Microwave generation in MgO magnetic tunnel junctions due to spin transfer effects (invited)

Low resistance-area product and high spin polarization lead to current-driven precession of the magnetization in CoFeB/MgO/CoFeB magnetic tunnel junctions due to spin-transfer torque (STT) effects. Current-driven precession of the magnetization leads to pronounced narrow peaks in the frequency range of 4-7 GHz with a full width at half maximum as low as 21 MHz. The peak amplitudes have a threshold dependence on the dc bias current. Experimental results show that the STT-driven microwave generation can also occur in MgO-based junctions at maximum resistance state but at opposite current polarity, which corresponds to precession of the magnetization of the reference layer (RL) electrode. This conclusion is supported by the peak frequency dependence on magnetic field. The maximum generated power was 35 nW at a peak frequency of about 6 GHz. The estimated maximum angle change of the RL in-plane magnetization rotation is 19 degrees and corresponds to a large angle precession. (c) 2008 American Institute of Physics.