Coupling of magnetic order and charge transport in the candidate Dirac semimetal EuCd2As2

We use resonant elastic x-ray scattering to determine the evolution of magnetic order in EuCd2As2 below T-N = 9.5K, as a function of temperature and appliedmagnetic field. We find an A-type antiferromagnetic structure with in-plane magnetic moments, and observe dramatic magnetoresistive effects associated with field-induced changes in the magnetic structure and domain populations. Our ab initio electronic structure calculations indicate that the Dirac dispersion found in the nonmagnetic Dirac semimetal Cd3As2 is also present in EuCd2As2, but is gapped forT < T-N due to the breaking of C-3 symmetry by the magnetic structure.