LAUSR

The trigonal compound EuSn2As2 was recently discovered to host Dirac surface states within the bulk band gap and orders antiferromagnetically below the Néel temperature TN ≈ 24 K. Here the magnetic ground state of single-crystal EuSn2As2 and the evolution of its properties versus temperature T and applied magnetic field H are reported. Included are zero-field singlecrystal neutron diffraction measurements versus T , magnetization M(H,T ), magnetic susceptibility χ(H,T ) = M(H,T )/H, heat capacity Cp(H,T ), and electrical resistivity ρ(H,T ) measurements. The neutron-diffraction and χ(T ) measurements both indicate a collinear A-type antiferromagnetic (AFM) structure below TN = 23.5(2) K, where the Eu 2+ spins S = 7/2 in a triangular ab-plane layer (hexagonal unit cell) are aligned ferromagnetically in the ab plane whereas the spins in adjacent Eu planes along the c axis are aligned antiferromagnetically. The χ(Hab, T ) and χ(Hc, T ) data together indicate a smooth crossover between the collinear AFM alignment and an unknown magnetic structure at H ∼ 0.15 T. Dynamic spin fluctuations up to 60 K are evident in the χ(T ), Cp(T ) and ρ(H,T ) measurements, a temperature that is more than twice TN. The ρ(H,T ) of the compound does not reflect a contribution of the topological state, but rather is consistent with a low-carrier-density metal with strong magnetic scattering. The magnetic phase diagrams for both H ‖ c and H ‖ ab in the H-T plane are constructed from the TN(H), χ(H,T ), Cp(H,T ), and ρ(H,T ) data.