Thickness dependence of tunneling magneto-resistance effect in granular Fe-Al/sub 2/O/sub 3/ films

The magneto-transport properties of the granular Fe/sub 0.5/(Al/sub 2/O/sub 3/)/sub 0.5/ solids with various film thickness have been investigated. The temperature dependence of the resistivity shows that all samples follow a tunneling type equation /spl rho/(T)=/spl rho//sub 0/exp(T/sub 0//T)/sup 1//spl alpha// with /spl rho//spl ap/0.1/spl sim/1 /spl Omega/cm at 300 K and /spl alpha/=2. The results of magneto-resistance at 300 K indicate that the value is about 4.5% for thick films. It increases slowly with decreasing film thickness. At about 150 nm, a peak value of TMR is found, which is determined to be 5%. Then TMR drops sharply with further reducing film thickness. It becomes only 3% at t=20 nm. At low temperatures, the TMR effect becomes larger and shows similar thickness dependence. However, the values of T/sub 0/ that relate to the geometry of the tunneling barrier show behavior of opposite thickness dependence. A small T/sub 0/ is associated with a large TMR effect. In this report, the correlation of the film microstructure and the TMR effect are discussed in details.