Ab initio exchange interactions and magnetic properties of the Gd2Fe17 iron sublattice: Rhombohedral versus hexagonal phases

In the framework of the local spin-density approximation LSDA+U method electronic-structure and magnetic properties of the intermetallic compound Gd₂Fe₁₇ for both rhombohedral and hexagonal phases have been calculated. On top of that, ab initio exchange-interaction parameters within the Fe sublattice for all present nearest and next-nearest Fe ions have been obtained. It was found that for the first coordination sphere-exchange interaction is ferromagnetic. For the second coordination sphere-exchange interaction is observed to be weaker and of antiferromagnetic type. Employing the theoretical values of exchange parameters Curie temperatures T_C for the first as well as for the first and second coordination spheres of both hexagonal and rhombohedral phases of Gd₂Fe₁₇ within Weiss mean-field theory were estimated. Obtained values of T_C and its increase going from the hexagonal to rhombohedral crystal structure of Gd₂Fe₁₇ agree well with experiment. Also for both structures LSDA+U computed values of total magnetic moment agree well with experimental ones.