  We report the magnetic properties of
Mg$_{0.2}$Co$_{0.2}$Ni$_{0.2}$Cu$_{0.2}$Zn$_{0.2}$O, a high-entropy oxide with
rocksalt structure, and the influence of substitutions on these properties.
From the magnetic susceptibility and neutron diffraction measurements, we found
that this compound exhibits long-range magnetic order below 120 K despite the
substantial structuraldisorder. The other rocksalt-type high-entropy oxides
with various chemical substitutions were found to host either an
antiferromagnetic order or spin-glass state depending on the amount of magnetic
ions. The presence of magnetic order for such a disordered material potentially
provide a route to explore novel magnetic properties and functions.

Strongly Correlated Electrons