Hyperfine interactions in the 13 K ferromagnet Eu2Si5N8

Single-phase Eu2Si5N8 was synthesized from metallic europium and silicon diimide in a tungsten crucible using a big h frequency furnace. The Eu2Si5N8 structure consists of a three-dimensional network of corner sharing SiN4 tetrahedra in which the europium ions occupy two crystallographically different sites. Magnetic susceptibility measurements of Eu2Si5N8 show Curie-Weiss behaviour above 50 K with an experimental magnetic moment of 7.67(5)mu(B)/Eu, indicating divalent europium. Ferromagnetic ordering is detected at 13.0(5) K. The saturation magnetic moment is 7.0(1)mu(B)/Eu at 5 T and 4.5 K. The two europium sites could not be distinguished by Eu-151 Mossbauer spectroscopy. The room temperature spectrum could be fitted by only one signal at an isomer shift of delta = -11.82(5) mm/s subject to quadrupole splitting of DeltaE(Q) = 16.8(2) mm/s and an asymmetry parameter of 0.67(7). At 4.2 K full magnetic hyperfine field splitting is observed with a hyperfine field of 24.9(2) T at the europium nuclei. (C) 2002 Elsevier Science Ltd. All rights reserved.