Fundamental mechanism for all-optical helicity-dependent switching of magnetization

Abstract

Switching magnetizations with femtosecond circularly polarized lasers may have revolutionary impacts on magnetic data storage and relevant applications. Achievements in ferrimagnetic and ferromagnetic materials of various structures strongly imply a general phenomenon of fundamental atom-laser interaction. Rotating an atom’s wave function with the rotating electric field of a circularly polarized laser, I show the quantum mechanics for the atom is equivalent to that in a static electric field of the same magnitude and a tremendous static magnetic field which interacts with the atom in somewhat different ways. When some conditions are satisfied, transitions of atoms in these two crossed effective fields lead to a highly nonequilibrium state with orbital magnetic moments inclining to the effective magnetic field. The switching finally completes after the pulse duration via relaxation.

Effect of laser induced orbital momentum on magnetization switching

“…By using the experimental values [4,9], all three estimates yield an angular momentum that are roughly same orders of magnitude, i.e., about δL z ≈ 10 −4 − 10 −3 h per atom. We note that a recently published article [18] claimed that theoretical estimation yields a reasonable magnitude to explain the above experiment; this error was due to mis-identification of the experimental value [19]. Thus, the orbital momentum induced by single laser pulse is not sufficiently large to switch the magnetization of homogeneous magnetic materials.…”

Is perpendicular magnetic anisotropy essential to all-optical ultrafast spin reversal in ferromagnets?

“…Since the beginning of AOS, enormous efforts have been made to develop a reasonably simple theory to explain AOS, and over ten theories have been proposed [11,[21][22][23][24][25][26][27][28][29][30][31][32].…”

“…The traditional spin wave theory only describes spin dynamics under a magnetic or thermal field [20], not a laser field. Since the beginning of AOS, enormous efforts have been made to develop a reasonably simple theory to explain AOS, and over ten theories have been proposed [11,[21][22][23][24][25][26][27][28][29][30][31]32].…”

Theoretical Investigation of Laser Induced Magnetization Reversal by Spin Orbit Coupling and Stimulated Raman Scattering

“…In recent studies, the Rashba effect [26][27][28] is engineered to be coupled to laser schemes [29][30][31]. The circularly polarized laser-induced Rashba effect produces an effective magnetic field on CoPt [31].…”