Colossal negative magnetoresistance in an antiferromagnet

The magnetization and resistivity of single crystals of the Zintl compound Eu₁₄MnBi₁₁ are measured as functions of temperature and applied magnetic field. The magnetization data show an apparent antiferromagnetic transition at TN=32K even though the high-temperature susceptibility suggests that the exchange coupling is ferromagnetic in nature. The zero-field resistivity is approximately independent of temperature above 32 K. Below 32 K the resistivity increases slightly and peaks at about 20 K before decreasing as the temperature is decreased. This temperature dependence is fairly normal for an antiferromagnetic metal. On the other hand, in contrast to other antiferromagnets, the single-crystal magnetoresistance is large and negative at all temperatures below about 3TN. In addition, the dependence of the resistivity upon the magnetization is quite similar to the colossal-magnetoresistance materials.