Anisotropic ferromagnet on a triangular lattice with antiferromagnetic next-nearest-neighbor interactions

We study the magnetic ordering of an anisotropic Heisenberg ferromagnet on a triangular lattice with antiferromagnetic next-nearest-neighbor interactions by means of the mean field theory and a computer simulation. We find that, as the temperature is decreased, an incommensurate short-range order state and a ferromagnetic long-range phase appear successively. The phase transition between them is of the first order and the relaxation time of the transition is very long. Hence, we suggest that the low temperature phase realized in nature is a domain state in which ferromagnetic domains with various sizes are tangled with each other. We also suggest that the model would be applicable to the compound LiNiO2.