  In contrast to the cuprates, where the proximity of antiferromagnetism (AFM)
and superconductivity is well established, first indications for AFM
interactions in superconducting infinite-layer nickelates were only recently
obtained. Here, we explore, based on first-principles simulations, the nature
of the magnetic coupling in NdNiO2 as a function of the on-site Coulomb and
exchange interaction, varying the explicit hole doping and the treatment of the
Nd $4f$ electrons. The $U$-$J$ phase diagrams for undoped nickelates and
cuprates indicate $G$-type ordering, yet show different $U$ dependency. By
either Sr hole doping or explicit treatment of the Nd $4f$ electrons, we find a
transition to a Ni $C$-type AFM ground state. We trace the effect of Sr doping
back to a distinct accommodation of the holes by the Ni versus Cu $e_g$
orbitals. The interaction between Nd $4f$ and Ni $3d$ states stabilizes
$C$-type AFM order on both sublattices. Though spin-orbit interactions induce a
band splitting near the Fermi energy, the bad-metal state is retained even
under epitaxial strain. These results establish the distinct role of the
magnetic interactions in the nickelates versus the cuprates and suggest the
former as a unique platform to investigate the relation to unconventional
superconductivity.
