Electric and magnetic behaviour in double doped La_2/3+4x/3Sr_1/3−4x/3Mn_1−xMg_xO₃

Abstract

The double-doped La2/3+4x/3Sr1/3−4x/3Mn1−xMgxO3 samples with fixed Mn3+/Mn4+ ratio equal to 2/1 are investigated by means of magnetism and transport measurements. Phase separation is observed at temperature higher than Tconset for x = 0.10 and 0.15. For x = 0.10, rather strong phase separation induces drastic magnetic random potential and results in the localization of carriers. Thus, the variable-range hopping process dominates. For other samples, there is no or only weak phase separation above Tconset. Thus, thermal activation mechanism is responsible for the high temperature transport behaviour. For x = 0.20 and 0.25, unexpected AFM behaviour is observed at low temperature. All these results are well understood by considering the special role of the ``double-doping".