Structural and magnetic properties of La0.67(BaxCa1-x)0.33MnO3 perovskites (O≤x≤1)

The magnetic critical behavior in the series La-0.67(BaxCa1-x)(0.33)MnO3 (0 less than or equal to x less than or equal to 1) Of manganese perovskites is studied by means of de magnetic measurements. In this series the Mn4+/Mn3+ 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 less than or equal to 0.4 crystallize in the orthorhombic Pnma space group whereas samples with x greater than or equal to 0.5 in the rhombohedral R (3) over bar c space group. Arrott and scaling plots show that only in samples with x greater than or equal to 0.25 the magnetic properties follow the behavior expected for a conventional second-order ferromagnetic transition. The values of critical exponents (beta,gamma) are between those predicted for a three-dimensional Heisenberg model and those predicted by mean field theory. [S0163-1829(99)04501-4].