Magnetism and colossal magnetoresistance of the pseudo-ternary rare-earth transition-metal compounds, Eu_14-xCa_xMnSb₁₁ (x < 3)

The compounds, Eu_14-xCa_xMnSb₁₁ (x < 3), have been prepared by heating the mixture of stoichiometric amounts of the elements, sealed in a quartz-jacketed Ta tube, in a two-zone furnace with T_high = 1100 and T_low = 1050 °C for 10 days. These compounds are isostructural with the Zintl compound Ca₁₄AlSb_11. The rare-earth transition-metal compounds crystallize in the tetragonal space group I4₁/acd, Z = 8, T = 90 K, a = 17.2235(7) and c = 22.6555(9) Å, V = 6720.7(5) ų, and R₁/wR₂ (0.0413/0.1129) for x = 1.45 and a = 17.1737(7) and c = 22.5741(10) Å, V = 6657.9(5) ų, and R₁/wR₂ (0.0392/0.1122) for x = 2.83. Temperature-dependent magnetic susceptibility measurement of the powder samples reveals complex magnetic interactions in the compounds and indicates a canted ferromagnetic configuration for Eu_14-xCa_xMnSb₁₁. As the amount of nonmagnetic Ca increases to x = 2, the effective magnetic moment decreases from 29.9 to 27.9 μB/fu., and the paramagnetic Curie temperature of the compound increases from 82.4 to 86.4 K at 1000 Oe. The magnetotransport properties of one compound, Eu₁₃CaMnSb₁₁ (x = 1), were measured and show a close relation to its magnetic properties, especially in the low-temperature region. The influence of chemical substitution on the structural and physical properties of Eu_14-xCa_xMnSb₁₁ will be discussed in terms of the site preferences of Ca doping into the four different Eu sites.