Laser-Induced Spatiotemporal Dynamics of Magnetic Films

Abstract

We present a theory for the coherent magnetization dynamics induced by a focused ultrafast laser beam in magnetic films, taking into account nonthermal (inverse Faraday effect) and thermal (heating) actuation. The dynamic conversion between spin waves and phonons is induced by the magnetoelastic coupling that allows efficient propagation of angular momentum. The anisotropy of the magnetoelastic coupling renders characteristic angle dependences of the magnetization propagation that are strikingly different for thermal and nonthermal actuation.

Direct observation of magnon-phonon coupling in yttrium iron garnet

“…While our findings of a novel magnon-phonon coupling at zero field are consistent with the formation of magnonpolarons in YIG [6,7], they are not direct proof that magnon-polaron formation alone causes anomalous features in the magnetic field and temperature dependence of the SSE. Other effects, such as spin diffusion length, acoustic quality of the YIG film, and magnon spin conductivity also play an important role in determining the SSE anomaly [41].…”

“…In both cases, we expect the integrated intensity of hybridized excitations at the intersecting points to be the sum of separate magnon and phonon scattering intensity without spin-lattice coupling [8]. Finally, if magnon and phonon lifetime-broadening is smaller than their interaction strength, the resulting mixed quasiparticles can form magnon polarons [6,7].Here we use inelastic neutron scattering to study lowenergy ferromagnetic magnons and acoustic phonons in the ferrimagnetic insulator yttrium iron garnet (YIG) with chemical formula -14]. At zero field and 100 K, we confirm the quadratic wave vector dependence of the magnon energy, E = Dq 2 , where D is the effective spin wave stiffness constant and q is momentum transfer (inÅ −1 or 10 10 m −1 ) away from a Bragg peak [ Fig.…”

“…Since the energy of the magnon should increase with increasing magnetic field, the field independent nature of the peak position in Fig. 4(b) suggests that the mode cannot be a simple addition of magnon and phonon, but most likely arises from hybridized magnon polarons [6,7]. Figure 4(d) shows the full width at half maximum (FWHM) of the magnon width at 0 T and 9.1 T. Within the errors of our measurements, we see no energy width change in the measured wave vector region.…”

“…When the applied field is larger than the critical field, the magnon dispersoin is separated from the TA/LA phonon modes. In the theory of hybrid magnon-phonon excitations [6,7], the SSE anomalies occur at magnetic fields and wave vectors at which the phonon dispersion curves are tangents to the magnon dispersion, where the effects of the magnon-phonon coupling are maximized [40].…”

Vibrations of magnetization under the shock influence of elastic displacement.

“…Особый интерес представляют такие процессы в средах, обладаю-щих магнитным упорядочением [1]. Для их исследования используется метод «накачки-зонда», когда возмущение намагниченности создается мощным лазе-ром (обычно пико-или фемтосекундным), а ее считывание -другим маломощ-ным лазером по эффекту Фарадея или Керра [2,3]. Мощный импульс света нагревает магнитную среду, в результате чего в ней возникают упругие напря-жения волнового характера [4][5][6], через посредство магнитострикции вызыва-ющие изменение намагниченности, в том числе прецессию резонансного харак-тера [7,8] …”