Critical behaviour of RMnO3 (R = La, Pr, Nd) by thermal diffusivity and specific heat measurements

An ac photopyroelectric calorimeter has been used to measure the thermal diffusivity and specific heat of the perovskite manganites RMnO3 (R ≤ La, Pr, Nd) close to their magnetic transitions. Taking into account that the inverse of the thermal diffusivity has the same critical behaviour as the specific heat, the critical exponent α of the magnetic transition has been obtained by means of both magnitudes. The results in all cases are consistent with the Heisenberg model (α ≤ -0.11), irrespective of the rare-earth ion. © 2005 IOP Publishing Ltd