Electron interference oscillations and spin-density-wave energy gaps at the Fermi surface of antiferromagnetic chromium

A chain model incorporating the periodicity of the incommensurate spin density wave is used to describe the Fermi surface of antiferromagnetic chromium, and is found to give excellent semiquantitative agreement with much of the de Haas-van Alphen data obtained by other investigators. New experimental data are presented which confirm the anomalous features of the transverse magnetoresistance oscillations observed in antiferromagnetic chromium with the spin density wave vector Q[001], the current J[010], and the magnetic field H in the (010) plane near [100]. These anomalous features are explained with the help of the chain model as arising from a quantum interference effect in the transport of charge along open orbits in the direction of Q. Estimates are obtained from our experimental data for the size of the magnetic breakdown fields that characterize the interferometer trajectories, and hence for the energy gaps on the Fermi surface associated with the spin density wave. Previous theoretical estimates of the magnetic breakdown fields obtained by a perturbation calculation for a model of tight-binding s electrons are in poor agreement with our values.Work supported by the Natural Sciences and Engineering Research Council.