  Spin waves are excitations in ferromagnetic media that have been proposed as
information carriers in hybrid spintronic devices with much lower operation
power than conventional charge-based electronics. Their wave nature can be
exploited in majority gates by using interference for computation. However, a
scalable spin-wave majority gate that can be co-integrated alongside
conventional electronics is still lacking. Here, we demonstrate a sub-micron
inline spin-wave majority gate with fan-out. Time-resolved imaging of the
magnetization dynamics by scanning transmission x-ray microscopy illustrates
the device operation. All-electrical spin-wave spectroscopy further
demonstrates majority gates with sub-micron dimensions, reconfigurable input
and output ports, and frequency-division multiplexing. Challenges for hybrid
spintronic computing systems based on spin-wave majority gates are discussed.
