Linear and nonlinear magnetization dynamics in permalloy thin films grown on DNA origami and nanopatterned permalloy/YIG hybrid structures

Spin waves (SWs) are collective excitations of the spin ensemble in systems with magnetic order. In quantum mechanics, a SW is known as a magnon, which is the quasiparticle describing the quantized nature of these wave-like excitations. Magnonics is the research branch in magnetism that studies magnon excitation, propagation and detection in micro- and nanostructures with the ultimate goal to control and engineer magnons for future applications in telecommunication and information processing. Indeed magnons exist in the GHz-THz range possessing wavelengths that can be as small as few nm. This frequency regime is that assigned to telecommunication. By a propagating magnon, angular momentum flows without electrical charge motion. Hence magnons can propagate through insulating oxides with magnetic order as well. The absence of Joule heating and the short wavelength have raised significant technological interest in engineering magnon-based devices to process and store information as candidate solutions to the conventional-nanoelectronics conundrum of achieving simultaneously device miniaturization, power efficiency and high operational speed. The dynamic magnetic field of a microwave antenna (CPW) irradiated by an electromagnetic wave (EMW) excites magnons in an adjacent magnetic layer. The wavelength mismatch of EMW and magnons at the same frequency limits the coupling efficiency. However to enhance coupling to magnons with a wavelength < 100 nm periodic arrays of nanomagnets are integrated at the interface between the CPW and the magnetic layer. The periodic nanomagnets act as grating coupler (GC) improving the microwave-to-magnon transduction. To optimize the GC functionality unprecedented downscaling of nanomagnet arrangements below 100 nm is sought. Such lateral length scale is hard to achieve with routinely available tools for top-down nanofabrication. In our work we fabricate ferromagnetic grating couplers on low damping YIG (Y3Fe5O12) thin films with 11 and 113 nm thickness. We study microwave-to-magnon transduction in the linear and non-linear regime up to few tens of GHz. Beyond chiral magnon properties in 11-nm-thick YIG we explore the magnon-induced reversal of Ni80Fe20 nanomagnets integrated on top of YIG. Our study as a function of YIG thickness characterizes the power efficiency of magnetization switching by different magnon resonances in hybrid structures for which we realized different interfacial coupling. We found that magnon pulses propagating in both directions induce magnetization reversal. The asymmetric group velocities for chiral magnons in the 11-nm-thick YIG are studied for wavelengths down to 99 nm. Stimulated by the efficient magnon excitation via grating couplers in top-down nanopatterned hybrid structures we then explore a novel route to create periodically modulated nanomagnets. We investigate DNA-based nanopatterning for feature sizes below 50 nm. In surface-corrugated ferromagnetic thin films we observe a frequency shift of the magnon band minimum, modified resonance frequencies of confined magnon modes and, by performing micromagnetic simulations, predict the formation of nanoengineered band structures assuming a lateral modulation on the 30-nm length scale. Our results foster the development of novel miniaturized magnetic grating couplers and stimulate future device design and optimization to achieve low-power in-memory computing via short-waved magnons and the magnon-induced reversal effect.