  Extending nanostructures into the third dimension has become a major research
avenue in modern magnetism, superconductivity and spintronics, because of
geometry-, curvature- and topology-induced phenomena. Here, we introduce Co-Fe
nanovolcanoes-nanodisks overlaid by nanorings-as purpose-engineered 3D
architectures for nanomagnonics, fabricated by focused electron beam induced
deposition. We use both perpendicular spin-wave resonance measurements and
micromagnetic simulations to demonstrate that the rings encircling the volcano
craters harbor the highest-frequency eigenmodes, while the lower-frequency
eigenmodes are concentrated within the volcano crater, due to the
non-uniformity of the internal magnetic field. By varying the crater diameter,
we demonstrate the deliberate tuning of higher-frequency eigenmodes without
affecting the lowest-frequency mode. Thereby, the extension of 2D nanodisks
into the third dimension allows one to engineer their lowest eigenfrequency by
using 3D nanovolcanoes with 30% smaller footprints. The presented nanovolcanoes
can be viewed as multi-mode microwave resonators and 3D building blocks for
nanomagnonics.
