries.1 Further heating of these phases beyond ϳ900 K results in the collapse of the C 60 cages and the formation of hard "graphitic" phases. The ferromagnetic phases occur close to this phase boundary.2,3 A remarkably high Curie temperature ͑T c ͒ of ϳ500 K was reported in initial studies, 3 with recent data indicating an even higher T c of ϳ820 K. 4 Magnetic force microscopy (MFM) measurements 5 and additional experimental evidence 3 imply that the magnetism is an intrinsic property of carbon and not due to metallic impurities such as iron.The experimental characterization of the magnetic phases has proven difficult and currently the detailed atomic structure is not known. In situ x-ray diffraction measurements reveal a thermally activated process which converts the Rh phase (Fig. 1) into the highly disordered graphite-like phase, which displays very broad Bragg peaks. 6 The detailed structure of the magnetic phase cannot be determined from this data. Transmission electron microscopy (TEM) reveals an apparently well ordered crystalline structure in which the C 60 cages are largely intact and still in a Rh-C 60 -like arrangement.2 MFM studies established that only ϳ30% of the material is magnetic with the magnetism occurring in well defined domains. 5 As the characterization of the magnetic phase is problematic, theoretical calculations have an important role to play in determining possible local geometries. A number of previous theoretical studies have addressed the origins of magnetism in nonplanar carbon systems. Tight-binding molecular dynamics and cluster ab initio calculations have recently been used to analyze a single C 60 cage with a carbon vacancy. 7 Density functional theory (DFT) calculations have been used to examine a fullerene molecule during the transition to a nanotube segment via a series of Stone-Wales transformations 8 and a fragment with n...

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