Giant Magnetocaloric Effect inGd5(Si2Ge2)

An extremely large magnetic entropy change has been discovered in $\mathrm{Gd}{}_5\left(\mathrm{Si}{}_2\mathrm{Ge}{}_2\right)$ when subjected to a change in the magnetic field. It exceeds the reversible (with respect to an alternating magnetic field) magnetocaloric effect in any known magnetic material by at least a factor of 2, and it is due to a first order $\left[\mathrm{ferromagnetic}\right(\mathrm{I})\leftrightarrow \mathrm{ferromagnetic}(\mathrm{II}\left)\right]$ phase transition at 276 K and its unique magnetic field dependence.