Critical behaviour of transport coefficients at a structural ferromagnetic transition

The electrical resistivity rho and its temperature derivative dsub(rho)/dT of two TbZn monocrystals have been studied over a large temperature range encompassing the Curie temperature (Tsub(c) approximately 199.56 K) and the spin reorientation temperature (Tsub(r) approximately 61.9 K). Different experimental conditions have been used to sort our the interesting features. Particular emphasis is put on the critical behaviour analysis. A detailed study shows that a scaling law behaviour characterised by a finite but fairly small critical exponent cannot be experimentally distinguished from a logarithmic dependence above Tsub(c). The cross-over temperature to the mean field behaviour is also pointed out. Outside the critical region, the anomalously large dsub(rho)/dT values observed over most of the ferromagnetic range are explained using a mean field model. Finally, the critical behaviour of dsub(rho)/dT near Tsub(r) is analysed, and the resemblance to the anomaly observed in the specific heat is pointed out. (author)