Vibrational spectra and magnetic properties of Eu-3[BN2](2) and LiEu4[BN2](3)

Abstract

Eu-3[BN2](2) and LiEu4[BN2](3) were synthesized from a stoichiometric mixture of EuN, BN, europium metal and Li3N, EuN and BN (ratio: 1:4:3) in sealed niobium ampoules at 1475 and 1275 K, respectively. Temperature dependent susceptibility measurements of Eu-3[BN2](2) and LiEu4[BN2](3) show Curie-Weiss behavior with experimental magnetic moments of 8.03(5) and 8.5(1) mu(B)/Eu atom, respectively, compatible with divalent europium. Both nitridoborates order ferromagnetically at T-C = 32.0(5) K (Eu-3[BN2](2)) and 22.0(5) K (LiEu4[BN2](3)). The saturation magnetizations of 5.73(5) mu(B)/Eu atom at 5 K and 7 T for Eu-3[BN2](2) and 4.2 mu(B)/Eu atom at 5 K and 2 T for LiEu4(BN2)(3) are smaller than the maximum value of 7 mu(B). Eu-151 Mossbauer data of Eu-3[BN2](2) at 4.2 K show an isomer shift of -11.4(1) mm/s and an experimental line width of 3.1(2) mm/s. Full magnetic hyperfine field splitting with 26.2(3) T at the europium nuclei is detected. Vibrational spectra of Eu-3[BN2](2) are interpreted on the basis of discrete [BN2](3-) units with symmetry D-infinityh by taking into account the existence of two crystallographically independent [BN2](3-) anions and their dynamic coupling in the unit cell (factor group splitting).