Electrical Transport and Magnetoresistance in the Sol-Gel Prepared La_2/3Ca_1/3Mn_1-xTE_xO₃ (x = 0 and 4%, TE=Cu and Zn) Polycrystalline Samples

A comparative study of electrical transport and magnetoresistance (MR) is performed for sol-gel prepared samples of nominal composition La_2/3Ca_1/3MnO₃, La_2/3Ca_1/3Mn_1-xCu_xO₃ and La_2/3Ca_1/3Mn_1-xZn_xO₃ with x = 4%. Compared with La_2/3Ca_1/3MnO₃, the introduction of Cu or Zn causes a significant downward shift of insulator--metal transition and a sharp MR peak near the transition. The sharp MR peak becomes observable even upon the application of low magnetic fields. It is also shown that although the same behaviour of transport and MR is observed, the sample containing Cu stands out clearly from the sample containing Zn for a substantial enhancement in MR near the transition.