Correlation between resonance mode crossing and spin torque switching probability in magnetic tunnel junctions

We report on the effect of coupled free- and reference-layer dynamics on switching errors in a spin-torque switched magnetic tunnel junction. Perpendicularly magnetized magnetic tunnel junctions (MTJ) [1-3] are used for this study. The free layer switching speed and probability is related to magnetization dynamics as revealed by spin-torque driven, and thermal fluctuation-driven ferromagnetic resonance (STT- and Thermal-FMR) spectra. We investigate the probability in spin torque driven switching as a function of applied magnetic field, and compare with the STT- and thermal-FMR spectrum in the same field range. A nonmonotonic dependence of the switching probability on field and on bias-voltage is seen, correlating to STT-FMR mode-crossings between the free- and reference-layer spectra-lines. At field values corresponding to the intersections of free- and reference-layer spin wave modes, an increase of errors is observed in switching. Our results show that excitation of the reference layer’s dynamics can affect the MTJ’s net STT-switching probability.
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[2] J. Z. Sun, et. al., J. Appl. Phys. 111, 07C711 (2012)
[3] M. Gajek, et. al., Appl. Phys. Lett. 100, 132408 (2012)