  Weyl fermions have recently been observed in several time-reversal-invariant
semimetals and photonics materials with broken inversion symmetry. These
systems are expected to have exotic transport properties such as the chiral
anomaly. However, most discovered Weyl materials possess a substantial number
of Weyl nodes close to the Fermi level that give rise to complicated transport
properties. Here we predict, for the first time, a new family of Weyl systems
defined by broken time-reversal symmetry, namely, Co-based magnetic Heusler
materials XCo2Z (X = IVB or VB; Z = IVA or IIIA). To search for Weyl fermions
in the centrosymmetric magnetic systems, we recall an easy and practical
inversion invariant, which has been calculated to be -1, guaranteeing the
existence of an odd number of pairs of Weyl fermions. These materials exhibit,
when alloyed, only two Weyl nodes at the Fermi level - the minimum number
possible in a condensed matter system. The Weyl nodes are protected by the
rotational symmetry along the magnetic axis and separated by a large distance
(of order 2$\pi$) in the Brillouin zone. The corresponding Fermi arcs have been
calculated as well. This discovery provides a realistic and promising platform
for manipulating and studying the magnetic Weyl physics in experiments.
