Magnetoresistance and Anisotropic Spin Dynamics in Antiferromagnetic Semiconductor Eu_5Sn_2As_6

We report on the thermodynamic and transport properties of the rare-earth Zintl compound Eu_5Sn_2As_6, which orders as a canted antiferromagnetic magnetic 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, Eu_5Sn_2As_6 exhibits negative colossal magnetoresistance of up to a factor of 6×10^3. This may be 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.