Effect of Eu magnetism on the electronic properties of the candidate Dirac material EuMnBi2

The crystal structure and physical properties of the layered material EuMnBi2 have been characterized by measurements on single crystals. EuMnBi2 is isostructural with the Dirac material SrMnBi2 based on single crystal x-ray diffraction, crystallizing in the I4/mmm space group (No. 139). Magnetic susceptibility measurements suggest antiferromagnetic (AFM) ordering of moments on divalent Eu ions near T_N=22K. For low fields, the ordered Eu moments are aligned along the c-axis, and a spin-flop is observed near 5.4T at 5K. The moment is not saturated in an applied field of 13T at 5K, which is uncommon for compounds containing Eu^{2+}. The magnetic behavior suggests an anisotropy enhancement via interaction between Eu and the Mn moments that appear to be order antiferromagnetically below approximately 310K. A large increase in the magnetoresistance is observed across the spin-flop, with absolute magnetoresistance reaching approximately 650% at 5K and 12T. Hall effect measurements reveal a decrease in the carrier density below T_N, which implies a manipulation of the Fermi surface by magnetism on the sites surrounding the Bi square nets that lead to Dirac cones in this family of materials.