First-principles prediction of high Curie temperature for ferromagnetic bcc-Co and bcc-FeCo alloys and its relevance to tunneling magnetoresistance

The authors determine from first principles the Curie temperature TC for bulk Co in the hcp, fcc, bcc, and body-centered-tetragonal (bct) phases, for FeCo alloys, and for bcc and bct Fe. For bcc Co, TC=1420K is predicted. This would be the highest Curie temperature among the Co phases, suggesting that bcc-Co∕MgO∕bcc-Co tunnel junctions offer high magnetoresistance ratios even at room temperature. The Curie temperatures are calculated by mapping ab initio results to a Heisenberg model, which is solved by a Monte Carlo method.