Effect of rare earth ion in the thermopower of [formula omitted] compounds with [formula omitted] and R=Gd and Tb

Abstract

The magnetocaloric ferromagnetic compounds with R 5 ( Si x Ge 1 - x ) 4 composition are very sensitive to the Si:Ge ratio ( x ) and the particular Rare earth (R) ion. Here we study the thermopower S ( T ) behavior of samples with a similar x ∼ 0.5 ratio but different rare earth ions: Gd 5 ( Si 0.45 Ge 0.55 ) 4 and Tb 5 ( Si 0.5 Ge 0.5 ) 4 , between 10 and 290 K. Above the Curie temperature ( T C ) both S and its T -dependence do not change with the R-ion but, upon cooling, a first-order magneto-structural transition occurs at T S (close to T C ) causing an abruptness in thermopower ( Δ S / S ∼ 32 % ) . At low temperatures very distinct S ( T ) behavior is observed, and a spin reorientation transition occurs in the Tb compound.