  We measure the cross-correlation between redMaGiC galaxies selected from the
Dark Energy Survey (DES) Year-1 data and gravitational lensing of the cosmic
microwave background (CMB) reconstructed from South Pole Telescope (SPT) and
Planck data over 1289 sq. deg. When combining measurements across multiple
galaxy redshift bins spanning the redshift range of $0.15<z<0.90$, we reject
the hypothesis of no correlation at 19.9$\sigma$ significance. When removing
small-scale data points where thermal Sunyaev-Zel'dovich signal and nonlinear
galaxy bias could potentially bias our results, the detection significance is
reduced to 9.9$\sigma$. We perform a joint analysis of galaxy-CMB lensing
cross-correlations and galaxy clustering to constrain cosmology, finding
$\Omega_{\rm m} = 0.276^{+0.029}_{-0.030}$ and
$S_{8}=\sigma_{8}\sqrt{\mathstrut \Omega_{\rm m}/0.3} =
0.800^{+0.090}_{-0.094}$. We also perform two alternate analyses aimed at
constraining only the growth rate of cosmic structure as a function of
redshift, finding consistency with predictions from the concordance
$\Lambda$CDM model. The measurements presented here are part of a joint
cosmological analysis that combines galaxy clustering, galaxy lensing and CMB
lensing using data from DES, SPT and Planck.
