RKKY Exchange Bias Mediated Ultrafast All‐Optical Switching of a Ferromagnet

Abstract

The discovery of ultrafast helicity‐independent all‐optical switching (HI‐AOS), as well as picosecond all‐electrical switching of a ferrimagnet, has inspired the ultrafast spintronics community to explore ultrafast switching of a ferromagnet to achieve practical ultrafast storage and memory devices. Two explored mechanisms of HI‐AOS of a ferromagnet in ferromagnet‐ferrimagnet heterostructure are: a) exploiting the indirect exchange coupling with and b) injection of non‐local spin current originated from a switching ferrimagnet. In this manuscript, exchange mediated HI‐AOS of a Ruderman–Kittel–Kasuya–Yosida (RKKY) exchange coupled “[Co/Pt]‐multilayers/Pt spacer/CoGd” heterostructure is demonstrated. The authors have measured layer‐resolved static magnetic properties, single‐shot HI‐AOS, and magnetization dynamics of the ferromagnetic Co/Pt multilayers (MLs), that are ferromagnetically or antiferromagnetically coupled with ferrimagnetic CoGd layers. Time‐resolved magnetization dynamics reveal a 3.5 ps switching time of the Co/Pt MLs, which is the fastest switching of a ferromagnet reported to date. Employing an extended microscopic three‐temperature model, the temporal dynamics of the exchange coupled ferromagnet–ferrimagnet heterostructure are simulated, qualitatively and quantitatively explaining the experimental switching phenomena. This work experimentally as well as theoretically establishes the mechanism of exchange mediated all‐optical switching of ferromagnet‐ferrimagnet heterostructures, which can be integrated with a magnetic tunnel junction for efficient reading after ultrafast energy‐efficient switching.

Global Speed Limit for Finite-Time Dynamical Phase Transition in Nonequilibrium Relaxation

“…Notably, speed limits may also be obtained from "classical" [66][67][68][69][70][71][72] or thermodynamic [68,70,[73][74][75] speed limits which, however, is likely to be more difficult as analytical solutions for probability density functions, in particular at the critical time, do not seem to be feasible. Our findings may provide insight allowing for optimization of ultrafast optical-switching ferromagnetic materials [91]. Finally, our work provokes further intriguing questions, in particular on the microscopic path-wise understanding of the dynamical critical time, the effect of an external field, the existence of heating-cooling asymmetries [19][20][21][22] in different regimes and across phase transitions, and optimal driving protocols [15][16][17][18] that may be relevant for optical-switching ferromagnets.…”

“…Experimentally quenches to negative Jq may be achieved, e.g. by ultrafast optical switching ferro-antiferromagnetic materials [91] or by spinpopulation inversion in metals by radio-frequency irradiation [92] yielding negative spin temperatures [93]. Note that quenches beyond the Néel point (i.e.…”

All-optical control of spin in a 2D van der Waals magnet

“…AOS has been realized principally via thermal processes, such as exchange of angular momentum driven by ultrafast optical heating 4 , 9 – 12 , and preferential domain nucleation and growth driven by magnetic circular dichroism (MCD) 5 , 6 , 13 , 14 , resulting in helicity-independent single-pulse toggle switching, and multipulse helicity-dependent switching, respectively. More recently, switching processes utilizing non-thermal changes to magnetic anisotropy 15 , hot electrons 16 , and interlayer exchange coupling 17 have been explored. Another promising means of manipulating spins with laser pulses is based upon spin-selective charge transfer 18 .…”

Magnetic Configuration Driven Femtosecond Spin Dynamics in Synthetic Antiferromagnets

“…Therefore, engineering and exploiting their tunability will lead to new physics and applications beyond their conventional use as a pinning layer in spin valves and magnetic tunnel junctions . The possibilities range from stabilization of chiral domain walls and skyrmions, spin Seebeck and Peltier effects, and spin-wave polarizer and retarder all the way to AOS. , Besides, SAF particles display a number of desirable characteristics for applications in biological and other fluidic environments …”