Frequency multiplication by collective nanoscale spin-wave dynamics

Abstract

Frequency multiplication is a process in modern electronics in which harmonics of the input frequency are generated in nonlinear electronic circuits. Devices based on the propagation and interaction of spin waves are a promising alternative to conventional electronics. The characteristic frequency of these excitations is in the gigahertz (GHz) range and devices are not readily interfaced with conventional electronics. Here, we locally probe the magnetic excitations in a soft magnetic material by optical methods and show that megahertz-range excitation frequencies cause switching effects on the micrometer scale, leading to phase-locked spin-wave emission in the GHz range. Indeed, the frequency multiplication process inside the magnetic medium covers six octaves and opens exciting perspectives for spintronic applications, such as all-magnetic mixers or on-chip GHz sources.

Imaging and phase-locking of non-linear spin waves

“…This behavior is a hallmark of the amplitude-phase-oscillations expected for non-linear processes at low bias fields 38 . While the integer multiples 13 , 16 cover a field range as broad as the ferromagnetic resonance line shape, the odd half-integer harmonics are restricted to a very narrow field window in which they emerge coherently. Using additional micromagnetic simulations for a comparable sample geometry we find, that the additional half-integer multiples with integer index n indeed arise from the precessional motion, spanning a frequency comb n ⋅f rf /2 with amplitudes matching the experimental results, as shown Fig.…”

“…For example, in three-magnon scattering 5 , 6 typically the excitation of a uniform magnon leads to scattering into a magnon pair at half of the driving frequency with opposing wave vectors 7 – 9 . In addition, four magnon scattering processes 4 , 10 – 12 may be used for harmonic generation 13 – 16 or the amplification and stabilization of propagating spin waves 17 . Besides frequency conversion effects, non-linear magnon-scattering processes are potentially also suitable for short wavelength spin-wave generation.…”

Filtering and Imaging of Frequency-Degenerate Spin Waves Using Nanopositioning of a Single-Spin Sensor

“…The NV spin allows probing spin-wave spectra with a ∼1-MHz frequency resolution through spin lifetime measurements and characterizing spin-wave amplitudes by measuring the NV spin rotation rate . Recently, NV magnetometry has been used to study domain-wall-guided spin-wave modes, magnon scattering, − spin chemical potentials, and frequency combs . To enable sensitivity to target spin-wavelengths, accurate control of the NV-sample distance is crucial because the spin-wave stray fields depend exponentially on the distance to the sample at a length scale set by their wavelength.…”

“… 11 Recently, NV magnetometry has been used to study domain-wall-guided spin-wave modes, 12 magnon scattering, 13 − 15 spin chemical potentials, 16 and frequency combs. 17 To enable sensitivity to target spin-wavelengths, accurate control of the NV-sample distance is crucial because the spin-wave stray fields depend exponentially on the distance to the sample at a length scale set by their wavelength.…”

Filtering and imaging of frequency-degenerate spin waves using nanopositioning of a single-spin sensor

“…The NV spin allows probing spin-wave spectra with a ∼1-MHz frequency resolution through spin lifetime measurements and characterizing spin-wave amplitudes by measuring the NV spin rotation rate [11]. Recently, NV magnetometry has been used to study domain-wall-guided spin-wave modes [12], magnon scattering [13][14][15], spin chemical potentials [16], and frequency combs [17]. To enable sensitivity to target spin-wavelengths, accurate control of the NV-sample distance is crucial because the spin-wave stray fields depend exponentially on the distance to the sample at a length scale set by their wavelength.…”