Calculated elastic constants and electronic and magnetic properties of bcc, fcc, and hcp Cr crystals and thin films

Abstract

In order to understand the phase stability and physical properties of artificial close-packed Cr films, we have performed electronic structure and total-energy calculations for Cr in bcc, fcc, and hcp structures based density functional theory with local-density approximation plus generalized gradient corrections. The calculated lattice and elastic constants of the antiferromagnetic bcc Cr are in good agreement with experiments. The lattice constants of fcc and hcp Cr determined from the total-energy-volume curves are close to that of the reported close-packed Cr thin films. However, the calculated elastic constants show that fcc Cr is unstable against any shear deformation while hcp Cr would be unstable against only symmetry-breaking lattice distortions. Based on these findings, it is argued that the recently observed ultrathin close-packed Cr films on hcp Co form a hcp structure, and that the thin Cr films deposited on Au (Ir) (111) reported in the early 1970's are unlikely to have a fcc structure. Comparison of the calculated and experimental x-ray absorption spectra also indicates the formation of a hcp Cr phase for close-packed Cr thin films on hcp Co. Though the density-of-states at the Fermi level of fcc and hcp Cr is large, no ferromagnetic state is found for these structures. No simple commensurate antiferromagnetic state is found for the fcc and hcp Cr either. The results of the same calculations performed for the (111) fcc ${\mathrm{Cr}}_{3}/\mathrm{hcp}$ ${\mathrm{Co}}_{6},$ hcp ${\mathrm{Cr}}_{3}/\mathrm{hcp}$ ${\mathrm{Co}}_{7},$ fcc (hcp) ${\mathrm{Cr}}_{3}/\mathrm{fcc}$ ${\mathrm{Cu}}_{6}$ (111) multilayers are also reported in order to see the effects of the interfaces.