[Todos] Lunes 24/08 11 hs. - Marina Tortarolo - Seminario del Depto. de Mat. Condensada

[Solange Di Napoli]

                    Ciclo de Seminarios 2015
                 Departamento de Materia Condensada
                       GIyA, Tandar, CAC-CNEA.


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                  Sincronización de osciladores de spin torque

                            Marina Tortarolo

Departamento de Física de la Materia Condensada, GIyA - CNEA.


SEMINARIO: LUNES 24 de Agosto, 11 hs. Aula Nivel 0.

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                            RESUMEN

Spin transfer oscillations (STOs)[1,2] are promising for microwave
applications due to their wide frequency tunning range vs. current, fast
modulation rates and  compatibility with nanoelectronics. Nevertheless,
one of the main issues for these STOs is their relative large linewidth,
which can be reduced by phase-locking several oscillators together. For
this, we studied the synchronization of an STO to a microwave signal for
standard in-plane magnetized oscillators, for which an in-plane precession
(IPP) mode is stabilized. The injection locking of this IPP mode to an
external microwave current was demonstrated by experiments to occur only
at two times the generated frequency (2f) [3]. However, the linewidth in
the locked regime was reduced only by a factor of ten, while a reduction
to the linewidth of the source was expected. This raises the question on
the role of noise on the phase-locking, which leads us toinvestigate the
phase noise and the transient behavior to the locked state for 2f
synchronization.
The numerical analysis of the phase noise in the synchronized state
predicts a crossover from a 1/f2 (random walk)dependence for frequency
locking to a 1/f0(white noise)for phase locking upon increasing microwave
current, indicating a truly phase locked state. Experimentally we found
for MTJ nanopillars that while a complete synchronization is achieved in
the frequency, the system is not in a truly phase locked regime.
In order to understand the effects of thermal fluctuations in the
synchronized state, we derived from the KTS model[4] an analytical
expression for the transient state for the  IPP mode. As seeing at f[5],
it was found that at 2f the phase approaches its locked state
exponentially and oscillating above a critical microwave current.The
correlation between the transient behavior and the phase noise will be
discussed.

[1] J. C. Slonzewski, J. Magn. Magn. Mater. 159 L1 (1996)
[2] L. Berger, Phys. Rev. B 54, 9353 (1996)
[3] Quinsat et al., App. Phys. Lett 97, 182507 (2010)
[4] A. Slavin and V. Tiberkevich, IEEE Transactions in Magnetics, Vol. 45,
NO. 4 (2009)
[5]Y. Zhou et al, Phys. Rev. B82, 012408 (2010)


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-- 
Solange Di Napoli
Depto. de Fisica CNEA-CAC
Avda. Gral Paz 1499 - (CP.1650)
San Martin, Bs.As. - Argentina
PHONE: (54) 11 6772 7657
FAX #: (54) 11 6772 7121
email: dinapoli en tandar.cnea.gov.ar
        dinapoli en df.uba.ar