  Dirac materials exhibit intriguing low-energy carrier dynamics that offer a
fertile ground for novel physics discovery. Of particular interest is the
interplay of Dirac carriers with other quantum phenomena, such as magnetism.
Here we report on a two-magnon Raman scattering study of AMnBi2 (A=Ca, Sr), a
prototypical magnetic Dirac system comprising alternating Dirac-carrier and
magnetic layers. We present the first accurate determination of the exchange
energies in these compounds and, by comparison to the reference compound
BaMn2Bi2, we show that the Dirac-carrier layers in AMnBi2 significantly enhance
the exchange coupling between the magnetic layers, which in turn drives a
charge-gap opening along the Dirac locus. Our findings break new grounds in
unveiling the fundamental physics of magnetic Dirac materials, which offer a
novel platform for probing a distinct type of spin-Fermion interaction. The
outstanding properties of these materials allow a delicate manipulation of the
interaction between the Dirac carriers and magnetic moments, thus holding great
promise for applications in magnetic Dirac devices.
