Frequency-tunable low-noise oscillator based on yttrium-iron-garnet/gadolinium-gallium-garnet structure with strong magnetoelastic coupling

We present a frequency-tunable magnetoacoustic oscillator (MAO) that operates in two distinct dynamical regimes. Its core magnetoacoustic resonator comprises a yttrium-iron-garnet (YIG) layer epitaxially grown on a gadolinium-gallium-garnet (GGG) substrate. By optimizing the YIG thickness, we achieve a strong magnetoelastic coupling (approximately 1 MHz) between the YIG ferromagnetic resonance (FMR) and high-overtone bulk acoustic resonances (HBARs) in the 1–2 GHz range. This high coupling strength eliminates the need for bulky components—such as preselectors and circulators—while preserving the ability to lock onto specific acoustic modes. By adjusting the loop overamplification, the MAO can be locked exclusively to the high-quality-factor magnetoacoustic HBARs (low-phase-noise regime) or to both HBARs and the FMR mode (complex regime). In the low-phase-noise regime, the oscillator operates only at specific values of the applied magnetic field and exhibits discrete frequency tuning steps of 3.281 MHz, corresponding to the separation between neighboring HBAR modes. In the complex regime, the involvement of the FMR mode enables continuous frequency tuning, though with phase-noise characteristics that vary depending on the applied-field values. Moreover, in the low-phase-noise regime, the MAO’s phase noise is reduced by 30 dB relative to operation purely on the YIG FMR mode, which agrees with the measured FMR and HBAR <a:math xmlns:a="http://www.w3.org/1998/Math/MathML" display="inline"><a:mi>Q</a:mi></a:math> factors.