NONRECIPROCAL MAGNON PROPAGATION IN YTTRIUM IRON GARNET NANOSTRIPES WITH ASYMMETRIC DZYALOSHINSKII–MORIYA INTERACTION GRADIENTS: VOLTAGE-CONTROLLED SPIN-WAVE DIODE FUNCTIONALITY AT 300 K

Abstract

We report the design, fabrication and experimental realization of voltage controlled Dzyaloshinskii–Moriya interaction (DMI) gradients in yttrium iron garnet (YIG) nanostripes, showing voltage-controlled nonreciprocal propagation of magnons at room temperature (300 K). Gadolinium gallium garnet (GGG) substrates were used for growing nanostripes with pulsed laser deposition technique and patterning by electron-beam lithography, using a thickness of 20nm and widths of 400nm. An asymmetric deposition of the Pt/W interfacial bilayer (0.5–3.0 nm) was performed along the nanostripe axis in order to create a spatially varying DMI constant D(x). The modulation was realized by a gate electrode comprising of an HfO₂ (10 nm) dielectric and Au top electrode. The direction-dependent spin-wave group velocities, up to 18% different, are confirmed by Brillouin light scattering (BLS) spectroscopy and vector network analyzer (VNA) spin-wave spectroscopy, with a maximum nonreciprocal isolation ratio (η) = 14.3 dB at 6.4 GHz. The experimental dispersion asymmetry is reproduced by micromagnetic simulations with MuMax3 using spatially varying D(x), with an accuracy of 5% over a range of −4 to +4 V gate voltage.The experimental dispersion asymmetry is reproduced by micromagnetic simulations with MuMax3 using spatially varying D(x) with accuracy of 5% within the gate voltage range of −4 to +4 V. An asymmetric oxygen vacancy gradient at the YIG/Pt interface is confirmed by X-ray photoelectron spectroscopy (XPS) and electron energy-loss spectroscopy (EELS) as the primary chemical source of the DMI gradient. The Gilbert damping constant α of the nanostripes is α = 2.1 × 10⁻³, which indicates low loss magnon transport remains. These findings lay a foundation for the realization of a chemically designed, oxide compatible, low-power spin-wave diode operating at 300 K and open the way towards voltage-reconfigurable magnonic logic circuits.