Low-temperature heat-capacity studies of R₂Ni₃Si₅ (R=Pr, Nd, Sm, Gd, Tb, Dy, Ho)

Abstract

We report here our low temperature (2-30K) heat capacity, C_p measurements of R₂Ni₃Si₅ (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 Nd₂Ni₃Si₅, Gd₂Ni₃Si₅, and Dy₂Ni₃Si₅, magnetization studies indicated only one magnetic transition, whereas, heat-capacity data show two transitions. T_N of the heavier rare-earth member, Tb₂Ni₃Si₅, 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 R₂Ni₃Si₅ (R=Pr, Nd, Sm, Dy, Ho) and a quartet in Tb₂Ni₃Si₅. 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 Gd₂Ni₃Si₅, 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 Gd₂Ni₃Si₅ which is interpreted in terms of a possible amplitude-modulated magnetic spin structure.