Structure, Magnetism, and Magnetoresistance of the Compounds Eu₁₄MnAs₁₁ and Eu₁₄MnP₁₁

The new compounds Eu 14 MnAs 11 and Eu 14 MnP 11 were synthesized from stoichiometric amounts of the elements. The compounds are isotypic to Ca 14 AlSb 11 and crystallize in the tetragonal space group I 4 1 / acd ( Z = 8). Lattice parameters obtained from single-crystal X-ray diffraction at 130 K are a = 16.318 (2) Å, c = 21.684 (4) Å and a = 15.930 (4) Å, c = 21.213 (5) Å for Eu 14 MnAs 11 and Eu 14 MnP 11, respectively. In the refinement of each structure, the central Pn(4) site of a Pn 3 7 - linear unit (Pn = As, P) shows positional disorder; this is in contrast to the ordered structures formed when Pn = Sb and Bi. Eu 14 MnAs 11 and Eu 14 MnP 11 are ferromagnetic with transitions at 74 and 52 K, respectively. Eu 14 MnAs 11 also has a low-temperature transition at ∼25 K. Resistivity measurements indicate an insulator-to-metal transition near the magnetic transition, and plots of ln ρ vs 1/ T are linear above T C, providing activation energies of 0.03 eV (As; 240−300 K) and 0.31 eV (P). The resistivity is suppressed in the presence of a magnetic field, with the greatest dρ occurring at a magnetic transition similar to that found in other colossal magnetoresistive materials. The magnetoresistivity (MR) ratios (ρ( H =0) − ρ( H =5T))/ρ( H =5T) at the magnetic transition are 1200 at 55 K (Eu 14 MnP 11 ) and 2 at 74 K (Eu 14 MnAs 11 ). Structural features as well as magnetic, electronic, and magnetotransport properties are presented and compared within the Eu 14 MnPn 11 series.