Low - temperature heat - capacity studies of R 2 Ni 3 Si 5 „ R 5 Pr , Nd , Sm , Gd , Tb , Dy , Ho ...

We report here our low temperature (2230 K) heat capacity, Cp measurements of R2Ni3Si5 (R 5Pr, Nd, Sm, Gd-Ho). Large peaks in heat capacity data at magnetic transition temperatures (TN) confirm the bulk nature of magnetic order in these compounds. In Nd2Ni3Si5 , Gd2Ni3Si5 , and Dy2Ni3Si5 , magnetization studies indicated only one magnetic transition, whereas, heat-capacity data show two transitions. TN of the heavier rare-earth member, Tb2Ni3Si5 , showing significant deviation from de Gennes scaling is notable. Magnetic entropy, DS , estimated from heat-capacity data suggest that the magnetic ground state is a doublet in R2Ni3Si5 (R5Pr, Nd, Sm, Dy, Ho) and a quartet in Tb2Ni3Si5 . In all the cases, DS , at TN is slightly less than that expected due to the suggested states, which we attribute to the occurrence of precursor effects of magnetic order above TN . Except for Gd2Ni3Si5 , DS of the compounds does not reach the saturation limit of R ln(2J11) even at 30 K, indicating the presence of crystalline electric field ~CEF! effects. A hump in Cp is observed below TN in Gd2Ni3Si5 which is interpreted in terms of a possible amplitude-modulated magnetic spin structure. @S0163-1829~99!12605-5#