Magnetic and transport properties of Pb perovskites and Fe containing giant magnetoresistance perovskites

The magnetic and magnetoresistive properties of the Ln(0.7)Pb(0.3)Mn(1-x)Fe(x)O(3) (Ln = La, Nd, and x = 0, 0.1) perovskites, prepared by the solgel low temperature method, have been studied. In all cases the exact stoichiometry is different from the nominal one probably due to the presence of cation vacancies. All the phases exhibit ferromagnetic behavior with T-c values ranging form 345 K observed for La0.7Pb0.3MnO3 to 75 K for Nd0.7Pb0.3Mn0.9Fe0.1O3. The 10% Fe contribution lowers the T-c by about 130 K in the La compound and 90 K in the Nd one. These results can be interpreted in terms of antiferromagnetic coupling between Mn and Fe. However, the influence of the Nd ions is not well known although it seems not ordered down to 10 K. The magnetoresistence [MR = Delta R/R(0)] measured at 6 T in pellets of pressed powder reaches values of about 80% around the magnetic transition. (C) 1998 American Institute of Physics.