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 locking 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.
@article{arxiv.1502.03485,
title = {Understanding of phase noise squeezing under fractional synchronization of non-linear spin transfer vortex oscillator},
author = {R. Lebrun and A. Jenkins and A. Dussaux and N. Locatelli and S. Tsunegi and E. Grimaldi and H. Kubota and P. Bortolotti and K. Yakushiji and J. Grollier and A. Fukushima and S. Yuasa and V. Cros},
journal= {arXiv preprint arXiv:1502.03485},
year = {2017}
}