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

The new compounds Eu14MnAs11 and Eu14MnP11 were synthesized from stoichiometric amounts of the elements. The compounds are isotypic to Ca14AlSb11 and crystallize in the tetragonal space group I41/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 Eu14MnAs11 and Eu14MnP11, respectively. In the refinement of each structure, the central Pn(4) site of a Pn37- linear unit (Pn = As, P) shows positional disorder; this is in contrast to the ordered structures formed when Pn = Sb and Bi. Eu14MnAs11 and Eu14MnP11 are ferromagnetic with transitions at 74 and 52 K, respectively. Eu14MnAs11 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 TC, 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 (Eu14MnP11) and 2 at 74 K (Eu14MnAs11). Structural features as well as magnetic, electronic, and magnetotransport properties are presented and compared within the Eu14MnPn11 series.