Spin Wave Radiation by a Topological Charge Dipole

{ScnGdn} Heterometallic Rings: Tunable Ring Topology for Spin-Wave Excitations

Data carriers using spin waves in spintronic and magnonic logic devices offer operation at low power consumption and free of Joule heating yet requiring noncollinear spin structures of small sizes. Heterometallic rings can provide such an opportunity due to the controlled spin-wave transmission within such a confined space. Here, we present a series of {Sc_nGd_n} (n = 4, 6, 8) heterometallic rings, which are the first Sc-Ln clusters to date, with tunable magnetic interactions for spin-wave excitations. By means of time- and temperature-dependent spin dynamics simulations, we are able to predict distinct spin-wave excitations at finite temperatures for Sc₄Gd₄, Sc₆Gd₆, and Sc₈Gd₈. Such a new model is previously unexploited, especially due to the interplay of antiferromagnetic exchange, dipole-dipole interaction, and ring topology at low temperatures, rendering the importance of the latter to spin-wave excitations.

Flexoresponses of Synthetic Antiferromagnetic Systems Hosting Skyrmions

While strain gradients break lattice centrosymmetry, ferromagnetism is a time-reversal symmetry breaking product. Flexomagnetic effect in ferromagnets is usually indirect and weak. In this Letter, we reveal a topologically enhanced flexomagnetic effect in synthetic antiferromagnetic systems based on Dzyaloshinskii-Moriya interaction and the large deformability of skyrmion. Moreover, the synthetic antiferromagnetic skyrmion exhibits an unexpected Hall effect under strain gradient. We propose that this flexo-Hall effect originates from a geometric Magnus force related to the asymmetric deformation of skyrmion. Our results shed new insights into the flexoresponses in systems hosting topological structures and may open up a new field-"flexoskyrmionics".

Tunable Damping in Magnetic Nanowires Induced by Chiral Pumping of Spin Waves

Spin-current and spin-wave-based devices have been considered as promising candidates for next-generation information transport and processing and wave-based computing technologies with low-power consumption. Spin pumping has attracted tremendous attention and has led to interesting phenomena, including the line width broadening, which indicates damping enhancement due to energy dissipation. Recently, chiral spin pumping of spin waves has been experimentally realized and theoretically studied in magnetic nanostructures. Here, we experimentally observe by Brillouin light scattering (BLS) microscopy the line width broadening sensitive to magnetization configuration in a hybrid metal-insulator nanostructure consisting of a Co nanowire grating dipolarly coupled to a planar continuous YIG film, consistent with the results of the measured hysteresis loop. Tunable line width broadening has been confirmed independently by propagating spin-wave spectroscopy, where unidirectional spin waves are detected. Position-dependent BLS measurement unravels an oscillating-like behavior of magnon populations in Co nanowire grating, which might result from the magnon trap effect. These results are thus attractive for reconfigurable nanomagnonics devices.

Chiral Emission of Exchange Spin Waves by Magnetic Skyrmions

Spin waves or their quanta magnons raise the prospect to act as information carriers in the absence of Joule heating. The challenge to excite spin waves with nanoscale wavelengths free of nanolithography becomes a critical bottleneck for the application of nanomagnonics. Magnetic skyrmions are chiral magnetic textures at the nanoscale. In this work, short-wavelength exchange spin waves are demonstrated to be chirally emitted in a low damping magnetic insulating thin film by magnetic skyrmions. The spin-wave chirality originates from the chiral spin pumping effect and is determined by the cross product of the magnetization orientation and the film normal direction. The Halbach effect explains the enhancement or attenuation of the spin-wave amplitude with a reversed sign of the Dyzaloshinskii-Moriya interaction. Controllable spin-wave propagation is demonstrated by rotating a moderate applied field. Our findings are key for building compact low-power nanomagnonic devices based on intrinsic nanoscale magnetic textures.