ELECTRONIC-STRUCTURE, ITINERANT MAGNETISM AND ORBITAL ORDERING OF K2NIF4-TYPE COMPOUNDS

We report on the first comprehensive theoretical study of the electronic, magnetic and structural properties of the quasi-two-dimensional magnetic insulators K2NiF4 and K2CuF4. Our investigations were carried out by means of electronic structure calculations based on density functional theory within the local density approximation, and led to full agreement with experiment with regard to many important ground-state properties. In particular they result in a correct description of the two-dimensional electronic dispersion, the insulating behaviour, the magnetic order and the structural distortions inherent in these compounds. We were also able to study the delicate interplay of all these properties. Furthermore we arrive at the conclusion that band theory is well suited to describe magnetic systems, which possess localized moments and serve as almost ideal candidates for the Heisenberg model.