Temperature dependent magnetic exchange interactions in the paramagnetic state of hcp Gd

We use the first-principles magnetic force theorem embodied in the Korringa-Kohn-Rostoker method to calculate pair magnetic exchange interactions in pure hcp Gd metal in the ferromagnetic as well as in the paramagnetic state with disordered local 4f-moments. It is found that the exchange interactions between the localized 4f-moments, in particular also distant ones, depend on the state of magnetic disorder. Such a dependence is a consequence of the electronic structure changes of the conduction band that mediates the interaction between the local moments. The magnetic ordering temperature has been calculated using a Monte-Carlo simulation technique and the results are compared with mean-field based studies. It is also shown that most important interactions between of nearest neighbors Gd 4f moments is essentially non RKKY in character