  We investigate the effect of partial replacement of extended 5d Ir4+ sites by
localized 3d Cr3+ moments on the magnetocaloric properties of Y2Ir2O7 (YIO)
pyrochlore iridates. We find that Y2Ir2-xCrxO7 (YICO) undergoes cluster glass
transition, possibly due to RKKY like interaction between localized Cr3+
moments occupying random sites in the pyrochlore network, mediated by 5d Ir
conduction electrons. The coexistence of ferromagnetic and antiferromagnetic
clusters give rise to the conventional and inverse magnetocaloric effect (MCE).
We observe significant enhancement of conventional as well as inverse MCE with
substitution. Although the value of conventional MCE and inverse MCE in
substituted Iridates are not large, the effect spans over a giant working
temperature window, thus leading to orders of magnitude enhancement of cooling
power, the value being comparable to standard magnetocalric materials.
