Abstract
Metal/insulator composite materials have been fabricated by using co-sputtering at room temperature. Hall effect has been found to be greatly enhanced, when the metal volume fraction decreases from 1 to ∼0.5, in both magnetic and non-magnetic composite films. In non-magnetic Cu
x
–(SiO
2)
1−
x
composite films, nearly three orders of magnitude enhancement in the Hall coefficient is observed. This large enhancement of the Hall coefficient is not only significantly larger than the prediction of the classical percolation theory, but also occurs at a metal concentration identified to be the quantum percolation threshold, which has been accounted for in the framework of the local quantum interference effect. The greatly enhanced extraordinary Hall effect has been observed in different magnetic composites; however, it decreases with increasing temperature. Recently, we have fabricated soft magnetic composite films by using sputtering, which show a nearly temperature-independent giant Hall effect from 5 to 300
K.