Hexagonal-Close-Packed Lattice: Phase Transition and Spin Transport
  We study the ground state (GS) and the phase transition in a hexagonal-close-packed lattice with both XY and Ising models by using extensive Monte Carlo simulation. We suppose the in-plane interaction $J_1$ and inter-plane interaction $J_2$, both antiferromagnetic. The system is frustrated with two kinds of GS configuration below and above a critical value of $\eta=J_1/J_2$ ($\eta_c$). For the Ising case, one has $\eta_c=0.5$ which separates in-plane ferromagnetic and antiferromagnetic states, while for the XY case $\eta_c=1/3$ separates the collinear and non collinear spin configurations. The phase transition is shown to be of first (second) order for $\eta> (<) \eta_c$. The spin resistivity is calculated for the Ising case. It shows a rounded maximum at the magnetic transition in the second-order region, and a discontinuity in the first-order region of $\eta$. 
Danh-Tai Hoang and H. T. Diep
cond-mat.stat-mech