Effects of magnetization on hole localization and MnO(sub 6) octahedra disorder in hole-doped lanthanum manganese perovskites

摘要

The authors review the distortions of the MnO(sub 6) octahedra reduced by magnetization in hole-doped lanthanum manganese perovskites. The systems they consider include the colossal magnetoresistance (CMR) samples La(sub 1(minus)x) Ca(sub x)MnO(sub 3) (x = 0.21, 0.25, 0.30), La(sub 0.76)Ba(sub 0.33)MnO(sub 3), and a poorer quality La(sub 0.76)Pb(sub 0.33)MnO(sub 3) sample. They also report preliminary work on three samples of oxygen-doped LaMnO(sub 3+(delta)) and a lanthanum-deficient La(sub 0.9)MnO(sub 3) sample. They find the same exponential relationship between the removal of the distortion and the sample magnetization in the Ba- and Pb-doped CMR samples as was found previously for the Ca doped samples. The MnO(sub 6) distortion in the oxygen-doped materials is found to slightly reduce below the magnetic transition, although much less so than in the CMR samples. Above T(sub C), the antiferromagnetic LaMnO(sub 3.006) sample shows a softer temperature dependence of the Mn-O bond length distribution broadening. Surprisingly, even this sample shows deviations from thermal (Debye) behavior near T(sub N), possibly due to FM coupling within MnO planes.