Geometrical Dependence of Thermally Excited Mag-Noise Spatial Distribution in Magnetic Tunnel Junction Sensors

The relation between the spatial distribution of thermally excited mag-noise and the geometry of magnetic tunnel junction (MTJ) sensors was studied by micromagnetic simulation. The thermally excited mag-noise in MTJ sensors with rectangular cross section is found to exhibit a spatial distribution in which the tendency could be described as edge effect. The level of this edge effect changes with the aspect ratio of the free layer. As the aspect ratio increases from 0.6 to 1.4, the edge effect is suppressed linearly by nearly two times. This is ascribed to the change of the stiffness field in the free layer. On the other hand, the edge effect is not applicable for MTJ sensors with circular cross section. The central regions of the circular MTJ sensors are the main contributor of the mag-noise. These findings further our understanding on mag-noise behavior in MTJ sensors, and they are useful for suppressing noise in sensor design.