Influence of 3d-4f interactions in the magnetic phases of RFexMn12−x (R=Gd, Tb, and Dy) compounds: Coexistence of ferromagnetism and antiferromagnetism at different crystallographic sites

Abstract

The structural and magnetic properties of tetragonal RFexMn12−x (R=Gd, Tb, Dy) compounds have been extensively studied by means of dc and ac susceptibilities, x-ray absorption spectroscopy at Gd-LIII edge, and neutron-powder-diffraction experiments. The substitution of Fe for Mn in RFexMn12−x not only influences the magnetic interactions on the 3d sublattice (the Néel temperature doubles, going from x=0 to x=6, and the compounds become ferromagnetic for x=8 with Curie temperatures of around 300 K), but also has a major effect on the magnetism of R. While in pure RMn12 the ordering temperatures of R, through R-R interactions, are close to liquid-helium temperatures, the substitution of Mn by Fe leads to the appearance of spin-glass-like behavior as well as to magnetic polarization effects between the 3d and 4f sublattices, together with the disappearance of the cooperative ordering of the R sublattice. This polarization is able to induce 4f magnetic moments below 150 K. In addition, the 3d magnetic interactions are modified by the presence of magnetic R ions in the system: both ferromagnetic and antiferromagnetic orderings are observed simultaneously over different crystallographic sites. A general analysis of the available experimental data allows us to establish the magnetic phase diagram of RFexMn12−x.