Spin Torque Enhancement of Thermally Excited Ferromagnetic Resonance in Tunneling MR Heads

In this paper, we present an experimental study on the effect of spin torque to the thermally excited ferromagnetic resonance, known as mag-noise, in tunneling magnetoresistive (TMR) read heads that are currently used in hard disk drive applications. Power spectra densities of the tunnel junction read heads under a dc bias current over a frequency range from 0.5 to 12 GHz are obtained as functions of applied magnetic field and bias current. All the important characteristics of spin torque driven microwave oscillations can be clearly identified in the observed power spectral densities. In contrast to current-perpendicular-to-plane spin valve sensors, no 1/f-like noise below 2 GHz has been observed