High-Field Galvanomagnetic Effects in Antiferromagnetic Chromium

Abstract

The effects of the antiferromagnetic spin-density wave on the Fermi surface of Cr have been investigated by measurement of the high-field galvanomagnetic properties of pure single-domain crystals of Cr (residual resistance ratios from 750 to 1760) in fields up to 200 kOe. The topological features of the Fermi surface are shown to be consistent with a single direction of open orbits parallel to Q, the wave vector of the spin-density wave, in agreement with the Lomer model of the Fermi surface. Magnetic breakdown through the superlattice energy gaps is observed in the 0-20-kOe range and again in the 60-200-kOe range for all orientations of H. Theoretical calculations by Falicov and Zuckermann suggest that the breakdown is probably occurring through the second- and first-order gaps. An estimate of the breakdown fields is made by comparing our results with the theoretical curves of Falicov and Sievert. The value of the energy gaps depends sensitively on the type of energy bands assumed, but a lower bound for first-order gaps is ∼0.05 eV. Measurements on multidomain crystals and the effects of a compressive stress are also discussed.