Effect of exchange interaction in dumbbell Fe-Fe pairs on the curie temperature of the rhombohedral Gd2Fe17 phase

One of important problems of improving the magnetic properties of technologically promicing intermetallics R 2Fe17 (R is rare-earth metal) with high Fe contents is related to the increase in the Curie temperature T C. There is a hypothesis on the possibility of a marked increase in T C of the alloys, which can be achieved via the synthesis of systems characterized by pairs of atoms coupled by strong exchange interaction similar to that for Fe-Fe pairs situated in the so-called dumbbell position in the R 2Fe17 systems. In the present study, based on an example of the rhombohedral Gd2Fe17 phase, it was shown in terms of a classical nearest-neighbor spin Heisenberg model that changes in the exchange interaction for a dimer pair of dumbbell Fe-Fe atoms from zero to infinitely large lead to no more than 10% increase in T C. Thus, the creation of ferromagnetic systems characterized by dimers of magnetic atoms coupled by strong short-range exchange interaction, which, in this case, do not form an infinite magnetic cluster, cannot increase radically the Curie temperature T C.