Enhancement of the magnetocaloric effect driven by changes in the crystal structure of Al-doped GGG, Gd sub(3)Ga sub(5-x)Al sub(x)O sub(12) (0 [< or =] x [< or =] 5)

The Gd sub(3)Ga sub(5-x)Al sub(x)O sub(12) (0 [< or =] x [< or =] 5) solid solution has been prepared using ceramic synthesis routes and the structural and magnetic properties were investigated using x-ray diffraction, magnetic susceptibility, chi , and isothermal magnetisation, M.(H), measurements. Our results indicate a contraction of the unit cell and more significant antiferromagnetic interactions as x increases. Despite the decrease in the magnetic polarisation on the application of a field and the corresponding decrease in the change in the magnetic entropy, Delta S, we find that Gd sub(3)Al sub(5)O sub(12) has a significantly higher observed (17%) and theoretical (14%) Delta S per unit mass than Gd sub(3)Ga sub(5)O sub(12). The theoretical increase in Delta S per unit volume (7%) is offset by the increased antiferromagnetic interactions in Gd sub(3)Al sub(5)O sub(12). The differences in Delta S are driven by a decrease in both the mass and the density as Al ions replace Ga ions. These results highlight the importance of changes to the crystal structure when considering materials for solid state magnetic cooling.