  A measurement of the top-quark mass ($m_t$) in the
$t\bar{t}\rightarrow~\textrm{lepton}+\textrm{jets}$ channel is presented, with
an experimental technique which exploits semileptonic decays of $b$-hadrons
produced in the top-quark decay chain. The distribution of the invariant mass
$m_{\ell\mu}$ of the lepton, $\ell$ (with $\ell=e,\mu$), from the $W$-boson
decay and the muon, $\mu$, originating from the $b$-hadron decay is
reconstructed, and a binned-template profile likelihood fit is performed to
extract $m_t$. The measurement is based on data corresponding to an integrated
luminosity of 36.1 fb$^{-1}$ of $\sqrt{s} = 13~\textrm{TeV}$ $pp$ collisions
provided by the Large Hadron Collider and recorded by the ATLAS detector. The
measured value of the top-quark mass is $m_{t} =
174.41\pm0.39~(\textrm{stat.})\pm0.66~(\textrm{syst.})\pm0.25~(\textrm{recoil})~\textrm{GeV}$,
where the third uncertainty arises from changing the PYTHIA8 parton shower
gluon-recoil scheme, used in top-quark decays, to a recently developed setup.
