ABSTRACT
We investigate experimentally the synchronization of vortex based spin transfer nano-oscillators to an external rf current whose frequency is at multiple integers, as well as at an integer fraction, of the oscillator frequency. Through a theoretical study of the locking mechanism, we highlight the crucial role of both the symmetries of the spin torques and the nonlinear properties of the oscillator in understanding the phase locking mechanism. In the locking regime, we report a phase noise reduction down to -90 dBc/Hz at 1 kHz offset frequency. Our demonstration that the phase noise of these nanoscale nonlinear oscillators can be tuned and eventually lessened, represents a key achievement for targeted radio frequency applications using spin torque devices.
ABSTRACT
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(â¥). Interestingly, we find that our vortex-based oscillator is quasi-isochronous independently of H(â¥) and for a dc current ranging between 18 and 25 mA. It means that the severe nonlinear broadening usually observed in STNOs can be suppressed on a broad range of bias. Still, the generation linewidth displays strong variations on H(â¥) (from 40 kHz to 1 MHz), while the frequency tunability in current remains almost constant (7 MHz/mA). This demonstrates that isochronicity does not necessarily imply a loss of frequency tunability, which is here governed by the current induced Oersted field. It is not sufficient either to achieve the highest spectral purity in the full range of H(â¥). 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.
ABSTRACT
The discovery of the spin-torque effect has made magnetic nanodevices realistic candidates for active elements of memory devices and applications. Magnetoresistive effects allow the read-out of increasingly small magnetic bits, and the spin torque provides an efficient tool to manipulate - precisely, rapidly and at low energy cost - the magnetic state, which is in turn the central information medium of spintronic devices. By keeping the same magnetic stack, but by tuning a device's shape and bias conditions, the spin torque can be engineered to build a variety of advanced magnetic nanodevices. Here we show that by assembling these nanodevices as building blocks with different functionalities, novel types of computing architecture can be envisaged. We focus in particular on recent concepts such as magnonics and spintronic neural networks.
ABSTRACT
CONCLUSIONS: In our study, pedicled nasal flap (NF) did not provide better results than free nasal graft (NG) for primary closure of cerebrospinal fluid (CSF) rhinorrhea. In the future, a multicenter randomized study would be needed to confirm this result. The choice of surgical technique will depend on the surgeon's experience, and the position and size of the defect. OBJECTIVES: To evaluate our results in repairing CSF leaks, comparing the two techniques we used: free NG and pedicled NF. METHODS: A total of 33 patients diagnosed with CSF rhinorrhea were operated on between June 2000 and May 2010; 17 were women. The mean age was 44.7 years (± 13.0). Twenty-two (66.6%) NFs of the middle and lower turbinate and septum were performed, the rest being NGs of the middle and lower turbinate only. A descriptive statistical analysis and a Kaplan-Meier survival analysis were carried out and the log-rank statistic was used to compare both techniques. RESULTS: In the present study, 78% of defects were closed in all cases; NF was used in 86% (19) and NG in 63.63% (7). The mean follow-up was 71.5 (95% confidence interval (CI), 56.9-86.1) months. There were no statistically significant differences (p > 0.05).
