Structural and magnetic properties of ${\mathrm{La}}_{0.67}({\mathrm{Ba}}_x{\mathrm{Ca}}_{1-x}{)}_{0.33}{\mathrm{MnO}}_3$ perovskites $(0\mathrm{}<~x<~1)$

The magnetic critical behavior in the series ${\mathrm{La}}_{0.67}({\mathrm{Ba}}_x{\mathrm{Ca}}_{1-x}{)}_{0.33}{\mathrm{MnO}}_3$ $(0\mathrm{}<~x<~1)$ of manganese perovskites is studied by means of dc magnetic measurements. In this series the ${\mathrm{Mn}}^{4+}{/\mathrm{M}\mathrm{n}}^{3+}$ ratio is kept constant while Ca ions are substituted by the larger Ba ions resulting in structural changes accompanied by an increase of the transition temperature from 265 to 340 K. Samples with $x<~0.4$ crystallize in the orthorhombic $\mathrm{Pnma}$ space group whereas samples with $x>~0.5$ in the rhombohedral $R3\mathrm{}¯c$ space group. Arrott and scaling plots show that only in samples with $x>~0.25$ the magnetic properties follow the behavior expected for a conventional second-order ferromagnetic transition. The values of critical exponents (β,γ) are between those predicted for a three-dimensional Heisenberg model and those predicted by mean field theory.