Bias and angular dependence of spin-transfer torque in magnetic tunnel junctions

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C. Wang,¹ Y.-T. Cui,¹ J. Z. Sun,² J. A. Katine,³ R. A. Buhrman,¹ and D. C. Ralph¹
¹Cornell University, Ithaca, New York 14853, USA
²IBM T. J. Watson Research Center, Yorktown Heights, New York 10598, USA
³San Jose Research Center, Hitachi Global Storage Technologies, San Jose, California 95135, USA

Received 30 April 2009; published 12 June 2009

Weuse spin-transfer-driven ferromagnetic resonance (ST-FMR) to measure the spin-transfer torquevector in MgO-based magnetic tunnel junctions as a functionof the offset angle between the magnetic moments of theelectrodes and as a function of bias, V. We explainthe conflicting conclusions of two previous experiments by accounting foradditional terms that contribute to the ST-FMR signal at large|V|. Including the additional terms gives us improved precision inthe determination of (V), allowing us to distinguish among competingpredictions. We determine that the in-plane component of d/dV hasa weak but nonzero dependence on bias, varying by 30%–35%over the bias range where the measurements are accurate, andthat the perpendicular component can be large enough to betechnologically significant. We also make comparisons to other experimental techniquesthat have been used to try to measure (V).

URL:	http://link.aps.org/doi/10.1103/PhysRevB.79.224416
DOI:	10.1103/PhysRevB.79.224416
PACS:	76.50.+g; 72.25.-b; 85.75.-d 76.50.+g Ferromagnetic, antiferromagnetic, and ferrimagnetic resonances; spin-wave resonance 72.25.-b Spin polarized transport 85.75.-d Magnetoelectronics; spintronics YEAR: 2009
KEYWORDS:	ferromagnetic resonance, magnesium compounds, magnetic moments, magnetic tunnelling

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