Magnetic inhomogeneity and colossal magnetoresistance in manganese oxides

The magnetic and magnetotransport properties of the manganites, R(1-x)A(x)MnO(z) (R = La, Pr, Nd; A = Ca, Sr, Ba), are strongly dependent on the doping level x and oxygen stoichiometry z. For x greater than or equal to similar to 0.2, stoichiometric R(1-x)A(x)MnO(3) was found to have a small temperature independent coercivity of 5-30 Oe and the saturation magnetiztion (similar to 90 emu/g) of fully aligned Mn ions. Oxygen deficient (or x < 0.2) R(1-x)A(x)MnO(z) has a saturation magnetization smaller than that of fully aligned Mn spins and shows an enhancement and temperature dependence of the coercivity, and spin freezing behavior, The latter is characterized by a peal; in zero field cooled (ZFC) magnetization. Our data suggest that oxygen deficient or low doped manganites are magnetically inhomogeneous. We discuss possible origins of the magnetic inhomogeneity and its influence on the colossal magnetoresistance.