Direct observation of closure domain wall mediated spin waves

Abstract

The generation and guiding of spin waves from and by magnetic domain walls are demonstrated. The spin waves radiate from pinned and oscillating magnetic closure domain walls and propagate linearly along a narrow path formed by the surrounding 180° asymmetric Bloch domain walls. The propagating spin wave modes are directly visualized by time-resolved magneto-optical Kerr microscopy with picosecond temporal resolution. A linear relationship between excitation frequency, wavelength, and number of spin waves per domain exists. Independent of the field excitation frequency, a constant phase velocity of spin waves propagation is obtained. Spin waves characteristics can be tuned by varying the magnetic domain dynamics, allowing for variable spin wave characteristics with magnetic field characteristics and histories.

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

“…The wavelength of emitted spin waves from these pointlike sources is roughly twice the nano-oscillator or laser spot size. Topological defects in magnetic films such as vortices and domain walls provide another means of local spin-wave emission [11][12][13]. Pinned magnetic domain walls in magnetic nanowires that are brought into oscillation by a microwave spin-polarized current, for instance, allow for monochromatic spin-wave emission up to high frequency [12].…”

Theory of linear spin wave emission from a Bloch domain wall

“…Recently, there have also been numerical [10,11] and experimental [12,13] reports of pinned domain walls generating spin waves, with wavelengths down to tens of nanometers [14]. The origin of the observed spin wave emission has typically been attributed to the domain wall oscillations, generated by the applied microwave magnetic field [10][11][12][13] or spin-polarized current [14,15].…”

“…Recently, there have also been numerical [10,11] and experimental [12,13] reports of pinned domain walls generating spin waves, with wavelengths down to tens of nanometers [14]. The origin of the observed spin wave emission has typically been attributed to the domain wall oscillations, generated by the applied microwave magnetic field [10][11][12][13] or spin-polarized current [14,15].In this letter, we report an analytical theory that demonstrates emission of exchange spin waves from a Bloch domain wall driven by a uniform microwave magnetic field, as a result of a linear process. The problem is reduced to that of the Pöschl-Teller potential in a Schrödinger-like equation -an exactly solvable model, of particular interest in quantum mechanics [16] and optics [17,18].…”

Advanced magneto-optical microscopy: Imaging from picoseconds to centimeters - imaging spin waves and temperature distributions (invited)

“…The possibility of generating spin waves from domain wall oscillations along a magnetic path constricted by 180 • domain walls was discussed in detail in Ref. 15, where the tuning of the wavelength of spin waves by varying the excitation field frequency is investigated and imaged by time-resolved MOKE microscopy.…”

“…The spin waves can be excited by different means, for instance not only by using microwave antennas, 14 but also from domain wall oscillations 15,16 and magnetic vortex reversal. 17 Here, we present a proof of the generation of spin waves from flux-closed vortex configuration via time-resolved MOKE imaging.…”