Mossbauer studies of Fe-Pb-O granular films with enhanced tunneling magnetoresistance effect

From our previous studies, it has been found that the Fe-Pb-O granular films which have been adequately annealed exhibit an enhanced tunneling magnetoresistance effect (TMR). The TMR effect is about 10% at room temperature, which can be claimed as the maximum value ever detected so far. In this report the TMR effect of Fe-Pb-O granular films from different annealing time have been investigated. The Mossbauer spectrometer was used to collect the information of Fe magnetic microstructure. It has been found that the tunneling barrier from the magnetic compound formed between a-[Fe.sup.2][O.sub.3] and PbO plays an important role in obtaining large TMR effect. And the non-magnetic Fe-Pb-O compounds which exist on the surface of iron granules as a thin layer and grow with annealing time seem to decrease TMR effect.