Spin-valve based nanojunctions incorporating Co|Ni multilayers with perpendicular anisotropy were used to study spin-torque driven ferromagnetic resonance (ST-FMR) in a nonlinear regime. Perpendicular field swept resonance lines were measured under a large amplitude microwave current excitation, which produces a large angle precession of the Co|Ni layer magnetization. With increasing rf power the resonance lines broaden and become asymmetric, with their peak shifting to lower applied field. A nonhysteretic step jump in ST-FMR voltage signal was also observed at high powers. The results are analyzed in in terms of the foldover effect of a forced nonlinear oscillator and compared to macrospin simulations. The ST-FMR nonhysteretic step response may have applications in frequency and amplitude tunable nanoscale field sensors.
@article{arxiv.0910.4678,
title = {Spin-torque driven ferromagnetic resonance in a nonlinear regime},
author = {W. Chen and G. de Loubens and J-M. L. Beaujour and J. Z. Sun and A. D. Kent},
journal= {arXiv preprint arXiv:0910.4678},
year = {2009}
}
Comments
4 pages, 3 figures, to appear in Applied Physics Letters