Abstract
Fe40Al24O36 (atomic ratio) nano-structured granular films were prepared by rf reactive sputtering, and the microstructure, electrical and magnetic properties as well as the tunnelling magnetoresistance (TMR) effect were studied systematically. It is found that the samples consist of small Fe particles with the diameter around 2-4 nm separated by an Al2O3 dielectric matrix, and the conductance mechanism is thermally-activated tunnelling. The samples display superparamagnetic properties at room temperature. Considering the size distribution of metal particles, the magnetization and TMR curves can be fitted with the Langevin formula and the Inoue model quite well. TMR is caused by spin-dependent tunnelling, it is closely related to the structure and magnetic state of the samples. Under the optimal conditions, the TMR value reaches a maximum of 5.7% at room temperature under 1.6 T magnetic field.
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