A perspective on nonlinearities in coherent magnetization dynamics

Abstract

The recent thrust in ultrafast magnetization dynamics aims at extending spintronic functionalities to terahertz frequencies. Deterministic manipulation of magnetization at the corresponding ultrashort timescales requires minute control not only over the magnetization itself but also the reservoirs it is interacting with. Although the various intricate couplings between spins, phonons, and electrons-all of which are susceptible to ultrashort laser pulses-lead to many (often nonlinear) coupling routes, magnetization-dynamical nonlinearities have remained largely underexplored. In this Perspective, we highlight recent advances and foresee future developments in the rapidly evolving field of nonlinear magnetization dynamics. Given the elementary character of coherent excitations, we put particular emphasis on their nonlinearities. We briefly review theoretical aspects and assess excitation mechanisms to reach the nonlinear regime of magnetic excitations in a broad class of magnetic materials, such as ferromagnets, antiferromagnets, and ferrimagnets. We present an overview of the groundbreaking experiments that showcase the unique insights provided by magnetic nonlinearities. We conclude by discussing open challenges and opportunities that underpin the potential of nonlinear magnetization dynamics for the advancement of spintronics and cavity quantum electrodynamics with spin waves at terahertz frequencies.

Attosecond magnetization dynamics in non-magnetic materials driven by intense femtosecond lasers

“…It arises from internal spin degrees of freedom of quantum particles 1,2 , and can create complex spin textures, such as skyrmions [3][4][5][6] or other magnetic and topological-ordered phases [7][8][9] . Over the past two decades, immense efforts have been devoted towards the study of ultrafast magnetism, i.e., the manipulation of materials' magnetic structures on femtosecond timescales with ultrashort laser pulses [10][11][12][13][14][15] . However, despite many years of research, numerous open questions remain regarding the mechanisms and pathways that control ultrafast magnetization dynamics [10][11][12][13][14][15][16][17][18][19] .…”

“…Over the past two decades, immense efforts have been devoted towards the study of ultrafast magnetism, i.e., the manipulation of materials' magnetic structures on femtosecond timescales with ultrashort laser pulses [10][11][12][13][14][15] . However, despite many years of research, numerous open questions remain regarding the mechanisms and pathways that control ultrafast magnetization dynamics [10][11][12][13][14][15][16][17][18][19] . Part of the complexity arises because spin dynamics are often entangled with other processes and interactions (because spin is carried by charged particles that also interact with each other and with other particles), and can also evolve over several orders of magnitudes of timescales ranging from femtoseconds to nanoseconds.…”

Magnetoelectrics and multiferroics: theory, synthesis, characterisation, preliminary results and perspectives for all-optical manipulations

“…A change in spin orientation, such as during the precession of spins along the coordinates of a magnon mode, can however change the polarizability of the material. We therefore write the linear polarizability as Taylor expansion of the magnetization (M = S 1 + S 2 ) and Neél vectors (L = S 1 − S 2 ) induced by a magnon mode [25,27,30]:…”

Theory of tensorial Gilbert damping in antiferromagnets

“…The first term in equation ( 1) corresponds to magnetization precession around the effective field H eff , determining the resonance frequency. Such effective field can be calculated from the total energy of the system [13][14][15]. Meanwhile, the second term introduces a viscouslike damping responsible for the linewidth of the resonance.…”