  The $\gamma$-ray strength function, or average reduced $\gamma$-ray
transition probability, is a fundamental input in the calculation of
$(n,\gamma)$ cross sections used to simulate the nucleosynthesis of elements
heavier than Fe. Since 2004, an enhanced probability of $\gamma$-decay with
$\gamma$-ray energies below $\approx2 - 4$ MeV has been measured in reaction
data for numerous nuclei. This has been observed as an increase in the
$\gamma$-ray strength with decreasing $\gamma$-ray energy, often referred to as
the low-energy enhancement or \textit{upbend} in the $\gamma$-ray strength.
Nevertheless, the available data confirming this enhancement corresponded
solely to charged-particle included reactions and no low-energy enhancement had
yet been confirmed from neutron-induced reaction measurements. In this work, we
present the first evidence of low-energy $\gamma$-ray strength enhancement from
neutron-capture reaction data. Gamma-ray spectra following thermal neutron
capture on $^{58,60}$Ni have been used to determine the strength for primary
and secondary $\gamma$-rays in $^{59,61}$Ni, showing an enhancement for
$\gamma$-ray energies below $\approx 3$ MeV and $\approx 2$ MeV for
$^{59,61}$Ni, respectively. For the first time, this enhancement is observed
down to $\gamma$-ray energies of $\approx0.2$ MeV. Further, available
spin-parity assignments have been used to obtain the multipolarity and
electromagnetic character of these transitions, showing that this low-energy
enhancement is dominated by $M1$ and $E2$ strength, with $E1$ strength also
exceeding Standard Lorentzian Model predictions. Finally, large-basis
shell-model calculations have been performed, also predicting a strong $M1$
enhancement at low $\gamma$-ray energies.
