Spin Torque–Generated Magnetic Droplet Solitons

Magnetic Droplet When a solitary wave travels atop the surface of a fluid, its shape generally changes with time, with some of its components traveling at velocities slightly different than others. In nonlinear media, this spreading effect may be countered by a slimming effect stemming from the non-linearity, which generates an object with perfectly preserved shape, called a soliton. Solitons have been observed in fluids, granular media, and other systems. Mohseni et al. (p. 1295) detected a dissipative soliton (one that also balances gain and dissipation) in a magnetic system, in the form of a magnetic droplet consisting of a core of spins pointing opposite to the external magnetic field. The droplet exhibited peculiar dynamics and could be controlled by electric current. Transport measurements reveal a self-reinforcing traveling wave in a magnetic system. Dissipative solitons have been reported in a wide range of nonlinear systems, but the observation of their magnetic analog has been experimentally challenging. Using spin transfer torque underneath a nanocontact on a magnetic thin film with perpendicular magnetic anisotropy (PMA), we have observed the generation of dissipative magnetic droplet solitons and report on their rich dynamical properties. Micromagnetic simulations identify a wide range of automodulation frequencies, including droplet oscillatory motion, droplet "spinning," and droplet "breather" states. The droplet can be controlled by using both current and magnetic fields and is expected to have applications in spintronics, magnonics, and PMA-based domain-wall devices.

[1]  J. Slonczewski.  Current-driven excitation of magnetic multilayers , 1996 .

[2]  P. Crozat,et al.  Agility of vortex-based nanocontact spin torque oscillators , 2009, 0910.1941.

[3]  John Casimir Slonczewski,et al.  Excitation of spin waves by an electric current , 1999 .

[4]  Ye. Pogoryelov,et al.  Nonlinear frequency and amplitude modulation of a nanocontact-based spin-torque oscillator , 2009, 0910.2819.

[5]  Berger.  Emission of spin waves by a magnetic multilayer traversed by a current. , 1996, Physical review. B, Condensed matter.

[6]  F. Mancoff,et al.  Direct observation of a propagating spin wave induced by spin-transfer torque. , 2011, Nature nanotechnology.

[7]  S. E. Russek,et al.  Frequency modulation of spin-transfer oscillators , 2005 .

[8]  M. Sommacal,et al.  Propagation and control of nanoscale magnetic-droplet solitons , 2012, 1202.3421.

[9]  D. Ralph,et al.  Spin transfer torques , 2007, 0711.4608.

[10]  Justin M. Shaw,et al.  Spin-transfer dynamics in spin valves with out-of-plane magnetized CoNi free layers , 2010 .

[11]  Andrei Slavin,et al.  Spin wave mode excited by spin-polarized current in a magnetic nanocontact is a standing self-localized wave bullet. , 2005, Physical review letters.

[12]  J. Vivanco,et al.  ‡ To whom correspondence should be addressed: , 2022 .

[13]  Mark W. Keller,et al.  Theory for a dissipative droplet soliton excited by a spin torque nanocontact , 2010, 1008.1898.

[14]  M. Hoefer,et al.  Propagating two-dimensional magnetic droplets , 2011, 1111.2310.

[15]  Johan Akerman,et al.  Experimental evidence of self-localized and propagating spin wave modes in obliquely magnetized current-driven nanocontacts. , 2009, Physical review letters.

[16]  J. Miltat,et al.  Spin-torque driven magnetization dynamics : Micromagnetic modeling , 2008 .

[17]  N. Zabusky,et al.  Interaction of "Solitons" in a Collisionless Plasma and the Recurrence of Initial States , 1965 .

[18]  Douady,et al.  From solitary waves to static patterns via spatiotemporal intermittency. , 1993, Physical review letters.

[19]  Sergei Urazhdin,et al.  Direct observation and mapping of spin waves emitted by spin-torque nano-oscillators. , 2010, Nature materials.

[20]  Lane,et al.  Rotating temperature pulse during hydrogen oxidation on a nickel ring. , 1993, Physical review letters.

[21]  Mustapha Tlidi,et al.  On Vegetation Clustering, Localized Bare Soil Spots and Fairy Circles , 2008 .

[22]  Johan Åkerman,et al.  High frequency operation of a spin‐torque oscillator at low field , 2011 .

[23]  Ertl,et al.  Solitons in a surface reaction. , 1991, Physical review letters.

[24]  L. Lugiato,et al.  Cavity solitons as pixels in semiconductor microcavities , 2002, Nature.

[25]  P. Umbanhowar,et al.  Localized excitations in a vertically vibrated granular layer , 1996, Nature.

[26]  Mathias Kläui,et al.  Current-induced domain wall motion in nanoscale ferromagnetic elements , 2011 .

[27]  Three Sources and Three Component Parts of the Concept of Dissipative Solitons , 2008 .

[28]  Kestutis Staliunas,et al.  PATTERN FORMATION AND LOCALIZED STRUCTURES IN DEGENERATE OPTICAL PARAMETRIC MIXING , 1998 .