[3] First order transition in antiferromagnetic stacked triangular lattices with vector spins

In this article, we show by Monte Carlo simulations that the phase transition is definitely of first order in the antiferromagnetic stacked triangular lattices with both classical $XY$ and Heisenberg spins in a range of the antiferromagnetic next-nearest-neighbor interaction $J_2$. The phase diagram in the ($J_2/J_1$,T) space ($J_1$: nearest-neighbor interaction, T:temperature) is shown and discussed.