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Is Electrical 1/f Noise in Tunneling Magnetoresistive Heads a Form of Equilibrium Noise?

Tunneling magnetoresistive (TMR) heads exhibit 1/f noise at the low end of their frequency range. A considerable fraction of this noise is still present when the junctions are magnetically saturated. This remnant electrical 1/f noise is much larger than the 1/f noise observed in small conductors of similar size and resistance, which has been shown to be caused by spontaneous fluctuations in the equilibrium resistance. This paper reports measurements on TMR heads to determine if the observed electrical 1/f noise is also present in the case of thermodynamic equilibrium, i.e., when the head is in thermal equilibrium and electrically unbiased. Reported are spectral noise measurements of the thermal (Johnson) noise which, according to the fluctuation-dissipation theorem, should become modulated in noise power by any resistance fluctuations. Since we found no 1/f noise in the observed unbiased TMR spectra, it was concluded that the electrical 1/f noise is due to resistance fluctuations caused by, and proportional to the electrical current through the junction. This noise is absent for zero current