Anomalous effect of magnetic breakdown on the oscillatory magnetization

Abstract

It is shown that the effect of magnetic breakdown on the oscillatory magnetization in metals can vary dramatically from that predicted by conventional theory. We report a detailed study of the amplitude of the de Haas–van Alphen (d. H. v. A.) magnetization of the magnetic breakdown β orbit in aluminium, which exhibits unexpected behaviour as a function of the magnitude and orientation of the magnetic field. Amplitude measurements have been made by using a sensitive field-modulation technique in which the interference, in particular, from quantum oscillations in the conductivity, could be reliably separated out. A generalized model for the effect of magnetic breakdown on the amplitude has been developed to explain these results. Calculations of the amplitude based on this model, with the use of breakdown fields deduced from an energy band structure including the spin–orbit interaction, are found to be in good agreement with experiment. The new model indicates that when breakdown is important, the d. H. v. A. frequency is not determined in general by an extremal cross section of the Fermi surface, as is conventionally assumed.