Heisenberg chain

Key words ESR, EPR, Heisenberg chain, Haldane, spin-Peierls, large-D, low-dimensional spin systems... 

Here, we report on high-field ESR properties of the 5=1 Heisenberg chain system Ni(C2H8N2)2Ni(CN)4 (NENC) [16,31], This material is characterized by strong in-plane anisotropy D/k= 6 K, and so far can be considered as the best known candidate for a quantum 5=1 chain in the large-D limit (D/J=1.5) [32],... 

J. L. Dye, Electrides From LD Heisenberg chains to 2D pseudo-metals. Inorg. Chem. 36, 3816-26 (1997). 

Table 1 Long-range spin-pairing order p as defined by Eq. (23) of the RVB ansatz and the energy per site in units of J for the linear spin-1/2 Heisenberg chain with nearest- and next-nearest-neighbor spin interactions yield by the M = 5 bonds RVB ansatz with SP parterns of Eqs. (54)-(56) and the M = 5 sites NSBA ansatz with the spin-flip paterns of Eqs. (16)-(18). The lower and upper bounds and the extrapolated results from finite systems of van den Broek et al. [26], the exact results at a = 0 of Hulthen [19] and at a = 0.5 of Majumdar [25] have been included for comparison. At a = 0.5 the RVB ansatz yield the exact result p(J = 1/2) = 3/16.

Extensions to more sophisticated 1-D magnetisms have been performed by Takeuchi22 for 1-D helicoidal systems, and by Duffy and Barr23) for alternating Heisenberg chains (two different exchange integrals). 

Fig. 5. Theoretical susceptibility of a Heisenberg chain for different spin values...

Hydrates. A2MnmF5 H20 compounds (A = K, Rb, Cs) are suitable examples of Heisenberg chain antiferromagnets. The 1-D behavior is enhanced by the ferrodistortive ordering of dj2 orbitals, antiparallel along the c direction. In the ab plane weak d°2 y2 interactions occur between the chains. 

The computed values for a linear alternate Heisenberg chain of S = ... 

Bu4N)[Ni(chdt)2] Sandwiched stmcture AFM 1-D Heisenberg chain 85... 

Fig. 17. Free energy (F), entropy (S) and specific heat (C) of an A = 10 site antiferromagnetic Heisenberg chain. Solid line correspond to the MC results, indistinguishable from the dotted lines for the exact results. Also shown is the relative error s F) of F compared to the exact result...

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