Tunneling magnetoresistance and magnetic properties of Fe-Al2O3 nanogranular films

Tunneling giant magnetoresistance (MR) of the Fe-Al2O3 nanogranular films has been observed over a wide range of Fe volume fraction x and it took a maximum of 4.4% at room temperature for the film with x = 0.45 at H = 10 kOe. Furthermore, the field dependence of MR of the samples is well described by the form proportional to the square of the magnetization. Moreover, an estimate of the magnetic anisotropy energy density K-u increases with the decrease of x, yielding a value 2 orders of magnitude greater than the value for bulk Fe when x = 0.23. The Bloch's law, M-S(T) = M-S0(1-BTb), can also hold for all the samples but with nonbulk parameters dependent on the Fe volume fraction. These results reveal a percolation effect on the magnetic properties, as well as the conductance, in such nanogranular films. (C) 2001 American Institute of Physics.