Spin transfer induced noise in CPP read heads

In this paper, spin transfer induced magnetic noise in current-perpendicular-to-plane (CPP) spin valve heads is investigated via micromagnetic modeling with spin transfer torque included. It is found that there exists of a critical sense current density beyond which the spin transfer effect yields a substantial noise with a pronounced (1/f(n)) spectral content at low frequencies. This magnetic noise arises from the essentially chaotic magnetization precessions excited by the spin transfer effect that can effectively acts as energy pumping to the spin system. The onset of the noise occurs when the pumping rate becomes equal to the rate of energy dissipation. The critical current density is found to be proportional to the damping constant alpha as well as the longitudinal bias field.