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Angular dependence of spin torque critical currents for CPP-GMR read heads

2005; IEEE Magnetics Society; Volume: 41; Issue: 10 Linguagem: Inglês

10.1109/tmag.2005.855314

1941-0069

N. Smith, J. A. Katine, J. R. Childress, M. J. Carey,

Quantum and electron transport phenomena

This paper derives expressions for the critical current at the onset of spin-transfer-torque (STT) instability in CPP-GMR read heads, as a function of the relative angle (theta) between the free and reference layer magnetizations. Including a general angular dependent STT coefficient B(q=cos(theta)) exclusive of the angular momentum conserving sin(theta) factor, the critical current is found to depend on both B(q) and dB/dq in the non-collinear case |q| < 1. The paper also details the experimental measurement of the angular dependent critical currents on 50-nm sized CPP-GMR devices with synthetic antiferromagnet pinned layers, and fabricated using e-beam lithography. The measurements are consistent with prior theoretical models of the form B(q) ~ 1/[1+cnst*q], and indicate perhaps unanticipated implications for read head operation due to the critical current dependence on dB/dq.