Alfvén-Wave Propagation and Damping in Pyrolytic and Single-Crystal Graphite

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Abstract
A systematic study of Alfvén-wavè propagation was carried out at 35 GHz in pyrolytic and single-crystal graphite by means of microwave transmission and reflection experiments at 4.2 and 77 K. The amplitude and phase of the propagating wave were measured independently, yielding values of the collision frequency and the effective-carrier mass density at 4.2 K. These values were in reasonable agreement with theoretical and previously reported experimental values, although there was some evidence that the collision time is magnetic field dependent. The measured mass densities for pyrolytic and single-crystal samples were the same within experimental error. Transmission measurements were carried out as a function of angle between the applied magnetic field and the direction of propagation, revealing a quasi-two-dimensional behavior of the mass density, characteristic of graphite. On the other hand, these measurements indicate little anistropy in the scattering rate. Experiments performed at 77 K yield a slightly higher value of the mass density, in agreement with the nonparabolic energy-band structure predicted by the Slonczewski—Weiss model. Very pronounced oscillatory structure observed in Alfvén-wave damping at 4.2 K in the case of single-crystal graphite is identified as Shubnikov—de Haas oscillations associated with both majority and minority carriers. The single-crystal data also revealed a small oscillation in the transmitted phase.