Frustration in rare earth intermetallic compounds

The intermetallic compounds of rare earths with non-magnetic metals exhibit a large variety of magnetic behaviours arising from the competition of Iona-range exchange interactions between 4f ions in the presence of magnetocrystalline anisotropy. This competition results in frustrated magnetic states such as collinear incommensurate, helimagnetic, fan, long-period commensurate or antiphase structures. The anisotropy plays a crucial role in the existence and temperature dependence of these structures, according to the uniaxial (Ising-like) or planar (XY) character of the compounds, as well as to the Kramers or non-Kramers type of the rare earth. In some peculiar situations, mixed magnetic structures may even occur at low temperature, where two kinds of equivalent magnetic sites coexist, with a high- and a low-moment state, respectively. The addition of antiferroquadrupolar coupling may also favour multiaxial, multi-Q antiferromagnetic structures, in particular in cubic systems. In all these cases, applying a magnetic field results in magnetization processes showing a metamagnetic behaviour, with the presence of one or several well-defined plateaus separated by more or less sharp transitions. A thorough microscopic analysis of all these phenomena can be carried out by using an appropriate model, such as the self-consistent periodic field model. A few examples will illustrate the various effects of frustration in these intermetallic magnetic systems. (C) 2001 Elsevier Science BY All rights reserved.