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Enhancement of the magnetocaloric effect driven by changes in the crystal structure of Al doped GGG, Gd3Ga5-xAlxO12 (0 < x < 5)

The Gd3Ga5-xAlxO12 (0 < x < 5) solid solution has been prepared using ceramic synthesis routes and the structural and magnetic properties 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 application of a field and the corresponding decrease in the change in the magnetic entropy we find that Gd3Al5O12 has a significantly higher observed (17%) and theoretical (14%) DS per unit mass than Gd3Ga5O12. Per unit volume the theoretical increase in DS (7%) is offset by the increased antiferromagnetic interactions in Gd3Al5O12. The differences in DS are driven by a decrease in both the mass and 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.