Magnetic entropy change in the Ge-rich alloys Gd-Si-Ge

We have studied the temperature and field dependence of the magnetocaloric effect in the Ge-rich alloys Gd/sub 5/(Si/sub x/Ge/sub 1-x/)/sub 4/, where x=0.0825, 0.15, and 0.1875. The low field susceptibility shows a two-step magnetic ordering at the Curie temperature T/sub C/ and the Neel temperature T/sub N/. The T/sub C/ of the different compositions covers the temperature range 67 K-108 K while T/sub N/ remains constant at around 133 K. The magnetic entropy change (delta)S/sub M/(T) as a function of applied field up to 7 Tesla is characterized by a second-order magnetic phase transition around T/sub N/ and a first-order transition around T/sub C/. The maximum magnetic entropy change around T/sub N/ is only about 3 J.kg/sup -1/.K/sup -1/, but it is much larger around T/sub C/. It rapidly reaches a saturation plateau of about 40-50 J.kg/sup -1/.K/sup -1/, which widens with increasing field. The width of the plateau at an applied field of 7 T is about 20 K. These results indicate that the Ge-rich alloys are potentially good candidates for MR applications at low temperature.