Origin of colossal magnetoresistance in EuZn₂P₂

EuZn₂P₂ is part of a trigonal family (CaAl₂Si₂-type structure) of Eu-based layered compounds that has recently seen increased interest due to their potential topological properties and other exciting phenomena that result from intertwined electronic, magnetic, and lattice degrees of freedom. EuZn₂P₂ has been previously shown to be a narrow-gap insulator with canted A-type antiferromagnetic order (T_N = 23 K) and large negative colossal magnetoresistance (CMR) well above and below the Néel temperature, as well as strongly enhanced magnetism and semi-metallic conductivity under pressure. The origin of the colossal magnetoresistance effect in this material and other Eu²⁺ compounds is still poorly understood but has been previously attributed to magnetic fluctuations, the formation of magnetic polarons, or electronic band reconstruction. Here, we propose that the formation of magnetic polarons in the paramagnetic state are responsible for the CMR response. We report comprehensive electrical transport, magnetization, thermal expansion and electron spin resonance measurements on indium flux grown samples that are consistent with magnetic polaron formation in the paramagnetic state. Finally, we discuss the potential origin of negative magnetoresistance observed within the ordered state.