ترغب بنشر مسار تعليمي؟ اضغط هنا

Tunability versus deviation sensitivity in a non-linear vortex oscillator

149   0   0.0 ( 0 )
 نشر من قبل Sylvain Martin
 تاريخ النشر 2013
  مجال البحث فيزياء
والبحث باللغة English
 تأليف S.Y. Martin




اسأل ChatGPT حول البحث

Frequency modulation experiments were performed on a spin torque vortex oscillator for a wide range of modulation frequency, up to 10 % of the oscillator frequency. A thorough analysis of the intermodulation products shows that the key parameter that describes these experiments is the deviation sensitivity, which is the dynamical frequency-current dependence. It differs significantly from the oscillator tunability discussed so far in the context of spin-transfer oscillators. The essential difference between these two concepts is related to the response time of the vortex oscillator, driven either in quasi-steady state or in a transient regime.



قيم البحث

اقرأ أيضاً

109 - S. Martin 2011
Radiofrequency vortex spin-transfer oscillators based on magnetic tunnel junctions with very low resistance area product were investigated. A high power of excitations has been obtained characterized by a power spectral density containing a very shar p peak at the fundamental frequency and a series of harmonics. The observed behaviour is ascribed to the combined effect of spin transfer torque and Oersted-Amp`ere field generated by the large applied dc-current. We furthermore show that the synchronization of a vortex oscillation by applying a ac bias current is mostly efficient when the external frequency is twice the oscillator fundamental frequency. This result is interpreted in terms of a parametric oscillator.
We investigate experimentally the synchronization of a vortex based spin transfer oscillator to an external rf current whose frequency is at multiple integers, as well as half integer, of the oscillator frequency. Through a theoretical study of the l ocking process, we highlight both the crucial role of the symmetries of the spin torques acting on the magnetic vortex and the nonlinear properties of the oscillator on the phase locking process. Through the achievement of a perfect injection locking state, we report a record phase noise reduction down to -90dBc/Hz at 1 kHz offset frequency. The phase noise of these nanoscale oscillators is demonstrating as being low and controllable which is of significant importance for real applications using spin transfer devices.
Harnessing chaos or intrinsic nonlinear behaviours from dynamical systems is a promising avenue for the development of unconventional information processing technologies. However, the exploitation of such features in spintronic devices has not been a ttempted despite the many theoretical and experimental evidence of nonlinear behaviour of the magnetization dynamics in nanomagnetic systems. Here, we propose a first step in that direction by unveiling and characterizing the patterns and symbolic dynamics originating from the nonlinear chaotic time-resolved electrical signals generated experimentally by a nanocontact vortex oscillator (NCVO). We use advanced filtering methods to dissociate nonlinear deterministic patterns from thermal fluctuations and show that the emergence of chaos results in the unpredictable alternation of simple oscillatory patterns controlled by the NCVOs core-polarity switching. With phase-space reconstruction techniques, we perform a symbolic analysis of the time series to assess the level of complexity and entropy generated in the chaotic regime. We find that at the centre of its incommensurate region, it can exhibit maximal entropy and complexity. This suggests that NCVOs are promising nonlinear nanoscale source of entropy that could be harnessed for information processing.
We investigate the spectral characteristics of spin torque oscillator (STO) excited by the spin Hall-induced spin current. We observe that the modest spin current injection triggers the conventional single peak oscillating behavior of STO. As the spi n current is further increased to enter the non-linear regime, we find the transition of the spectrum from a single peak to multipeak structure whose frequency spacing is constant. This behavior can be primarily explained by the extremely broadened peak of the STO, which is accompanied by the frequency-dependent filtering by the transmission line. To explain the observation more quantitatively, we also discuss that the multipeak may reflect the characteristics of the intrinsic dynamics of STO in the non-linear regime.
286 - A. Hamadeh 2013
We investigate the microwave characteristics of a spin transfer nano-oscillator (STNO) based on coupled vortices as a function of the perpendicular magnetic field $H_perp$. While the generation linewidth displays strong variations on $H_perp$ (from 4 0 kHz to 1 MHz), the frequency tunability in current remains almost constant (~7 MHz/mA). We demonstrate that our vortex-based oscillator is quasi-isochronous independently of $H_perp$, so that the severe nonlinear broadening usually observed in STNOs does not exist. Interestingly, this does not imply a loss of frequency tunability, which is here governed by the current induced Oersted field. Nevertheless this is not sufficient to achieve the highest spectral purity in the full range of $H_perp$ either: we show that the observed linewidth broadenings are due to the excited mode interacting with a lower energy overdamped mode, which occurs at the successive crossings between harmonics of these two modes. These findings open new possibilities for the design of STNOs and the optimization of their performance.
التعليقات
جاري جلب التعليقات جاري جلب التعليقات
سجل دخول لتتمكن من متابعة معايير البحث التي قمت باختيارها
mircosoft-partner

هل ترغب بارسال اشعارات عن اخر التحديثات في شمرا-اكاديميا