Spin-1 triangular lattice Ising model: Consider a ferromagnetic spin-1 triangular lattice Ising model. The Hamiltonian is
H=-J\sum_((:ij:)) S_(i)^(z)S_(j)^(z)-H\sum_i S_(i)^(z)where
S_(i)^(z)in{-1,0,+1}on each site
i,His a uniform magnetic field, and where the first sum is over all links of the lattice. (a) Derive the mean field Hamiltonian
H_(MF)for this model. (b) Derive the free energy per site
f_(MF)within the mean field approach. (c) Derive the self-consistent equation for the local magnetization
m=(:S_(i)^(z):), and find the critical temperature
T_(c)(H)
=(
0). (d) Expand the mean field free energy as
f(m,h)=f_(0)+(t)/(2)m^(2)+um^(4)-hm+O(h^(2),hm^(3),m^(6))Find
f_(0),t,u, and
hin terms of
J,H, and
k_(B)T.