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- Title
MAGNETIC ORDERING OF ANTIFERROMAGNETS ON A SPATIALLY ANISOTROPIC TRIANGULAR LATTICE.
- Authors
BISHOP, R. F.; LI, P. H. Y.; FARNELL, D. J. J.; CAMPBELL, C. E.
- Abstract
We study the spin-1/2 and spin-1 $J_1 - J_2^\prime$ Heisenberg antiferromagnets (HAFs) on an infinite, anisotropic, two-dimensional triangular lattice, using the coupled cluster method. With respect to an underlying square-lattice geometry the model contains antiferromagnetic (J1 > 0) bonds between nearest neighbours and competing $(J_2^\prime\, > \,0)$ bonds between next-nearest-neighbours across only one of the diagonals of each square plaquette, the same diagonal in each square. In a topologically equivalent triangular-lattice geometry the model has two sorts of nearest-neighbour bonds, with $J_{2}' \equiv \kappa J_{1}$ bonds along parallel chains and with J1 bonds providing an interchain coupling. The model thus interpolates between an isotropic HAF on the square lattice at one extreme (κ = 0) and a set of decoupled chains at the other (κ → ∞), with the isotropic HAF on the triangular lattice in between at κ = 1. For the spin-1/2 $J_1 - J_2^\prime$ model, we find a weakly first-order (or possibly second-order) quantum phase transition from a Néel-ordered state to a helical state at a first critical point at κc1 = 0.80 ± 0.01, and a second critical point at κc2 = 1.8 ± 0.4 where a first-order transition occurs between the helical state and a collinear stripe-ordered state. For the corresponding spin-1 model we find an analogous transition of the second-order type at κc1 = 0.62 ± 0.01 between states with Néel and helical ordering, but we find no evidence of a further transition in this case to a stripe-ordered phase.
- Subjects
ANTIFERROMAGNETISM; ANISOTROPY; CRYSTAL lattices; PHASE transitions; QUANTUM theory; MAGNETS; CRITICAL point (Thermodynamics)
- Publication
International Journal of Modern Physics B: Condensed Matter Physics; Statistical Physics; Applied Physics, 2010, Vol 24, Issue 25/26, p5011
- ISSN
0217-9792
- Publication type
Article
- DOI
10.1142/S021797921005716X