  By virtue of the itinerant electron metamagnetism (IEM), the RCo2 compounds
with R=Er, Ho and Dy are found to show first order magnetic transition at their
ordering temperatures. The inherent instability of Co sublattice magnetism is
responsible for the occurrence of IEM, which leads to interesting magnetic and
related properties. The systematic studies of the variations in the magnetic
and magnetocaloric properties of the RCo2-based compounds show that the
magnetovolume effect plays a decisive role in determining the nature of
magnetic transitions and hence the magnetocaloric effect (MCE) in these
compound. It is found that the spin fluctuations arising due to the
magnetovolume effect reduce the strength of IEM in these compounds, which
subsequently lead to a reduction in the MCE. Most of the substitutions at the
Co site are found to result in a positive magnetovolume effect, leading to an
initial increase in the ordering temperature. Application of pressure, on the
other hand, causes a reduction in the ordering temperature due to the negative
magnetovolume effect. A comparative study of the magnetic and magnetocaloric
properties of RCo2 compounds under various substitutions and applied pressure
is presented. Analysis of the magnetization data using the Landau theory has
shown that there is a strong correlation between the Landau coefficient (B) and
the MCE. The variations seen in the order of magnetic transition and the MCE
values seem to support the recent model proposed by Khmelevskyi and Mohn for
the occurrence of IEM in RCo2 compounds.
