Synthesis, magnetic properties, and colossal magnetoresistance of Eu_13.97Gd_0.03MnSb₁₁

The synthesis, crystal structure, magnetization, and resistivity of Gd-doped Eu₁₄MnSb₁₁, Eu_13.97Gd_0.03MnSb₁₁, are reported and compared to Eu₁₄MnSb₁₁ and Eu₁₄MnBi₁₁. All three compounds are isostructural with the Zintl compound Ca₁₄AlSb₁₁. The Gd-doped Eu transition metal Zintl compound crystallizes in the tetragonal space group I4₁/acd with a=17.338(3) Å and c=22.691(5) Å, where Gd partially replaces Eu in the structure. The compound displays three magnetic phase transitions: a ferromagnetic transition near 80 K, an apparent antiferromagnetic transition at a field-dependent T_N (T_N=30 K in zero field), and a spin-reorientation transition with a transition temperature that is near 15 K in zero field but is also field dependent. Measurements of both zero-field resistivity for 5≤T≤300 K and the magnetoresistance in fields up to 5 T for the same temperatures are presented. Negative magnetoresistance is observed over a wide range of temperatures below 200 K.