Spin-Torque Effect on Thermally Excited Magnetization Fluctuation Noise in Tunneling Magnetoresistive Read Heads

The spin-torque (ST) effect on the thermally excited magnetization fluctuation noise (thermal mag-noise) in tunneling magnetoresistive (TMR) read heads is investigated in the GHz range using noise spectra. The strong noise spectral peak around 3.1 GHz is attributed to thermal mag-noise originating from the free layer. The peak intensity and linewidth strongly depend on both the external magnetic field and current density. These features demonstrate that the ST effect significantly influences the thermal mag-noise as the current density increases up to the critical current density. Additionally, it is speculated that the non-thermal fluctuation noise originating from ST in the TMR heads as well as in current perpendicular to plane giant magnetoresistive (CPP-GMR) heads is generated above a critical current of approximately 2.5×10¹¹ A/m².