Nonlinear and chaotic magnetization dynamics near bifurcations of the Landau-Lifshitz-Gilbert equation

Magnetization switching in bistable nanomagnets by picosecond pulses of surface acoustic waves

“…The key point is tuning the height of the potential barrier between the metastable energy minima using weak magnetic fields easily accessible in the experiments. Our geometry, where the magnetic nanoparticle is driven by short SAW pulses, is complementary to similar objects driven by quasi-monochromatic excitations and displaying bifurcations and chaos [27]. Ultimate speed limits of the magneto-acoustic switching can be investigated solving the LLG equations (7-12) driven by dynamic SAW strains in Eq.…”

“…Here we propose an in-plane architecture of a bistable magnetic system, where the magnetization can be switched by relatively weak ultrashort pulses of surface acoustic transients under the presence of a small external magnetic field. Interestingly, a similar generic system consisting of an elliptical nanoparticle driven by an oscillating magnetic field (under the static magnetic bias) has been investigated recently with the main focus on interplay between magnetization switching, quasiperiodicity and chaos [27,28]. An ultralow energy threshold for single bit magnetization recording down to the ultimate Landauer limit [29] stimulated some recent experimental studies in ensembles of nanomagnets [30], isolated nanomagnets [31] and single atoms [32].…”

Magnetization reversal driven by low dimensional chaos in a nanoscale ferromagnet

“…Recent theoretical work has shown that interesting magnetization dynamics can also manifest in a uniformly magnetized domain under large ac external fields in ways that are not chaotic 19,62 . It has been shown that large ac drive can lead to large enhancements of transient behavior times as well as a different kind of magnetization reversal where a dynamic state with magnetization opposite to the applied dc field is achieved.…”

“…First, the phenomena we observe has a monotonic threshold behavior as a function of drive amplitude, while the effect reported in refs. 19,62 is non-monotonic. Second, the magnetization reversal achieved by our mechanism on the bistable magnetization is persistent upon removing ac drive (up to thermal activation time scales), while the dynamic reversed state achieved by the other mechanism is not.…”

“…Geometric confinement discretizes the spectrum of spin wave eigenmodes in a nanomagnet and thereby suppresses energy- and momentum-conserving nonlinear spin wave interactions present in bulk ferromagnets with continuous spin wave spectrum 19 . This suppression of nonlinear spin wave interactions allows for excitation of large-amplitude quasi-uniform precession of magnetization without simultaneous excitation of other spin wave modes of the system 20,21 .…”