Colossal magnetoresistance and anisotropic spin dynamics in the antiferromagnetic semiconductor Eu 5 Sn 2 As 6

We report on the thermodynamic and transport properties of the rare-earth Zintl compound ${\mathrm{Eu}}₅{\mathrm{Sn}}₂{\mathrm{As}}₆$, which orders as a canted antiferromagnetic semiconductor at 10.3 K. The system also displays a complex cascade of magnetic phases arising from geometric and magnetic exchange frustration, with high sensitivity to the application and direction of small magnetic fields. At low temperature, ${\mathrm{Eu}}₅{\mathrm{Sn}}₂{\mathrm{As}}₆$ exhibits negative colossal magnetoresistance of up to a factor of 6000. This represents a lower bound as the conductivity appears to be shunted by an unknown conduction channel, causing the resistivity to saturate. Mechanisms for the low-temperature saturation of resistivity are discussed.