Half-Metallic L21 Structures with (001) Planar Insertions
Abstract
A number of L21 phase alloys (composition X2YZ) are half-metallic. Although this structure is typically described in terms of an fcc Bravais lattice with a 4 atom basis, it can be viewed more simply as a variant of bcc or B2 in which planes of X2 alternate with planes of YZ along the 001 direction. Using ab-initio electronic structure calculations, we have investigated planar insertions along 001 into the L21 structure. For most scenarios, insertion of single or double atomic layers of Cr into Co2MnGe or Co2MnSi did not destroy the half-metallic property. One insertion of a Cr layer into Co2MnGe was observed to increase the gap. In fact, we observed that for a large number of insertions using various transition metals or combinations of transition metals and non-transition metals, the band gap in the minority channel at the Fermi energy remains. An ad hoc rule that seems to partially capture the tendency to form half-metals can be formulated as: "001 planar insertions that can plausibly yield 8 down spin electrons on the X2 layer and 4 down spin electrons on the YZ layer yield half-metals".