Oscillatory Magnetoresistance and Magnetic Breakdown in Antiferromagnetic Chromium

Abstract

Oscillations in the magnetoresistance, periodic in $\frac{1}{H}$, and associated with magnetic breakdown of the superlattice energy gaps in Cr, have been investigated in fields up to 200 kOe as a function of the field direction. Measurements were made at 4.2°K on single-domain single crystals having residual resistance ratios greater than 1000. Seven frequencies have been reduced and only one corresponds to a de Haas-van Alphen frequency observed by Graebner and Marcus at low fields where no magnetic breakdown occurs. Although the present knowledge of the band structure of Cr is inadequate to enable us to determine which pieces of the Fermi surface are breaking down, it can be argued that the breakdown must be associated with the hole surface, centered at $H$, which remains after the interaction that stabilizes the antiferromagnetic spin-density wave. A knowledge of the size and shape of this piece, together with the electron pockets at $X_1$, is critical to the determination of the actual orbits.