The critical specific heat of terbium

Abstract

Specific heat measurements have been carried out on a high-purity single crystal of terbium of mass 3.734 g between temperatures of 200 and 400K. The data around the Neel temperature T_N, have been analysed in terms of the equation C^+or-=(A^+or-/ alpha ^+or-) mod t mod^{- alpha +or-}(1+E^+or- mod t mod ^x+or-)+B^+or-+D^+or-t where t=(T-T_N^+or-)/T_N^+or-. The parameters obtained from our best fit are alpha ⁺= alpha =-0.20+or-0.03, A⁺/A^-=0.58+or-0.34, B⁺=B^-=21.68+or-13.93 J mol^-1 K^-1, E⁺/E^-=-2.06+or-4.12, D⁺=D^-=4.99 J mol^-1 K^-1 and T_N⁺=T_N^-=229.9503+or-0.0035K. This fit is valid in the critical regions -3.4<lg mod t mod <-1.5 below T_N and -3.9<lg mod t mod <-2.2 above T_N. The authors find that the relation T_N⁺=T_N^- is obeyed and that the scaling law alpha ⁺= alpha ^- is valid in this region. In order for the condition B⁺=B^-, predicted by theory, to be satisfied they have found it necessary to include the confluent singular term in E in the fit. The value of alpha (=+0.20) that the authors obtain is not close to the predictions of renormalisation group theory for magnetically collinear systems with short-range interactions. A cross-over from the critical region to a region with different behaviour is observed at lg mod t mod =-2.2 above T_N, but not below it.