Reader Noise Due to Thermally Driven Asymmetric Oscillations

摘要

A new mechanism of low-frequency (LF) (<;2 GHz) thermal noise generation in magnetoresistive readers is described and confirmed experimentally. A mechanical model of a bi-harmonic oscillator is simulated at finite temperature by a numerical analysis of the Langevin equation in order to illustrate the concept. Filtered LF waveforms strongly correlate with resonance amplitude fluctuations and expose 1/f -like spectra. We apply this learning to reader output waveforms, proving the presence of the phenomenon for both free layer and synthetic antiferromagnet resonance lines. The impact of spin-momentum transfer is also seen by virtue of different correlation coefficients at positive and negative bias current values.