Noncollinear antiferromagnetic structure of the molecule-based magnet Mn[N(CN)2]2

Journal ArticleThe crystallographic and magnetic properties of the Mn[N(CN)2]2 compound have been investigated by dc magnetization, ac susceptibility, specific heat, and zero-field neutron diffraction on polycrystalline samples. The magnetic structure consists of two sublattices which are antiferromagnetically coupled and spontaneously canted. The spin orientation is mainly along the a axis with a small uncompensated moment along the b axis. The ground state is a crystal-field sextet with large magnetic anisotropy. The crystal structure consists of discrete octahedra which are axially elongated and successively tilted in the ab plane. Comparisons of the magnetic structures for the isostructural M[N(CN)2] 2 (M=Mn, Fe, Co, Ni) series suggest that the spin direction is stabilized by crystal fields and the spin canting is induced by the successive tilting of the octahedra. We propose that the superexchange interaction is the mechanism responsible for the magnetic ordering in these compounds and we find that a crossover from noncollinear antiferromagnetism to collinear ferromagnetism occurs for a superexchange angle of ac=142.0(5)°

Collinear ferromagnetism and spin orientation in the molecule-based magnets M[N(CN)2]2 (M=Co,Ni)

Journal ArticleZero-field unpolarized neutron powder diffraction has been used to study the low-T magnetic structure and T-dependent crystal structure of M[N(CN)2]2 (M=Co,Ni). Both compounds show collinear ferromagnetism with spin orientation along the c axis. The results provide the determination of a complete magnetic structure in the ordered state for a molecule-based magnet. The c lattice parameter exhibits negative thermal expansion, explained by a wine-rack-like deformation

Electronic Structure of Transition-Metal Dicyanamides Me[N(CN)2_2]2_2 (Me = Mn, Fe, Co, Ni, Cu)

The electronic structure of Me[N(CN)$_2$]$_2$ (Me=Mn, Fe, Co, Ni, Cu) molecular magnets has been investigated using x-ray emission spectroscopy (XES) and x-ray photoelectron spectroscopy (XPS) as well as theoretical density-functional-based methods. Both theory and experiments show that the top of the valence band is dominated by Me 3d bands, while a strong hybridization between C 2p and N 2p states determines the valence band electronic structure away from the top. The 2p contributions from non-equivalent nitrogen sites have been identified using resonant inelastic x-ray scattering spectroscopy with the excitation energy tuned near the N 1s threshold. The binding energy of the Me 3d bands and the hybridization between N 2p and Me 3d states both increase in going across the row from Me = Mn to Me = Cu. Localization of the Cu 3d states also leads to weak screening of Cu 2p and 3s states, which accounts for shifts in the core 2p and 3s spectra of the transition metal atoms. Calculations indicate that the ground-state magnetic ordering, which varies across the series is largely dependent on the occupation of the metal 3d shell and that structural differences in the superexchange pathways for different compounds play a secondary role.Comment: 20 pages, 11 figures, 2 table