Effects of Ca-doping on the transport and magnetic properties of La1.4Sr1.6Mn2O7

Detailed structural analysis, DC electric resistivity, and AC magnetic susceptibility measurements have been performed to study the lattice, transport, and magnetic properties of polycrystalline La-1.4(Sr1 - xCax)(1.6) Mn2O7, with x = 0, 0.1, 0.2, and 0.3. We concentrate on the effects that resulted from the partial replacement of Sr2+ ions by smaller Ca2+ ions. All four compounds are single phase, with a structure that may be well-described using a tetragonal symmetry of space group 14/mmm. Ca doping causes the insulator-to-metal and paramagnetic-to-ferromagnetic transitions to occur at lower temperatures and the system re-enters the insulating state at lower temperatures. Several peaks are clearly seen in the temperature dependence of the AC susceptibility. Based on their behavior under an applied DC field, these peaks may be grouped into three types of different origin associated with charge ordering, Mn spin ordering and magnetic fluctuations. (C) 2000 Elsevier Science B.V. All rights reserved.