Mutual phase-locking of microwave spin torque nano-oscillators

Abstract

The spin torque effect that occurs in nanometre-scale magnetic multilayer devices can be used to generate steady-state microwave signals in response to a d.c. electrical current. This establishes a new functionality for magneto-electronic structures that are more commonly used as magnetic field sensors and magnetic memory elements. The microwave power emitted from a single spin torque nano-oscillator (STNO) is at present typically less than 1 nW. To achieve a more useful power level (on the order of microwatts), a device could consist of an array of phase coherent STNOs, in a manner analogous to arrays of Josephson junctions and larger semiconductor oscillators. Here we show that two STNOs in close proximity mutually phase-lock-that is, they synchronize, which is a general tendency of interacting nonlinear oscillator systems. The phase-locked state is distinct, characterized by a sudden narrowing of signal linewidth and an increase in power due to the coherence of the individual oscillators. Arrays of phase-locked STNOs could be used as nanometre-scale reference oscillators. Furthermore, phase control of array elements (phased array) could lead to nanometre-scale directional transmitters and receivers for wireless communications.

Micromagnetic simulations of magnetization dynamics in a nanowire induced by a spin-polarized current injected via a point contact

“…Practical applications of spin torque nano-oscillators (STNOs) require high output power levels and low phase noise 8,9,10 . Several approaches pursuing these goals, such as phase locking of arrays of STNOs 11,12,13,14 and development of STNOs based on magnetic tunnel junctions 15,16,17,18 are active areas of research.…”

“…The two-dimensional systems offer the advantage of phase locking of nearby STNOs via interaction by spin waves propagating in the common ferromagnetic free layer 11,12 . The phase locking regime is attractive from the practical point of view because the output power of STNOs increases and their phase noise decreases in this regime 11,12,13 .…”

“…Up to date, two major STNO geometries have been studied: (i) spin valve nanopillars in which propagation of magnetic excitations is restricted by the ferromagnet boundaries in all three spatial dimensions (zero-dimensional systems, 0D) 5,27,28 and (ii) point contacts to spin valves in which magnetic excitations can propagate in the plane of the spin valve (twodimensional systems, 2D) 6,8,11,12,29 . The two-dimensional systems offer the advantage of phase locking of nearby STNOs via interaction by spin waves propagating in the common ferromagnetic free layer 11,12 .…”

Micromagnetic simulations of cylindrical magnetic nanowires

“…The ordered arrays of multilayered cylindrical nanowires is also very attractive for application in new generation of the microwave devices based on arrays of the spin-torque nanooscillators (Kiselev, 2003;Kaka, 2005;Dussaux, 2010). It has been shown by micromagnetic simulation of multilayered Co/Cu/Co nanowires (Abreu Araujo, 2012) that depending on the field amplitude and the injected dc current, a particular magnetic configurations appear, involving either a one-vortex state or a two-vortex magnetic state.…”

Self-consistent calculation of spin transport and magnetization dynamics

“…These types of current-induced magnetization dynamics could potentially find use in novel functional spintronic devices [15] such as magnetic random access memories (MRAMs) [16], microwave oscillators [17,18], domain wall storage devices [19], and spin wave logic devices [20].…”