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 TN, 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-TN+or-)/TN+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 TN+=TN-=229.9503+or-0.0035K. This fit is valid in the critical regions -3.4<lg mod t mod <-1.5 below TN and -3.9<lg mod t mod <-2.2 above TN. The authors find that the relation TN+=TN- 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 TN, but not below it.