Specific heat study of a holmium single crystal

The magnetic transition at the Neel temperature, T N , of the heavy rare-earth metal holmium has been examined by specific heat measurements. The transition at T N =(132.245+or-0.080)K is found to be continuous and the data around 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 )/T N . The value of the critical exponent alpha is 0.27+or-0.02 for the data in the critical regions -3.8<log 10 mod t mod <-1.2 below T N and -3.9<log 10 mod t mod <-2.9 above T N . The authors find that the scaling law alpha + = alpha - is valid and the condition T N + =T N - 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 log 10 mod t mod =-2.9 above but not below T N . An unidentified anomaly is observed in the specific heat of holmium at 98K.