ELFT HÍRADÓ

[tcsaba AT eik.bme.hu]

                    M E G H Í V Ó - I N V I T A T I O N

       Seminar series of the Department of Theoretical Physics at the
             Budapest University of Technology and Economics


                                Attila Szilva
             (Department of Physics and Astronomy, Materials Theory
                           Uppsala University)

 Microscopic origin of Heisenberg and non-Heisenberg interatomic  
exchange in bcc Fe


 By means of first principles calculations we investigate the nature  
of exchange coupling in ferromagnetic bcc Fe on a microscopic level.  
Analyzing the basic electronic structure reveals a drastic difference  
between the 3d orbitals of Eg and T2g symmetries. The latter ones  
define the shape of the Fermi surface, while the former ones form  
weakly-interacting impurity levels. We demonstrate that, as a result  
of this, in Fe the T2g orbitals participate in exchange interactions,  
which are only weakly dependent on the configuration of the spin  
moments and thus can be classified as Heisenberg-like. These couplings  
are shown to be driven by Fermi surface nesting. In contrast, for the  
Eg states the Heisenberg picture breaks down, since the corresponding  
contribution to the exchange interactions is shown to strongly depend  
on the reference state they are extracted from. Our analysis of the  
nearest-neighbour coupling indicates that the interactions among Eg  
states are mainly proportional to the corresponding hopping integral  
and thus can be attributed to be of double-exchange origin.


Idöpont: 2015. december 18., 10:15
Helyszín: BME Fizikai Intézet, Elméleti Fizika Tanszék,
Budafoki út 8. F-épület, III lépcsöház, szemináriumi szoba



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