All-optical observation and reconstruction of spin wave dispersion

Abstract

To know the properties of a particle or a wave, one should measure how its energy changes with its momentum. The relation between them is called the dispersion relation, which encodes essential information of the kinetics. In a magnet, the wave motion of atomic spins serves as an elementary excitation, called a spin wave, and behaves like a fictitious particle. Although the dispersion relation of spin waves governs many of the magnetic properties, observation of their entire dispersion is one of the challenges today. Spin waves whose dispersion is dominated by magnetostatic interaction are called pure-magnetostatic waves, which are still missing despite of their practical importance. Here, we report observation of the band dispersion relation of pure-magnetostatic waves by developing a table-top all-optical spectroscopy named spin-wave tomography. The result unmasks characteristics of pure-magnetostatic waves. We also demonstrate time-resolved measurements, which reveal coherent energy transfer between spin waves and lattice vibrations.

Magnon polarons in the spin Peltier effect

“…By the MEC, magnons and phonons, in the vicinity of the crossings of their dispersion relations, are hybridized into quasiparticles called magnon polarons that share mixed magnonic and phononic characters [6,8,[10][11][12][20][21][22][23][24][25][26][27][28][29][30]. Magnon polarons can convey spin information with velocities close to those of phonons, much faster than the magnon velocities in the dipolar magnon regime [7,8,14,15]. Besides, thanks to the long-lived phononic constituent, magnon polarons may have longer lifetimes than pure magnons and can enhance the spin-current related phenomena, such as the spin Seebeck effect [10-12, 17, 21-23, 29] and spin pumping [20].…”

Measurement of transient strain induced by two-photon excitation

“…Since these oxides have large band gaps, the processes are thought to proceed without absorption, and the generation of phonons is not always mentioned as a mechanism to drive spins. In some materials hybrid magnetoelastic modes are identified as the relevant excitations [24,25]. Among the magnetic oxides, yttrium iron garnet (YIG) provides the lowest magnon * bargheer@uni-potsdam.de damping.…”

Recent advances in mechanical torque studies of small-scale magnetism

“…A single experiment has shown indications of more than one aspect of the physics discussed above. Hashimoto et al [132] have developed an all-optical method they term spin-wave tomography, which detects broadband magnons and phonons launched in a ferrimagnetic garnet film through absorption of an ultrafast laser pulse. The excited modes are resolved in dispersion, (k, ω), and as a function of time delay, through reconstructions of the diffractive Faraday effect imprints on transmitted probe pulses that are polarization-analyzed and imaged with a camera [132].…”