  Magnetic Weyl semimetals (WSMs) bearing long-time pursuing are still very
rare. We herein identified magnetic exchange induced Weyl state in EuCd2Sb2, a
semimetal in type IV magnetic space group, via performing high magnetic field
(B) magneto-transport measurements and ab initio calculations. For the A-type
antiferromagnetic (AFM) structure of EuCd2Sb2, external B larger than 3.2 T can
align Eu spins to be fully polarized along the c-axis and consequently drive
the system into a ferromagnetic (FM) state. Measurements up to B ~ 55 T
revealed a striking Shubnikov-de Hass oscillation imposed by a nontrivial Berry
phase. We unveiled a phase transition from a small-gap AFM topological
insulator into a FM WSM in which Weyl points emerged along the {\Gamma}-Z path.
Fermi arcs on (100) and (010) surfaces are also revealed. The results pave a
way towards realization of various topological states in a single material
through magnetic exchange manipulation.
