A-type antiferromagnetic order and magnetic phase diagram of the trigonal Eu spin-7/2 triangular-lattice compound EuSn2As2

TL;DR

This study investigates the magnetic order and phase diagram of EuSn2As2, revealing a collinear A-type antiferromagnetic structure below 24 K and exploring its magnetic response to temperature and magnetic field.

Contribution

The paper provides detailed neutron-diffraction and magnetic measurements establishing the magnetic ground state and phase diagram of EuSn2As2, a compound with Dirac surface states and antiferromagnetic order.

Findings

EuSn2As2 exhibits A-type antiferromagnetic order below 24 K.

Magnetic phase diagrams are constructed for different field orientations.

The compound shows dynamic spin fluctuations up to 60 K.

Abstract

The trigonal compound EuSn2As2 was recently discovered to host Dirac surface states within the bulk band gap and orders antiferromagnetically below the Neel 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 single-crystal neutron-diffraction measurements versus T, magnetization M(H,T), magnetic susceptibility chi(H,T) = M(T)/H, heat capacity Cp(H,T), and electrical resistivity rho(H,T) measurements. The neutron-diffraction and chi(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 chi(H{ab},T) and chi(H{c},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 chi(T), Cp(T) and rho(H,T) measurements, a temperature that is more than twice TN. The rho(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), chi(H,T), Cp(H,T), and rho(H,T) data.