Exchange interactions in Gd 1− xCe xMn 2Ge 2 compounds

Abstract

The temperature dependence of the magnetisation and exchange interactions in Gd 1− x Ce x Mn 2Ge 2 compounds have been investigated by the molecular field theory based on two-sublattice model. The molecular field coefficients n MnMn, n GdMn and n GdGd, obeying the hierarchical relation n MnMn>| n GdMn|> n GdGd, were obtained by a numerical fitting process. The exchange coupling constants J MnMn, J GdMn and J GdGd have been calculated by using the molecular field coefficients. The Mn–Mn exchange energy increases with increasing x. J MnMn dominates the three kinds of interactions, implying that the magnetic interactions are dominated by the exchange between 3 d electrons. The theoretically calculated Curie temperatures were found to agree well with the experimental results. The exchange fields H Mn( T) and H Gd( T) were presented.