  Bulk CsEuBr$_3$ and CsEuCl$_3$ are experimentally shown to be magnetic
semiconductors that order antiferromagnetically at Neel temperatures of 2.0 K
and 1.0 K respectively. Given that nanoparticles and thin films of CsEuCl$_3$
have been reported to order ferromagnetically at a similar temperature, our
observation of antiferromagnetic ordering in CsEuBr$_3$ and CsEuCl$_3$ expands
the possible applications of halide perovskites to now include spintronic
devices where both ferromagnetic and antiferromagnetic devices can be
fabricated from a single material. The conclusion that CsEuCl$_3$ can be used
as a switchable magnetic material is also supported by our density-functional
theory calculations.
