De Haas-van Alphen Effect in Antiferromagnetic Chromium

Abstract

Cooling chromium through the Néel temperature in a magnetic field Hc alters the magnetic symmetry. The dH-vA amplitudes, but not the frequencies, change with increasing cooling field so as to reduce the symmetry from fourfold to twofold, the changes reaching saturation at cooling field Hs. For several crystals Hs falls in the range 15–25 kG, with an inverse correlation between purity and Hs. For the saturated case, the dH-vA oscillations exhibit the full tetragonal symmetry observed by Watts; furthermore, in several crystals cooled in zero field we have observed all the oscillations of the saturated case but with approximately cubic symmetry and no others. This is consistent with Hc aligning tetragonal domains each containing a single, constant amplitude magnetization wave along a 〈100〉 direction but inconsistent with Hc changing the relative amplitudes of three coexisting magnetization waves. Other crystals, including higher-purity samples, seem to exhibit a large residual tetragonality for Hc=0, suggesting that a perfect crystal of chromium might show full tetragonality even when cooled in zero field.