Extending nanostructures into the third dimension has become a major research avenue in modern magnetism and spintronics because of geometry-, curvature-, and topology-induced phenomena. Here, we introduce nanovolcanoes as on-demand engineered nano-architectures for 3D magnon spintronics. 40 nm-thick Co-Fe nanovolcanoes with diameters down to 300 nm were fabricated by the focused electron beam-induced deposition (FEBID) technique (Fig. 1) and studied by perpendicular spin-wave resonance (PSWR) spectroscopy. The spin-wave eigenfrequencies of the nanovolcanoes are notably different from the eigenfrequencies of the nanodisks and nanorings they are built from, because of the strongly non-uniform internal magnetic field. The experimental findings were elucidated with the aid of micromagnetic simulations, which indicate that the rings encircling the volcano craters lead to an effective confinement of the lower-frequency eigenmodes under the volcano crater, while the highest-frequency eigenmodes are confined in the ring area (Fig. 2). Accordingly, extension of 2D nanodisks into 3D nanovolcanoes allows to obtain same response in low frequency part of the spectrum in elements with 30% smaller footprints [1]. The nanovolcanoes can be viewed as multi-mode resonators with potential applications in telecom industry. Also, we demonstrated the engineering of the magnetic properties of CoFe-based nanodisks fabricated by FEBID. The material composition was tuned in situ via the e-beam waiting time in the deposition process and their post-growth irradiation with Ga ions. The saturation magnetization Ms of the nanodisks was deduced from PSWR measurements. The achieved variation of Ms in the broad range from 720 to 1430 emu/cm3 continuously bridges the gap between the Ms values of widely used magnonic materials such as Permalloy and CoFeB [2].

![](https://assets.underline.io/uploads/markdown_image/1/image/ca3695146d0c42bbf0d0b907eb2d1eb1.jpg)

Fig. 1. Atomic force microscopy image of the nanovolcano with the outer diameter of 300 nm and the crater diameter of 200 nm. Inset: cross-sectional line scan.

![](https://assets.underline.io/uploads/markdown_image/1/image/355d13301bed6b9caa1885c2c3af1f2e.jpg)

Fig. 2. Calculated spatial dependences of the spin-wave eigenfunctions for (a) 40 nm-thick nanovolcano NV300/200, (b) 20 nm-thick nanodisk ND300, and (c) 20 nm-thick nanoring NR300/200 at the out-of-plane bias magnetic field of 1.2 T.

Spin-wave spectra of 3D nanovolcanoes fabricated by focused electron beam-induced deposition

**Session chair:** Oleksii Volkov, Helmholtz-Zentrum Dresden-Rossendorf



HOL - Spin Waves and Magnetization Dynamics II

technical paper

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This Conference provides an outstanding opportunity for worldwide participants to meet their colleagues and collaborators and discuss developments in all areas of magnetism research.

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Spin-wave spectra of 3D nanovolcanoes fabricated by focused electron beam-induced deposition

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