Low Field, Current-Hysteretic Oscillations in Spin Transfer Nanocontacts

TL;DR

This paper reports on low-frequency, hysteretic spin transfer oscillations in nanocontacts, driven by current and magnetic fields, with unique properties such as anharmonicity and persistence at various field strengths.

Contribution

It introduces the observation of low-frequency, anharmonic, hysteretic oscillations in spin valve nanocontacts, highlighting their dependence on current and magnetic field.

Findings

Oscillations occur at zero and low magnetic fields.

Oscillation frequency is below uniform-mode ferromagnetic resonance.

Oscillations are large amplitude, narrowband, and hysteretic.

Abstract

We have measured spin-transfer-driven, large amplitude, current hysteretic, low frequency (< 500 MHz), narrowband oscillations in nanocontacts made to spin valve structures. The oscillations occur in zero field, persist up to 5 mT for in plane applied fields, and to beyond 400 mT for out of plane fields. Unlike previous measurements, the oscillation frequency is well below that for uniform-mode ferromagnetic resonance, is only a weak function of applied field, and is highly anharmonic. The oscillations are hysteretic with applied dc current, appearing at high currents but persisting to lower currents upon decrease of the current. We suggest that these observations are consistent with the dynamics of a nonuniform magnetic state in the vicinity of the contact nucleated by both the spin transfer torque and dc current-generated Oersted fields, with the dynamics driven by spin transfer. The electrical oscillation amplitudes are large and narrowband, with the largest amplitudes on the order of 1 mV and the narrowest linewidths below 1 MHz.