Magnetoimpedance in La0.67Pb0.33MnO3 manganite prepared by sol-gel method

In the present work, manganite La(0.67)Pb(0.33)MnO(3) was prepared by the sol-gel method. The difference between metal-insulator transition temperature T(MI) (217 K) and Curie temperature T(c) (342 K) in the sol-gel nanocrystalline manganite is mainly due to the grain boundary effect. The breaking of Mn-O-Mn bonds and strong scattering at the grain boundary cumber the transport. At room temperature 300 K, impedance and resistance increase with increasing frequency of ac currents. The observed dc magnetoresistance in sol-gel La(0.67)Pb(0.33)MnO(3) is related to the spin-polarized inter-grain tunneling and spin-dependent scattering at grain boundaries. The sol-gel manganite shows the magnetoimpedance characteristics, which are different from those of traditional sintered manganites and metallic giant magnetoimpedance materials. For sol-gel La(0.67)Pb(0.33)MnO(3) at low frequencies, the impedance experiences a peak under a low longitudinal field. In contrast, at high frequencies the peak phenomenon disappears, and the impedance drops sharply with low fields, which is due to the intergrain or grain boundary effect. The permeability also sensitively varies with an application of transverse field. The magnetoimpedance effect in sol-gel nanocrystalline manganite is influenced by both field-induced permeability change and dc magnetoresistance. (C) 2008 Elsevier B.V. All rights reserved.