Multiple three-magnon splittings in bismuth yttrium iron garnet nanostructures

Abstract

We experimentally demonstrate the generation of multiple three-magnon splitting processes in an in-plane magnetized submicron Bi-YIG disk using micro-focused Brillouin light scattering. The low magnetic damping and strong magneto-optical response of BiYIG enable the detection of nonlinear spin-wave interactions at low threshold powers. By tuning the in-plane static magnetic field, excitation frequency, and power, we observe the generation of three pairs of secondary modes symmetrically distributed around half the excitation frequency. Time-resolved BLS measurements present temporal dynamics and threshold behavior associated with the successive activation of three-magnon pairs.

Figures (5)

• Figure 1: Experimental setup. (a) BiYIG sample is characterized using $\mu$-BLS while applying in-plane static field to get an in-plane magnetized state. (b) The laser spot is focused on the disk center. (c) Thermal BLS spectra as a function of in-plane static magnetic field, varied from 7 mT to 25 mT in steps of 1 mT.
• Figure 2: (a) The BLS spectra were measured as the excitation frequency changed for each field, with the power set at 5 dBm. The mode that was excited is denoted as f. (b) Time-resolved BLS measurements at 14 mT showing the temporal evolution of the spin-wave intensity for the excited mode at 2.46 GHz (solid line) and the secondary modes of three magnon splitting at $f/2-\delta=1.12$ GHz (dashed line) and $f/2+\delta=1.3$ GHz (dotted line).
• Figure 3: BLS spectra measured at an in-plane static magnetic field of 14 mT for excitation frequencies ranging from 2.70 GHz to 2.95 GHz at a constant r.f. power of 9 dBm. (b) BLS spectra at 2.84 GHz and 9 dBm (blue) compared to the thermal level (red).
• Figure 4: Temporal evolution of the excited mode at 2.84 GHz and the secondary modes generated from three-magnon splitting (labeled “1”, “2”, and “3”) under a static in-plane field of 14 mT at input powers of (a) 6 dBm and (b) 10 dBm. (c) Temporal evolution at an excitation frequency of 2.92 GHz and an input power of 10 dBm, showing a similar sequential population behavior.
• Figure 5: Simulated time-dependent intensities of the pump and secondary modes obtained from the nonlinear three-magnon model. (a) low power excitation, where only the first and second pairs are generated. (b) high power excitation, where three mode pairs appear sequentially around $f/2$. The model reproduces the delayed onset and power-dependent activation of successive magnon pairs observed experimentally.