Magnetic Breakdown, Fermi Surface, and Galvanomagnetic Properties in Antiferromagnetic Metals

The effect of spin-density waves (SDW) on the electronic properties and Fermi surface of antiferromagnetic metals is examined. When the superlattice due to SDW is incommensurable with a crystal lattice, the usual Brillouin-zone picture of the energy spectrum breaks down, and energy gaps appear at arbitrary points in k space. They are susceptible to a perturbative method of calculation which converges rapidly for usual cases and normal experimental conditions. Several model calculations are performed. They indicate that for Cr, complete magnetic breakdown of all energy gaps of third or higher order in the superlattice potential should be expected for magnetic fields of about 10 G or higher.The perturbation treatment is applied to existing calculations of the paramagnetic Fermi surface of Cr, and the results are compared with experiment. Qualitative agreement is obtained for the magnetoresistance and Hall-effect data. Detailed comparison with the de Haas-van Alphen data proves to be not very fruitful with the present accuracy of the band-structure calculations. Some conclusions regarding the Fermi surface can, however, be obtained from the experimental evidence.