Magnetic properties of (rare earth)Al2intermetallic compounds

Abstract In this paper the most important magnetic properties of non-S-state ferromagnetic single crystalline REAl2 (RE ≡ rare earch) intermetallic compounds with well localized 4f electrons are reviewed. Particular emphasis is placed on the static magnetization and on the magnetic excitations. The review demonstrates that for a single REAl2 compound a cubic crystalline field (CF) provides an excellent basis for a quantitative description of the magnetization, including the magnetocrystalline anisotropy by using molecular-field theory. This approach is also appropriate in many cases for the magnetic part of the molar specific heat in a temperature range where contributions from spin waves can be neglected. Taking into account the magnetic interactions of different ions within the random-phase approximation, it is also possible in most cases to describe the low-temperature behaviour of the magnetic excitations. In general a consistent description of various other important magnetic properties can also be given. However, it is obvious from the results discussed here that in order to remove the remaining discrepancies between experiment and theory, it is not enough to include, for example, magnetostriction, anisotropic exchange and higher multiplets by retaining at the same time the basic theory. Instead, it is believed that new, and so far undetermined, concepts are needed. By comparing different REAl2 compounds, it is possible to define reduced crystal-field parameters that all have the same sign and order of magnitude. To a lesser degree, such systematic behaviour is also observed for the exchange parameters. But this comparison also clearly shows that more sophisticated treatments than those mentioned above are necessary to obtain a substantial improvement of the systematic description within the isostructural series of REAl2 compounds.