Large magnetoresistance in (La1-xCaxMnO3)1-y:ZrO2 composite

Colossal magnetoresistance (CMR) composite materials have been synthesized to explore the possibility of improving magneto-transport and structural properties in CMR systems. In this work we describe (La1-xCaxMnO3)(1-y) (LCMO) (ZrO2)(y) (xapproximate to0.3 and 0.0less than or equal toyless than or equal to0.40 mole %) composites that have been synthesized using a modified (non Pechini type) sol-gel technique. Magnetoresistivity of the composites was evaluated at 5 T field and in the temperature range 5-300 K. The composites show higher magnitude of MR compared to pure LCMO. The MR rises from a base value 76%, for the case y=0, to a maximum value of 93.8%, obtained at y=0.05. dc susceptibility measurements show a distinct ferromagnetic to paramagnetic transition in all composites. The ferromagnetic transition temperature (T-C) drops from 225 K in pure LCMO (y=0) to 121 K in y=0.05 and then slowly rises to 157 K as y increases. The plots of zero field cooled susceptibility chi(ZFC) (T) and field cooled susceptibility chi(FC) (T) diverge clearly below T-C, indicating magnetic irreversibility. The composite exhibits a clear metal-insulator transition (T-MI) at or just above the magnetic transition. The peak resistivity rho(MI) at the metal-insulator transition also exhibits interesting changes. For pure LCMO polycrystals, rho(MI)=102 Omega cm, but it increases to 228 Omega cm for y=0.05 and then gradually decreases to 1.94 Omega cm for ygreater than or equal to0.10. The phase evolution in the LCMO:ZrO2 composites was studied by x-ray powder diffraction and correlated to the magnetic and electrical properties. (C) 2003 American Institute of Physics.