  Analogues of the elementary particles, Dirac fermions in condensed matter
have received extensive attention for both scientific interest and device
applications. In this work, we generalize the concept of Dirac semimetal (DSM)
to the magnetic space groups (MSGs), and define a new category of DSM in type
IV MSGs, which is protected by the antiunitarity of the product of the
inversion symmetry and the nonsymmophic time-reversal symmetry. Moreover, we
propose the interlayer antiferromagnetic (AFM) EuCd2As2 as a promising
candidate with only one pair of Dirac points at the Fermi level. Many exotic
topological states, such as the triple point semimetal and the AFM topological
insulator holding of the half-quantum Hall effect, can be derived from such AFM
DSMs by breaking certain symmetry, providing an ideal platform to study
topological phase transitions. Our results extend the range of DSM, and open a
new way to study the interplay between the DSM and other exotic topological
states.
