Calorimetric Investigation of Magnetic Transitions in GdPdAl and TbPdAl.

A comparative specific heat (C P ) study of GdPdAl and TbPdAl compounds crystallizing in hexagonal ZrNiAl-type crystal-structure (space group P 6 ¯ 2 m) is presented. Consistent with earlier reports both the compounds show the signature of two magnetic transitions in magnetization data. The magnitude of the jump in C P at the high-temperature transition at T N 1 (∼ 47 K) in GdPdAl indicates ordering into an amplitude-modulated magnetic structure. The analysis of magnetic entropy change (S 4 f ) showed that about one-half of total S 4 f occurs below low temperature transition at T N 2 . This is in contrast to that seen in TbPdAl, where only one-third of the entropy of transition occurs below T N 2 . For both the compounds S 4 f tends to saturate to about 84% (for T > T N 1 ) of that expected for complete ordering of the rare earth moments, indicating incomplete removal of geometrical frustration. [ABSTRACT FROM AUTHOR]