Specific heat study of a holmium single crystal

Abstract

The magnetic transition at the Neel temperature, TN, of the heavy rare-earth metal holmium has been examined by specific heat measurements. The transition at TN=(132.245+or-0.080)K is found to be continuous and the data around 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)/TN. The value of the critical exponent alpha is 0.27+or-0.02 for the data in the critical regions -3.8<log10 mod t mod <-1.2 below TN and -3.9<log10 mod t mod <-2.9 above TN. The authors find that the scaling law alpha += alpha - is valid and the condition TN+=TN- is obeyed in the critical regions. The value of alpha (=0.27) that they obtain is not close to the predictions of renormalisation group theory for magnetic systems with short-range exchange interactions. A cross-over from the critical region to a region with different behaviour is observed at log10 mod t mod =-2.9 above but not below TN. An unidentified anomaly is observed in the specific heat of holmium at 98K.