Structural and magnetic properties of La0.67−y(Sr,Ba,Ca)0.33+yMn1−xSnxO3 (x=0.01, 0.02, y=0, 0.07) perovskites

The magnetic critical behaviour of the manganese perovskite series La0.67−y(Sr,Ba,Ca)0.33+yMn1−xSnxO3 (x=0.01, 0.02, y=0, 0.07) is studied by means of dc magnetic measurements. The substitution of Mn by Sn ions in the samples results in a decrease of the transition temperature. The structure can be described by a rhombohedral unit cell (space group R-3C) for the samples where the A-site is occupied by La and Sr or La and Ba ions and an orthorhombic unit cell (space group Pnma) for the samples where the A-site is occupied by La and Ca ions. An increase of the cell volume is observed as Mn substituted by Sn ions in all samples. Arrott and scaling plots show that the samples, where the A-site is occupied by La and Sr or La and Ba ions, follow the behaviour of a conventional second-order ferromagnetic transition. The values of the critical exponents (β, γ) are between those predicted by the three-dimensional Heisenberg model and mean field theory. In contrast, the samples that contain La and Ca ions in the A-site show anomalous behaviour around the Curie point. Static disorder induced by Sn substitutions leads to a rounding of the transition.