Physical properties of the doped manganites Ln(0.5)M(0.5)MnO(3) (Ln = Pr, La; M = Sr, Ca, Ba)

We present the structural, magnetic and electrical properties of some manga nese oxides such as Ln(0.5)M(0.5)MnO(3) (Ln = La, Pr and M = Ca, Sr, Ba) in which the average ionic radius (r(A)) of the A site cation is varied while keeping the Mn3+/Mn4+ ratio fixed to 1. All the studied samples have a per ovskite structure with rhombohedral or orthorhombic distortion. This distor tion was related to the A cation size. The lattice volume increases lineral y with [r(A)] in all the range 1.179-1.3264 Angstrom. The magnetic investig ation shows that the magnetic transition temperature T-t and magnetisation saturation M-s have similar behaviour by increasing and decreasing with [r( A)] The electrical measurements show conduction by small polarons attribute d to a large canting angle theta in all the range 4-300 K in the two ferrom agnetic compounds La0.5Sr0.5MnO3 and La0.5Ca0.5MnO3.