Models Heisenberg model

Polymetallic systems are magnetically coupled. The magnetic coupling in the simple Heisenberg model can be described by the following Hamiltonian (38-40) ... 

Bastardis, R., Guihery, N., and Suaud, N. 2007. Relation between double exchange and Heisenberg model spectra application to the half-doped manganites. Physical Review B 75 132403 (1 1). 

Temperature dependence of magnetic susceptibility of the PF6 salt was measured from 300 to 4 K at 5 T [35], The spin susceptibility of this salt gradually decreases from 300 to 50 K. Below 50 K, the susceptibility exhibits a rapid decrease accompanied by anisotropic temperature dependence, which is an indication of the long-range antiferromagnetic ordering. A one-dimensional Heisenberg model is... 

It would be important to figure out the low energy excitation modes (Nambu-Goldstone modes) built on the ferromagnetic phase. The spin waves are well known in the Heisenberg model [10]. Then, how about our case [32] ... 

The spin distribution in the lower homologue [15 w = 2] was most elegantly studied by Takui et al. (1989) by means of a combination of ENDOR experiments and theoretical calculations within the framework of a generalized UHF Hubbard model (Teki et al., 1987a) and a Heisenberg model (Teki et al., 1987b). The spin distribution obtained is just as expected qualitatively in Fig. 7. 

For a two-qubit isotropic Heisenberg model, there exists thermal entanglement for the antiferromagnetic case and no thermal entanglement for the... 

Figure 6.43 (a) x-T plot of KCuFj (circles) compared with the theoretical plot (solid line) for a one-dimensional Heisenberg model, (b) y-T plot of K2N1F4 (circles) and the theoretical fit (solid line) to a two-dimensional Heisenberg model. 

Figure 1. The two-leg ladder with an AF-Heisenberg model described by two coupling constants J for the links in the legs and J for the vertical rungs.

The coefficients a and b (see Table 3.2) take into account the restrictions in spin dimensionality. For a = b= 1, the Heisenberg model with isotropic exchange interaction and isotropic susceptibility results. The combination of a = 1 and b = 0 yields the strictly anisotropic Ising model, in which the orientation of the spins is restricted to the z-axis. Consequently, the susceptibility is strongly orientation dependent and one needs to differentiate between x" in the direction of the z-axis ( easy axis ) and x perpendicular to z. The molar susceptibilities are then related as... 

Finally, for purposes of comparison, it is useful to have a pi electron model which makes neither the Hiickel nor the VB assumptions about the strength of the electron-electron interaction. Such a model can provide a smooth bridge between the Hiickel and Heisenberg models as the relative strength of the chemical bonding and electron repulsion interactions between electrons are changed. Such a role is played by the Pariser-Parr-Pople (PPP) model [21,22], and its close relative, die Hubbard model [23], The PPP model can be... 

An instructive view of the relation between the spectra of the Htickel model (U=0), the Heisenberg model (U large) and the Hubbard model is provided in Fig. 1. Those states described by the Heisenberg model are all of covalent... 

Full Cl ground state energy of the Heisenberg model (Eq. I-) in units of J... 

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