Effect of oxygen off-stoichiometry on magnetic and magneto-transport properties of nanocrystalline under-doped LCMO

摘要

Magnetic and magneto-transport investigation of nanocrystalline under-doped manganite La_(0.875)Ca_(0.125)MnO_(3+δ) with δ = 0.0 (sample x1) and δ = 0.06 (sample x2) reveals that the dipolar interactions are primarily responsible for establishing ferromagnetic order in the insulating state and that the uniaxial magnetic anisotropy is stronger in x2. The reduction of magnetization and resistivity in x2 compared to that in x is brought about by the oxygen off-stoichiometry as it increases the concentration of Mn~(4+) ions. Bringing the crystallite size down to nanometer range induces an insulating-to-metal transition and a re-entrant insulating (ferromagnetic) phase at temperatures T < 30 K.