  Tunnel magnetoresistance (TMR) sensor is a highly sensitive magnetic field
sensor and is expected to be applied in various fields, such as magnetic
recording, industrial sensing, and bio-medical sensing. To improve the
detection capability of TMR sensors in low frequency regime it is necessary to
suppress the 1/f noise. We theoretically study 1/f noise of a tiny TMR sensor
using the macrospin model. Starting from the generalized Langevin equation, 1/f
noise power spectrum and the Hooge parameter are derived. The calculated Hooge
parameter of a tiny TMR sensor is much smaller than that of a conventional TMR
sensor with large junction area. The results provide a new perspective on
magnetic 1/f noise and will be useful for improvement of TMR sensors.
