Itinerant ferromagnetism and antiferromagnetism from the perspective of chemical bonding

The quantum chemical tool crystal orbital Hamilton population (COHP) has been used for the analysis of bonding within metallic systems to predict the tendency for ferromagnetic and antiferromagnetic order. In these materials, the preference of bonding interactions and avoidance of antibonding interactions is realized not by conventional Jahn-Teller/Peierls distortions but simply by rearranging the spin sublattices upon spontaneous spin polarization. In general, spin-restricted bonding analyses of itinerant metals with a tendency for ferromagnetic order (such as alpha-Fe, Co, and Ni) exhibit antibonding states at the Fermi level that disappear upon going ferromagnetic; within the elemental metals the onset of magnetism strengthens the metal-metal bond. A typical antiferromagnet (Cr) shows nonbonding states in the highest bands that remain almost untouched during spin polarization. This bonding classification of potential ferro- or antiferromagnets also holds for intermetallic alloys,and can be utilized for rational syntheses. The recipe is exemplified with the help of multinary iron/manganese rhodium. borides in which various adjustments of the Fermi level have been synthetically realized. (C) 2003 Wiley Periodicals, Inc.