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 l ow temperature method, have been studied. In all cases the exact stoichiome try is different from the nominal one probably due to the presence of catio n vacancies. All the phases exhibit ferromagnetic behavior with T-c values ranging form 345 K observed for La0.7Pb0.3MnO3 to 75 K for Nd0.7Pb0.3Mn0.9F e0.1O3. The 10% Fe contribution lowers the T-c by about 130 K in the La com pound 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) 199 8 American Institute of Physics.