Magnetic noise spectra and spin transfer torque of a magnetic tunnel junction with an exchange biased synthetic ferrimagnetic reference layer

We investigate magnetic thermal noise spectra in magnetic tunneling junction with spin transfer torque. The basic structure of the examined magnetic tunneling junction is PtMn/F-3/Ru/F-2/MgO/F-1, where F-1,F-2,F-3 are ferromagnetic layers. F-1 acts as a soft free layer, while PtMn/F-3/Ru/F-2, an exchange biased synthetic ferrimagnet structure, serves as a fixed reference layer. With the assumption of rigid fixed reference layer, the magnetic thermal noise is only related with the thermal motion of the free layer spins. However, we find additional resonance peaks in the magnetic noise spectra, which correspond to the thermal motion of the reference layer spins. Furthermore, the magnetic noise spectra show intricate field dependences, which are related with the spin dynamics of the reference layer induced by spin transfer torque. (C) 2011 Elsevier B. V. All rights reserved.