Critical behavior of<mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"><mml:mrow><mml:msub><mml:mi mathvariant="normal">La</mml:mi><mml:mrow><mml:mn>1</mml:mn><mml:mo>−</mml:mo><mml:mi>x</mml:mi></mml:mrow></mml:msub><mml:msub><mml:mi mathvariant="normal">Sr</mml:mi><mml:mi>x</mml:mi></mml:msub><mml:mi mathvariant="normal">Mn</mml:mi><mml:msub><mml:mi mathvariant="normal">O</mml:mi><mml:mn>3</mml:mn></mml:msub></mml:mrow></mml:math><mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"><mml:mrow><mml:mo>(</mml:mo><mml:mn>0</mml:mn><mml:mo>⩽</mml:mo><mml:mi>x</mml:mi><mml:mo>⩽</mml:mo><mml:mn>0.35</mml:mn><mml:mo>)</mml:mo></mml:mrow></mml:math>by thermal diffusivity measurements

An ac photopyroelectric calorimeter has been used to measure the thermal diffusivity of the perovskite manganite family ${\mathrm{La}}_{1\ensuremath{-}x}{\mathrm{Sr}}_{x}\mathrm{Mn}{\mathrm{O}}_{3}$ on a set of single crystals with doping range $0\ensuremath{\leqslant}x\ensuremath{\leqslant}0.35$. Taking into account that the inverse of the thermal diffusivity has the same critical behavior as the specific heat, the critical exponent $\ensuremath{\alpha}$ 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 $(x&lt;0.10)$, where the transition is antiferromagnetic-paramagnetic, the critical exponent is consistent with the Heisenberg model $(\ensuremath{\alpha}=\ensuremath{-}0.11)$. For the highly doped samples $(x&gt;0.28)$, where there is a pure ferromagnetic-paramagnetic transition, the critical exponent is exactly that of an Ising behavior $(\ensuremath{\alpha}=+0.11)$. For $0.10\ensuremath{\leqslant}x&lt;0.28$ no universality class was found and this behavior has been discussed taking into account the complexity of the phase diagram in this concentration range.

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