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Abstract:

An ac photopyroelectric calorimeter has been used to measure the thermal diffusivity of the perovskite manganite family La1-xSr xMnO3 on a set of single crystals with doping range 0≤x≤0.35. Taking into account that the inverse of the thermal diffusivity has the same critical behavior as the specific heat, the critical exponent a of the magnetic transitions has been obtained. The results point to short-range interaction models for pure magnetic transitions. In the pure and lightly doped samples (x<0.10), where the transition is antiferromagnetic-paramagnetic, the critical exponent is consistent with the Heisenberg model (α=-0.11). For the highly doped samples (x>0.28), where there is a pure ferromagnetic- paramagnetic transition, the critical exponent is exactly that of an Ising behavior (α=+0.11). For 0.10≤x<0.28 no universality class was found and this behavior has been discussed taking into account the complexity of the phase diagram in this concentration range.