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 I4(1)/acd (Z = 8). Lattice parameters obtained from single-crystal X-ray diffraction at 130 Ii are alpha = 16.318 (2) Angstrom, c = 21.684 (4) Angstrom and alpha = 15.930 (4) Angstrom, c = 21.213 (5) Angstrom for Eu14MnAs11 and Eu14MnP11, 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 = Sta and Bi, Eu14MnAs11 and Eu14- MnP11 are ferromagnetic with transitions at 74 and 52 K, respectively. Eu14MnAs11 also has a low-temperature transition at similar to 25 K. Resistivity measurements indicate an insulator-to-metal transition near the magnetic transition, and plots of ln rho vs 1/T are linear above To, providing activation energies of 0.03 eV (As; 248-300 Kj and 0.31 eV (P). The resistivity is suppressed in the presence of a magnetic field, with the greatest dp occurring at a magnetic transition similar to that found in other colossal magnetoresistive materials. The magnetoresistivity (MR) ratios (rho (H=0) - rho (H=5T))/rho (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 Eu(14)MnPn(11) series.