Magnetic structure in FeCr and FeCo

Abstract

The occurrence of magnetic phases in FeCr and FeCo in the CsCl structure has been studied by first-principles total-energy calculations with a sensitive and accurate method, using a four-atom unit cell. When both atoms in such binary compounds can be strongly magnetic, unusual structures are found. These materials have ferromagnetic (FM) and antiferromagnetic (AF) phases, but the equilibrium state for both is FM. However at 3% expansion of the lattice constant the ground state of FeCr becomes AF, whereas in FeCo the AF phase is never the ground state. The AF phase in both FeCr and FeCo has an unusual structure in that both the Fe and the Cr or Co sublattices are separately AF. In both the FM and AF phases at the equilibrium volume, the Fe moment is reduced in FeCr, but enhanced in FeCo from that in pure body-centered-cubic (bcc) Fe; also the Cr moment is increased from that in pure bcc Cr, while the Co moment is similar to the moment in hexagonal-dose-packed Co. In the FM phase of FeCr, but not in FeCo, the two Fe atoms in the four-atom unit cell have different moments, which have opposite signs at large volume. © 1999 American Institute of Physics.