Correlation of structural distortion with magnetic properties in electron-doped Ca_(0.9)R_(0.1)MnO_3 perovskites (R= rare-earth)

摘要

A series of electron-doped orthorhombic-perovskite manganites Ca_(0.9)R_(0.1)MnO_3 (R=La, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, and Yb) are synthesized for a systematic study of their crystal structure and magnetic properties. The structural distortions, in terms of the average Mn-O-Mn bond angle θ_(Mn-O-Mn) and Mn-O bond length d_(Mn-O) characterized as a function of the A-site ionic size. Two degenerate vibration modes Q_1 and Q_3 are used for describing the bond length splitting and the evolution of the octahedral-site distortion. With R~(3+) doping, the magnetization increases markedly at low temperatures, which can be attributed to the formation of ferromagnetic clusters in the antiferromagnetic matrix. Both low temperature magnetization and paramagnetic susceptibility vary with the radius of R~(3+) ion and enhanced ferromagnetic domain is found in Ca_(0.9)Ho_(0.1)MnO_3. The Neel temperature T_N, varying from 100 to 116 K, is strongly dependent on the crystal structural distortions and can be well described as functions of three structural parameters θ_(Mn-O-Mn), d_(Mn-O), and A-site cation size variance σ~2. The best size matching between Dy~(3+) and Ca~(2+) leads to the highest T_N in Ca_(0.9)Dy_(0.1)MnO_3.