Structure, magnetism, and colossal magnetoresistance (CMR) of the ternary transition metal solid solution Ca_14-xEu_xMnSb₁₁ (0 < x < 14)

The solid solution of the ternary transition metal Zintl phase Ca_14-xEu_xMnSb₁₁ (0 < x < 14) has been prepared by heating a mixture of stoichiometric amounts of the elements in a two-zone furnace with T_high = 1100°C and T_low = 1050°C. The ternary transition metal compounds crystallize in the tetragonal space group I4₁/acd and are isostructural with the Zintl compound Ca₁₄AlSb₁₁. The lattice parameters of the Ca_14-xEu_xMnSb₁₁ compounds linearly increase with increasing Eu substitution for Ca. The Eu atoms preferentially occupy the Ca(2) site first and subsequently occupy Ca(4), Ca(1), and Ca(3), in order, among the four crystallographically inequivalent Ca sites. Temperature-dependent magnetic susceptibility measurements of the solid solution reveal that Eu replacement for Ca induces complex magnetic interactions in the compound, from simple ferromagnetic interactions for Ca₁₄MnSb₁₁ to ferrimagnetic interactions for Eu₁₄MnSb₁₁, because of the Eu²⁺(4f⁷) magnetic moment. The paramagnetic Curie temperature of the Ca_14-xEu_xMnSb₁₁ compounds shows an interesting change with varying x, and the magnetic easy axis gradually changes in the solid solution from perpendicular (for Ca₁₄MnSb₁₁) to parallel (for Eu₁₄MnSb₁₁) to the crystal c axis. The electrical transport properties of the Ca_14-xEu_xMnSb₁₁ (x = 0, 3, 11) compounds show a close relation to their magnetic properties and are compared to the previous results for Ca_14-xEu_xMnSb₁₁ (x = 13, 14). The influence of Eu doping on the structural and physical property of Ca_14-xEu_xMnSb₁₁ is discussed in terms of the site preferences of Eu for the four different Ca sites.