  Strongly-interacting nanomagnetic systems are pivotal across next-generation
technologies including reconfigurable magnonics and neuromorphic computation.
Controlling magnetisation state and local coupling between neighbouring
nanoelements allows vast reconfigurable functionality and a host of associated
functionalities. However, existing designs typically suffer from an inability
to tailor inter-element coupling post-fabrication and nanoelements restricted
to a pair of Ising-like magnetisation states. Here, we propose a new class of
reconfigurable magnonic crystal incorporating nanodisks as the functional
element. Magnetic nanodisks are crucially bistable in macrospin and vortex
states, allowing inter-element coupling to be selectively activated (macrospin)
or deactivated (vortex). Through microstate engineering, we leverage the
distinct coupling behaviours and magnonic band structures of bistable nanodisks
to achieve reprogrammable magnonic waveguiding, bending, gating and
phase-shifting across a 2D network. The potential of nanodisk-based magnonics
for wave-based computation is demonstrated via an all-magnon interferometer
exhibiting XNOR logic functionality. Local microstate control is achieved here
via topological magnetic writing using a magnetic force microscope tip.

Mesoscale and Nanoscale Physics