Electronic Noise in Magnetic Tunnel Junctions

We have studied bias and magnetic field dependence of voltage noise in metallic magnetic tunnel junctions with areal dimensions of order 1µm. We generally observe noise with Gaussian amplitude distribution and pure 1/f power spectra at low frequencies. The 1/f noise scales with bias voltage as V². Two kinds of deviations from this low frequency behavior have been observed. One is a fixed magnetic field when the junction bias reaches above a critical value, the other occurs at a fixed bias when the external magnetic field brings the sample to certain magnetic configurations. In both cases the noise spectra become dominated by Lorentzian noise and in both cases we have observed two level fluctuators in the time domain. The bias dependent noise we attribute to charge traps in the tunnel barrier. The field dependent noise is associated with the switching of the magnetization direction of portions of the top electrode, which we believe to be reversible.