Coexistence of Spin-Canting, Metamagnetism, and Spin-Flop in a (4,4) Layered Manganese Azide Polymer

Abstract

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. 1 crystallizes in the monoclinic system, space group P2 1 /c, formula C 8 H 8 N 18 Mn, with a ) 12.2831(4) Å, b ) 6.3680(1) Å, c ) 10.2245(3) Å, β ) 105.064(1)°, and Z ) 2. Bridged by end-to-end azides, the Mn 2+ 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 Mn 2+ ions, and the Nee ´l temperature is T N ) 23.7 K. In the ordered state below T N , detailed investigations on an oriented single-crystal sample of 1 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-H b 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 ≈ -3.5 cm -1 and J a * ) 6 × 10 -4 cm -1 , the anisotropy field H A ) 0.2 kOe, the exchange field H E ) 387.8 kOe, and the anisotropy parameter R ) 5 × 10 -4 . The small J a * and R show 1 to be a good example of a two-dimensional Heisenberg system.

Spin Canting in a Cobalt(II) Radical Complex with an Acentric Counter Anion

“…Assuming that the relaxation time (τ) at the peak-top temperature of χ m ЈЈ in the field of 1300 Oe is well approximated by the inverse of the AC frequency [τ = τ 0 exp(∆/k B )], an Arrhenius plot gave an effective energy barrier for the magnetization reversal of ∆ = 58.6 K and a pre-exponential factor of τ 0 = 2.58 ϫ 10 -16 s. [11] In a magnetic field lower than H c , the residual magnetic moments due to spin canting on the chains are antiferromagnetically coupled to each other, and this affords a hidden-spin canting situation. [12] In a magnetic field equal to H c , on the other hand, the amplitude of the applied magnetic field is comparable to the interchain antiferromagnetic interactions, and 2 showed a slow reversal magnetization such as a single-chain magnet. [13] Figure 5. χ m ЈЈ vs. T plots for 2 with a 3 Oe AC field oscillating at 2-10 kHz: zero (a) and 1300 Oe (b) external magnetic field.…”

Magnetic behaviour in metal-organic frameworks—Some recent examples

“…26 Several highspin Mn +2 complexes with inversion centers exhibiting spin-canted antiferromagnetic behaviour have been reported, which could be due to the weak single-ion anisotropy of the Mn +2 site or anisotropy of the whole crystal. 33 In IV, the adjacent Mn +2 ions are related structurally by a crystallographic inversion center and all the Mn 2 -units appear to be connected by the 2 1 axis. This structural arrangement of the Mn 2 dimers would create differences in the orientation of the Mn 2 -units, and can lead to antisymmetric exchanges resulting in the canting of the spins.…”

Homoleptic manganese(II)–azide layer: Synthesis, structural characterization and magnetic properties

“…Particular interest has been focused on the azido ligand for its diversity in coordination modes and efficiency in magnetic coupling, and a large number of azido-bridged complexes with different dimensionalities and various topologies have been reported in the literature [4][5][6]. These complexes can be divided into two classes besides the neutral binary metal azides [7,8]: (i) heteroleptic complexes with coligands [9][10][11][12][13][14][15][16] and (ii) homoleptic anionic ones with charge-balancing cations that may act as templates for the anionic metal-azide substructures [17][18][19][20][21][22]. Considerable progress has been made in the synthesis and characterization of the former class, but the latter class has been relatively rarely explored.…”

“…1 and the relevant parameters are summarized in Table 1. observations are uncommon, because the single EE-azido bridges usually adopt the asymmetric mode to give relatively inclined metal coordination spheres [5,[9][10][11][12][13][14][15][16]. Such structural characteristics should have impacts on magnetic behaviors, as will be discussed below.…”

“…All the J values lie in the range of 2.2-4.9 cm À1 [9][10][11][12][13][14][15][16]. It is worthwhile to give some remarks on magneto-structural correlations in such systems.…”