Coexistence of spin-canting, metamagnetism, and spin-flop in a (4,4) layered manganese azide polymer

A novel molecule-based magnetic polymer Mn(N-3)(2)(btr)(2) 1 (btr = 4,4'-bi-1,2,4-triazole) was synthesized and characterized crystallographically and magnetically. I crystallizes in the monoclinic system, space group P2(1)/c, formula CgH(8)N(18)Mn, with a = 12.283](4) angstrom, b = 6.3680(1) angstrom, c = 10.2245(3) angstrom, beta = 105.064(1)degrees, and Z = 2. Bridged by end-to-end azides, the Mn2+ ions form a two-dimensional layer with (4,4) topology; the layers are further connected to the three-dimensional network by the weak hydrogen bonds between ligands of btr. Magnetic studies on a polycrystalline sample show the existence of strong antiferromagnetic couplings between the adjacent Mn2+ ions, and the Neel temperature is T-N = 23.7 K. In the ordered state below TN, detailed investigations on an oriented single-crystal sample of I reveal that the hidden spin-canting, metamagnetic transition, and spin-flop transition can appear in different circumstances. The ground state is of an antiferromagnet with hidden spin-canting. An external field applied along the b direction parallel to the manganese azide layer can lead to a first-order metamagnetic phase transition, while a spin-flop transition may occur when the field is applied along the a* direction that is perpendicular to the manganese azide layer. Magnetic phase diagrams in both the T-H-a* and the T-HI planes were determined. Possible spin configurations before and after the transitions were proposed. Analyses on the experimental data give the following intrinsic parameters: the intra- and interlayer coupling J approximate to -3.5 cm(-1) and J(a*) = 6 x 10(-4) cm(-1), the anisotropy field H-A = 0.2 kOe, the exchange field H-E 387.8 kOe, and the anisotropy parameter alpha = 5 x 10(-4). The small J(a*) and alpha show 1 to be a good example of a two-dimensional Heisenberg system.