Pressure-Induced Decrease in the Curie Temperature of Gd{sub 2}Fe{sub 17}: LSDA+U Calculations
To explain the magnetic properties of advanced ferromagnetic intermetallic compounds of the R{sub 2}Fe{sub 17} (R is a rare-earth element) class, experimentalists often use the hypothesis of competition between ferromagnetic exchange and antiferromagnetic exchange between four types of the nearest iron atoms in nonequivalent lattice sites. For the rhombohedral Gd{sub 2}Fe{sub 17} ferromagnet, we calculate the magnetic moments of iron and gadolinium ions, the parameters of exchange between Fe atoms, and Curie temperature T{sub C} at a zero pressure and during hydrostatic lattice compression. The magnetic moment of the unit cell of Gd{sub 2}Fe{sub 17} is shown to decrease under pressure, and this decrease is almost completely associated with a decrease in the magnetic moments of Fe rather than Gd ions, the pressure dependence of the magnetic moments of which is weaker by an order of magnitude. In contrast to the hypothesis regarding the competition of exchange interactions between different kinds of Fe atoms, the parameters of exchange between the nearest iron atoms in different crystallographic sites are found to be positive ferromagnetic (at a zero pressure and during compression), and a ferromagnetic character of interaction is shown to remain unchanged under pressure even for Fe atoms in the so-called dumbbell sites with the nearest interatomic distances. The Curie temperature T{sub C} of Gd{sub 2}Fe{sub 17} is shown to decrease with increasing pressure. The changes in the exchange parameters and the magnetic moments of Gd{sub 2}Fe{sub 17} during compression are found to be mainly related to a change in the position of energy spectrum branches with respect to each other and the Fermi level ϵ{sub F} rather than to a change in the overlapping of wavefunctions, which play a minor role.