Nuclear and magnetic structures of ND 4MnFeF 6 at 4.2 K

Abstract

The nuclear and magnetic structures of the antiferromagnet ( T N = 117.7 ± 0.5 K) ND 4MnFeF 6 are studied by neutron powder diffraction at 4.2. K. The orthorhombic structure ( a = 10.5276(4) A ̊ , b = 7.7970(2) A ̊ , c = 12.8156(4) A ̊ , Pnc2 , Z = 4) is built from edge-sharing MnFeF 10 bioctahedra in which a Mn 2+Fe 3+ cationic ordering occurs. The position of the ND + 4 groups is not clearly established. Using the centric space-group Pbcn, the N(1)D + 4 group is “hydrogen” bonded to the flouirine skeleton, while the N(2)D + 4 unit occupies statistically two two-fold axis related positions. Both ND + 4 tetrahedra are almost regular ( 〈N−D〉 = 0.996 A ̊ ). With the non-centric space-group, every ND + 4 unit is “hydrogen” bonded but interatomic distances suffer slight deviations from mean-current values. Below T N , the nuclear and magnetic cells are identical; the choice of the space group, Pbcn or Pnc2, does not affect the results concerning the magnetic structure. The spins of Mc 2+ and Fe 3+ ( μ = 4.42(5) μB) are perpendicular to the mean plane of the bioctahedra and all the d5- d5 type superexchange interactions either of the 90 or of 180° type are antiferromagnetic.