  A detailed study on the crystal structure and bulk magnetic properties of Cr
substituted Ising type lanthanide gallium garnets
$Ln_3\text{CrGa}_4\text{O}_{12}$ ($Ln$ = Tb, Dy, Ho) has been carried out using
room temperature powder X-Ray and neutron diffraction, magnetic susceptibility,
isothermal magnetisation and heat capacity measurements. The magnetocaloric
effect (MCE) in $Ln_3\text{CrGa}_4\text{O}_{12}$ is compared to that of
$Ln_3\text{Ga}_5\text{O}_{12}$. In lower magnetic fields attainable by a
permanent magnet ($\leq$ 2 T), Cr substitution greatly enhances the MCE by 20%
for $Ln$ = Dy and 120% for $Ln$ = Ho compared to the unsubstituted
$Ln_3\text{Ga}_5\text{O}_{12}$. This is likely due to changes in the magnetic
ground state as Cr substitution also significantly reduces the frustration in
the magnetic lattice for the Ising type $Ln_3\text{Ga}_5\text{O}_{12}$.

Materials Science