  Weyl semimetals exhibit exceptional quantum electronic transport due to the
presence of topologically-protected band crossings called Weyl nodes. The nodes
come in pairs with opposite chirality, but their number and location in
momentum space is otherwise material specific. Following the initial
discoveries there is now a need for better material realizations, ideally
comprising a single pair of Weyl nodes located at or very close to the Fermi
level and in an energy window free from other overlapping bands. Here we
propose the layered intermetallic EuCd$_2$As$_2$ to be such a system. We show
that Weyl nodes in EuCd$_2$As$_2$ are magnetically-induced via exchange
coupling, emerging when the Eu spins are aligned by a small external magnetic
field. The identification of EuCd$_2$As$_2$ as a model magnetic Weyl semimetal,
evidenced here by ab initio calculations, photoemission spectroscopy, quantum
oscillations and anomalous Hall transport measurements, opens the door to
fundamental tests of Weyl physics.
