Spin torque induced noise effect in TMR head

Recently hard disk drive (HDD) industry introduced a new hard disk drive (HDD) which adapted the perpendicular magnetic recording (PMR) media and tunneling magnetic resistance (TMR) head technology. TMR with MgO barriers has increased magnetoresistance (MR) ratio up to 230%. This increased sensitivity may amplify the noise effect. Also the sensing current which flows perpendicular in plane (CPP) direction can give the spin torque effect to the free layer and become an another noise source. This effect might be small in this current size TMR head, but could be an important noise source when the size of head is decrease with increasing the areal density.