  We experimentally investigate spin-polarized transport between a
ferromagnetic Ni electrode and a surface of Weyl semimetal, realized in a thick
WTe$_2$ single crystal. For highly-transparent Ni-WTe$_2$ planar junctions, we
observe non-Ohmic $dV/dI(I)$ behavior with an overall increase of differential
resistance $dV/dI$ with current bias, which is accomplished by current-induced
switchings. This behavior is inconsistent with trivial interface scattering,
but it is well known for spin-polarized transport with magnon emission. Thus,
we interpret the experimental results in terms of spin wave excitation in spin
textures in the WTe$_2$ topological surface states, which is supported by the
obtained magnetic field and temperature $dV/dI(I)$ dependencies.
