Fyzikální ústav Akademie věd ČR

Seminář Středa, 9. září 2009 - 15:00 - 20:00

Přednášející: Patrick Bruno, European Synchrotron Radiation Facility, Grenoble, France
Místo: přednáškový sál Fyzikálního ústavu na Slovance
Pořadatelé: FZÚ AV ČR

Exchange interactions constitute the "glue" that couples the individual magnetic moments in a solid to build a macroscopic magnet. In metallic systems the exchange interactions are mediated by conduction electrons. The fermionic character of the electrons and the existence of a Fermi surface leads to a characteristic oscillatory dependence of exchange interactions with respect to the distance between magnetic moments. This oscillatory behaviour is best illustrated in the case of metallic multilayers. Once exchange interactions are known, they can be used to study the critical (Curie or Néel) temperature of magnetic materials. To this purpose, the complicated itinerant magnetic system is mapped onto a much simpler Heisenberg model. This approximation has proved very successful to calculate from first principles the critical temperatures of bulk ferromagnets and antiferromagnets, ferromagnetic ultrathin films, disordered magnetic alloys, magnetic semiconductors or Heusler alloys. In nanostructures, quantum interferences can be used to "engineer" exchange interactions. In this lecture, I shall review theoretical work carried out on this topic over the past two decades.