  The binary compounds GdIr3, TbIr3 and HoIr3 are synthesized successfully and
found to form in macroscopic co-existence of two polymorphic phases: C15b and
AuCu3-type. The dc magnetization and heat capacity studies confirm that C15b
phase orders ferromagnetically, whereas the AuCu3 phase remains paramagnetic
down to 2 K. The frequency dependent ac-susceptibility data, time dependent
magnetic relaxation behavior and magnetic memory effect studies suggest that
TbIr3 and HoIr3 are cannonical spin-glass system, but no glassy feature could
be found in GdIr3. The critical behavior of all the three compounds has been
investigated from the magnetization and heat capacity measurements around the
transition temperature (TC). The critical exponents alpha, beta, gamma and
delta have been estimated using different techniques such as Arrott-Noaks plot,
Kouvel-Fisher plot, critical isotherm as well as analysis of specific heat data
and study of magnetocaloric effect. The critical analysis study identifies the
type of universal magnetic class in which the three compounds belong.
