Low-temperature heat-capacity studies ofR2Ni3Si5 (R=Pr, Nd, Sm, Gd, Tb, Dy, Ho)

Abstract

We report here our low temperature (2-30K) heat capacity, C p measurements of R 2 Ni 3 Si 5 (R=Pr, Nd, Sm, Gd-Ho). Large peaks in heat capacity data at magnetic transition temperatures (T N ) confirm the bulk nature of magnetic order in these compounds. In Nd 2 Ni 3 Si 5 , Gd 2 Ni 3 Si 5 , and Dy 2 Ni 3 Si 5 , magnetization studies indicated only one magnetic transition, whereas, heat-capacity data show two transitions. T N of the heavier rare-earth member, Tb 2 Ni 3 Si 5 , showing significant deviation from de Gennes scaling is notable. Magnetic entropy,ΔS, estimated from heat-capacity data suggest that the magnetic ground state is a doublet in R 2 Ni 3 Si 5 (R=Pr, Nd, Sm, Dy, Ho) and a quartet in Tb 2 Ni 3 Si 5 . In all the cases, ΔS, at T N is slightly less than that expected due to the suggested states, which we attribute to the occurrence of precursor effects of magnetic order above T N . Except for Gd 2 Ni 3 Si 5 , ΔS of the compounds does not reach the saturation limit of Rln(2J+1) even at 30 K, indicating the presence of crystalline electric field (CEF) effects. A hump in C p is observed below T N in Gd 2 Ni 3 Si 5 which is interpreted in terms of a possible amplitude-modulated magnetic spin structure.