NOISE PROPERTIES OF FERROMAGNETIC TUNNEL-JUNCTIONS

We report measurements of voltage fluctuations in magnetic tunnel junc tions which exhibit both high and low magnetoresistance (MR). The volt age noise power normalized to the square of the junction bias voltage was 10(-14)/Hz at a frequency of 1 Hz in a high MR junction. Low MR ju nctions had significantly higher noise power at 1 Hz and the origin of the noise was not magnetic. In these junctions, random telegraph nois e was observed over a wide range of temperatures and junction biases. The results are consistent with a two-channel model of conduction, one of which is spin independent and gives rise to large noise. A noise m easuring technique provides evidence for bias-dependent current-path r earrangements. The data support the existence of an inhomogeneous (fil amentary-like) current-flow pattern across the tunnel junction associa ted with the spin-independent channel. (C) 1998 American Institute of Physics. [S0021-8979(98)09023-9].