Differences in the Fermi Surface Topology of Paramagnetic and Antiferromagnetic Cr Studied by Positron Annihilation

Two-dimensional angular correlation of the positron annihilation radiation has been measured from Cr in its paramagnetic and antiferromagnetic phases, as well as from paramagnetic Cr 0.95 V 0.05 alloy. We report the first observation of a difference of the Fermi surface topology between the two phases. Using available band structure calculations, we interpret our results as the appearance of electron pockets at the point X of the Brillouin zone, when Cr goes to the paramagnetic phase.