Tunable Short-Wavelength Spin-Wave Emission and Confinement in Anisotropy-Modulated Multiferroic Heterostructures

Abstract

We report on the generation and confinement of short-wavelength spin waves in a continuous film with periodically modulated magnetic anisotropy. The concept, which is demonstrated for strain-coupled Co 40 Fe 40 B 20 =BaTiO 3 heterostructures, relies on abrupt rotation of magnetic anisotropy at the boundaries of magnetic stripe domains. In combination with an external bias field, this modulation of magnetic anisotropy produces a lateral variation of the effective magnetic field, leading to local spin-wave excitation when irradiated by a microwave magnetic field. In domains with small effective field, spin waves are perfectly confined by the spin gap in neighboring domains. In contrast, standing spin waves in domains with large effective field radiate into neighboring domains. Using micromagnetic simulation, we show that the wavelength of emitted spin waves is tunable from a few micrometers down to about 100 nm by rotation of the bias field. Importantly, the orientation of the wave front remains fixed. We also demonstrate that dynamic fluctuations of the effective magnetic field produce exchange-dominated spin waves at singleanisotropy boundaries. The multiferroic heterostructures presented here enable the use of global excitation fields from a microwave antenna to emit tunable spin waves from a nanometer-wide line source at welldefined locations of a continuous ferromagnetic film.

Emission and propagation of 1D and 2D spin waves with nanoscale wavelengths in anisotropic spin textures

“…While the spatial distribution of the domain wall in our experiment is solely a consequence of both dipolar sample confinement fields and magnetostrictive anisotropies, it was shown that further control of the domain wall position can be achieved e.g. by exchange bias patterning [34,39], ferroelectric coupling [21,22], or external magnetic fields [31].…”

Co- and contra-directional vertical coupling between ferromagnetic layers with grating for short-wavelength spin wave generation

“…The possibility of miniaturization of spin-wave-based logic devices is dependent on the wavelength, thus the attention is focused on searching the ways of generation of short SWs. Several approaches has been recently reported: shortening the wavelength in a tapered waveguide [9], microwave-to-SW transducers based either on magnetic wires [10], nanostructure edges [11], diffraction gratings [12][13][14], coplanar waveguides [15] or anisotropy-modulated multiferroic heterostructures [16], transduction of acoustic waves into short SWs due to magneto-elastic coupling [17,18], and emitters based on current-driven oscillating pinned domain walls [19].…”

Optically Inspired Nanomagnonics with Nonreciprocal Spin Waves in Synthetic Antiferromagnets

“…However, the emission of spin waves with sub‐micrometric wavelength is challenging due to the slow spatial decay of the field and the high impedance of the antennas as the size approaches nanoscale dimensions . Ferromagnetic nanostructures, spin‐transfer torque, spin‐orbit torques, spin currents, magnetoelastic coupling, and multiferroic heterostructures are alternative methods used for spin‐wave generation; however, they do not provide a straightforward control of the wavefront and beam shape. Other methods for spatially controlling the spin‐wave propagation include using the natural anisotropy of the spin‐wave dispersion, or physically micro/nanopatterning the spin‐wave medium, but their flexibility and scalability to multi‐beam configurations is limited.…”