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

Abstract

The crystallographic and magnetic properties of the Mn͓N(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 ͓N͑CN͒ 2 ͔ 2 (M ϭMn, Fe, Co, Ni͒ 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 ␣ c ϭ142.0(5)°.

Synthesis, Crystal Structures, and Magnetic Properties of Ternary M(II)-Dicyanamide-hydroxypyridine Complexes

“…In recent years, much attention has been devoted to dicyanamide-anion-(dca-) bridged coordination polymers [30][31][32][33][34][35][36][37][38][39][40][41][42] for the large variety of magnetic properties, especially the -M(dca) 2 series of compounds, which have isomorphous rutile-like structure, display ferromagnetism (Co, Ni) [43][44][45][46], spin-canted antiferromagnetism (Cr, Mn, Fe) [47,48], and paramagnetism (Cu) [45,46]. Of further importance, from a structural perspective, when auxiliary L ligands are introduced to the ternary M II -dca-L systems, different coordination architectures, such as mononuclear and dinuclear compounds [49], 1D chains [50][51][52][53][54][55][56][57][58], 2D (4,4) or (6,3) [59][60][61][62][63] sheets, and 3D network topologies [64][65][66][67], could be constructed (Scheme 1).…”

Competing magnetostructural phases in a semiclassical system

“…As a point of comparison, the calculated J value at ambient conditions (−0.12 meV) is in good agreement with the experimental value (−0.07 meV). 34,35 Data Availability Relevant data is available upon request from the corresponding authors, Jan Musfeldt (email: musfeldt@utk.edu) or Jun Hee Lee (email: junhee@u-nist.ac.kr). 30,35,37,38 The color scheme in pressure space matches that in prior figures, and blended areas denote extended transition regimes.…”

“…Within GGA + U this choice gives excellent agreement between the calculated (4.66 μ B ) and experimental magnetic moments (4.65 μ B ). 34 The projector augmented wave potentials 58,59 explicitly include 13 valence electrons for manganese (3p 6 3d 5 4s 2 ), 5 for nitrogen (2s 2 2p 3 ), and 4 for carbon (2s 2 2p 2 ). Structural optimizations were performed for a 22-atom unit-cell with a 6 × 6 × 6 Monkhorst-Pack k-point mesh.…”

“…27 Below T N = 15.9 K, the system is a weakly canted antiferromagnet. 34 Magnetic field drives a spin-flop transition near 0.5 T and a transition to the fully saturated state at 30 T that is supported by dicyanamide distortions. 30 A series of room temperature, pressure-induced structural transitions was recently discovered, 38 although a full pressure-temperature (P-T) phase diagram could not be developed from the data.…”

“…[24][25][26][27][28][29][30][31][32][33] Mn[N(CN) 2 ] 2 is a particularly important member of this series. [34][35][36][37][38] In the Pnnm structure, the Mn(II) centers are connected by soft N≡C-N ligands that act as magnetic superexchange pathways. 27 Below T N = 15.9 K, the system is a weakly canted antiferromagnet.…”