Effects of cation size disorder and lattice distortion on metamagnetism in phase-separated manganites

The effects of A-site cation size disorder in ABO3 type charge-ordered and antiferromagnetic Pr0.5Ca0.5MnO3 system have been studied by substituting La3+, Sr2+ or Ba2+, while keeping the valency of Mn ions and the tolerance factor (t=0.921) constant in the substituted compounds. We find that the substitutions by these larger cations induce successive sharp step-like metamagnetic transitions at 2.5 K. The critical field for metamagnetism is the lowest for 3% Ba substituted compound, which has the largest A-site cation size disorder and the least distorted MnO6 octahedra, among the compounds reported here. These cation substitutions give rise to ferromagnetic clusters within antiferromagnetic matrix, indicating phase-separation at low temperatures. The growth of the clusters is found to vary with the substitution amount. The local lattice distortion of MnO6 octahedra enhances the charge ordering temperature and reduces the magnetization at high fields (>1 T) in these manganites.