Vibrational spectra and magnetic properties of Eu3[BN2]2 and LiEu4[BN2]3

Abstract

Eu3[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 Eu3[BN2]2 and LiEu4[BN2]3 show Curie-Weiss behavior with experimental magnetic moments of 8.03(5) and 8.5(1) μB/Eu atom, respectively, compatible with divalent europium. Both nitridoborates order ferromagnetically at TC = 32.0(5) K (Eu3[BN2]2) and 22.0(5) K (LiEu4[BN2]3). The saturation magnetizations of 5.73(5) μB/Eu atom at 5 K and 7 T for Eu3[BN2]2 and 4.2 μB/Eu atom at 5 K and 2 T for LiEu4(BN2)3 are smaller than the maximum value of 7 μB. 151Eu Mössbauer data of Eu3[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 Eu3[BN2]2 are interpreted on the basis of discrete [BN2]3— units with symmetry D∞h by taking into account the existence of two crystallographically independent [BN2]3— anions and their dynamic coupling in the unit cell (factor group splitting).