Critical behaviour of transport coefficients at a structural-ferromagnetic transition. I. Electrical resistivity of TbZn

The electrical resistivity rho and its temperature derivative d rho /dT of two TbZn monocrystals have been studied over a large temperature range encompassing the Curie temperature (T_c approximately 199.56K) and the spin reorientation temperature (T_r approximately 61.9K). 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 T_c. The cross-over temperature to the mean field behaviour is also pointed out. Outside the critical region, the anomalously large d rho /dT values observed over most of the ferromagnetic range are explained using a mean field model. Finally, the critical behaviour of d rho /dT near T_r is analysed, and the resemblance to the anomaly observed in the specific heat is pointed out.