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 T-N = 32 K 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 3 T-N. In addition, the dependence of the resistivity upon the magnetization is quite similar to the colossal-magnetoresistance materials.