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We investigate the rare earth Zintl semiconductor Eu₅Sn₂As₆, a compound in a family of materials predicted to be magnetic topological insulators [1]. We find a colossal negative magnetoresistance spanning almost four orders of magnitude and, using electrical transport, magnetization, and heat capacity measurements, reveal a rich phase diagram in temperature and field. Magnetoresistance and non-linear electrical transport measurements help unveil the role of magnetic polarons on electrical transport and on the magnetic structure. Mechanisms through which the magnetic polarons may interact are discussed as well as investigations of the predicted topological character of the material.

[1] Nicodemos Varnava, Tanya Berry, Tyrel M. McQueen, and David Vanderbilt, “Engineering magnetic topological insulators in Eu₅M₂X₆ Zintl compounds” Phys. Rev. B 105, 235128 (2022)