  Spin transport through magnetic insulators via magnons has recently been
explored for a growing variety of magnetic systems with long-range order and
well-understood spin excitation spectra. Here we show dramatic effects of spin
transport through an amorphous magnetic insulator, which is both magnetically
and structurally disordered. We generate and detect spin flow though amorphous
yttrium-iron-garnet ($a$-YIG) thin films in a non-local geometry by use of the
spin Hall and inverse spin Hall effects in platinum strips separated by 10 or
more microns. By comparing non-local spin transport in $a$-YIG on suspended
micromachined thermal isolation platforms to the same experiment performed on a
bulk substrate, we show strong effects of in-plane thermal gradients on spin
transport in the disordered magnetic insulator. The resulting non-local voltage
signals are orders of magnitude larger than those seen in crystalline magnetic
insulators, with easily measurable spin signals seen even at distances in
excess of $100$ microns. In analogy to heat transport, where disordered
materials support a range of vibrational excitations that can allow large
thermal conductivities, we suggest that efficient spin transport in disordered
magnetic systems can occur via a similar spectrum of excitations that relies on
strong local exchange interactions and does not require long-range order. This
work not only opens a new area for fundamental experimental and theoretical
studies of spin transport, but also sets a new direction in materials science
for magnonic and spintronic devices.
