Coherent elastic excitation of spin waves

Abstract

We model the injection of elastic waves into a ferromagnetic film (F) by a nonmagnetic transducer (N). We compare the configurations in which the magnetization is normal and parallel to the wave propagation. The lack of axial symmetry in the former results in the emergence of evanescent interface states. We compute the energy-flux transmission across the N|F interface and sound-induced magnetization dynamics in the ferromagnet. We predict efficient acoustically induced pumping of spin current into a metal contact attached to F.

Direct observation of magnon-phonon coupling in yttrium iron garnet

“…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.…”

“…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].…”

“…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.…”

“…First, the static lattice distortion induced by the magnetic order may affect the anisotropy of magnon exchange couplings, as seen in the spin waves of iron pnictides with large inplane magnetic exchange anisotropy [5]. Second, the dynamic lattice vibrations interact with time-dependent spin waves may give rise to significant magnon-phonon coupling [6,7]. One possible consequence of such coupling is to create energy gaps in the magnon dispersion at the nominal intersections of the magnon and phonon modes [8,9], as seen in antiferromagnet (Y,Lu)MnO 3 [10].…”

“…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].…”