https://doi.org/10.1140/epjb/e2011-20505-3
Regular Article
Analysis of magnetization instability patterns in spin-transfer nano-oscillators
1
Laboratorio di Meccatronica, Politecnico di Torino, 11029 Verrès,
Aosta,
Italy
2
Dip. Tecnologie, Università “Parthenope”,
80143
Napoli,
Italy
3
INRIM – Istituto Nazionale di Ricerca Metrologica,
10135
Torino,
Italy
4
Dip. Ing. Elettrica, Università “Federico II”,
80125
Napoli,
Italy
5
ECE Dept., UMIACS, AppEl Center, University of
Maryland, College
Park
MD
20742,
USA
a e-mail: bonin.roberto@gmail.com
Received:
23
June
2011
Received in final form:
2
December
2011
Published online:
30
January
2012
The stability of large precessional magnetization motions induced by spin-polarized currents in spin-transfer nano-oscillators is discussed. Quantitative analytical predictions are obtained for the critical values of spin-polarized injected current and external magnetic field at which the oscillator magnetization precession becomes unstable. It is shown that the mechanism leading to instability is parametric resonance of well-defined pairs of magnetostatically coupled perturbation modes. The amplitude of these modes grows to large non-thermal values when the oscillator frequency matches the mean of the natural frequencies of the two coupled modes. Analytical predictions are obtained for the space-time structure and symmetry of the magnetization patterns that are formed at the instability. Analytical results are compared with numerical simulations of spin-transfer-driven magnetization dynamics.
Key words: Mesoscopic and Nanoscale Systems
© EDP Sciences, Società Italiana di Fisica and Springer-Verlag, 2012