Origins of ferromagnetism and antiferromagnetism in Gd5Ge4

The total and partial density of states (DOS) of two polymorphic modifications of Gd5Ge4 show varying hybridization between the 5d states of Gd and the 4p states of Ge resulting in differences in the magnetism of the compound that are consistent with changes in the chemical bonding. The integrated numbers of electrons in the minority and majority bands differ substantially from one allotrope to another, showing different magnetic moments. A substantial decrease of indirect exchange interactions between 4f spins of specific Gd atoms, which is reflected in the decrease of 5d DOS and the 5d band splitting at the Fermi level, supports the antiferromagnetic ground state of Gd5Ge4. As follows from calculations of 4f-5d exchange interaction energies, total energy analysis of different spin configurations, and band energy analysis, short range interactions are ferromagnetic but long range antiferromagnetic coupling between Gd atoms prevails in the ground state allotrope of Gd5Ge4. On the other hand, only ferromagnetic coupling is found in the high field Gd5Ge4 structure