Chiral excitation of spin waves in ferromagnetic films by magnetic nanowire gratings

Abstract

We theoretically investigate the interlayer dipolar and exchange couplings for an array of metallic magnetic nanowires grown on top of an extended ultrathin yttrium iron garnet film. The calculated interlayer dipolar coupling agrees with observed anticrossings [Chen et al., Phys. Rev. Lett. 120, 217202 (2018)], concluding that the interlayer exchange coupling is suppressed by a spacer layer between the nanowires and film. The Kittel mode in the nanowire array couples chirally to spin waves in the film, even though Damon-Eshbach surface modes do not exist. The chirality is suppressed when the interlayer exchange coupling becomes strong.In the experiments, a coplanar waveguide on top of the NWA|YIG system of Fig. 1 is tuned to the NWA Kittel mode, in which the magnetization of all wires precesses in phase. Due to the large magnetization and form anisotropy of Co and Ni, this frequency is much higher arXiv:1901.09182v1 [cond-mat.mes-hall]

Chiral Spin-Wave Velocities Induced by All-Garnet Interfacial Dzyaloshinskii-Moriya Interaction in Ultrathin Yttrium Iron Garnet Films

“…2 exhibit a clear amplitude nonreciprocity. The nonreciprocity parameter β = S12−S21 S12+S21 [47] is extracted as a function of θ ( Fig. 4(d)).…”

Unidirectional Pumping of Phonons by Magnetization Dynamics

“…It can be measured by Brillouin light scattering [18], the spin-rotation coupling by fabricating a conductor on top of the acoustic medium [15,16], and other techniques [52]. The generation of unidirectionality by interference does not require a nonreciprocal coupling mechanism [25][26][27][28] but only an out-of-phase relation of the two fields at resonance. The phenomenon should be universal for many field propagation phenomena, such as exchange coupled magnetic nanowires and films [25] and reciprocally coupled magnons and waveguide photons [28].…”

“…1. Similar configurations on magnetic substrates led to the electrical detection of diffuse magnon transport [22,23] and discovery of nonreciprocal magnon propagation [24], i.e., the generation of a unidirectional spin current in half space [25,26]. Magnetic stray fields of the magnetization dynamics also generate chiral electron [27] and waveguide photon [28] transport.…”

“…where M ¼ ðM x ; M y ; M z Þ T is the magnetization vector and the demagnetization constants are taken as N xx ≃d=ðdþwÞ and N zz ≃ w=ðd þ wÞ [25]. Although the predicted effects are classical, we use a quantum description for convenience and future applications in quantum phononics [3][4][5][6]38]; we can always recover the classical picture by replacing operators by amplitudes.…”

Magnon trap by chiral spin pumping

“…Magnons, the elementary excitations of the magnetic order, carry an intrinsic angular momentum that can be utilized to transport information [7][8][9][10]. Dynamic dipolar stray fields emitted by ferromagnetic nanostructures can generate a unidirectional magnon current in a ferromagnetic film or conductors in its proximity by "chiral spin pumping" [11][12][13][14][15]. Magnons can propagate over centimeters [16] in magnetic insulators such as yttrium iron garnet (YIG) without Joule heating.…”