Half-magnetization plateau in a Heisenberg antiferromagnet on a triangular lattice

Abstract

We present the phase diagram in a magnetic field of a 2D isotropic Heisenberg antiferromagnet on a triangular lattice. We consider spin-$S$ model with nearest-neighbor ($J_1$) and next-nearest-neighbor ($J_2$) interactions. We focus on the range of $1/8<J_2/J_1<1$, where the ordered states are different from those in the model with only nearest neighbor exchange. A classical ground state in this range has four sublattices and is infinitely degenerate in any field. The actual order is then determined by quantum fluctuations via "order from disorder" phenomenon. We argue that the phase diagram is rich due to competition between competing four-sublattice quantum states which break either ${\mathbb{Z}}_3$ orientational symmetry or ${\mathbb{Z}}_4$ sublattice symmetry. At small and high fields, the ground state is a ${\mathbb{Z}}_3$-breaking canted stripe state, but at intermediate fields the ordered states break ${\mathbb{Z}}_4$ sublattice symmetry. The most noticeable of such states is "three up, one down" state in which spins in three sublattices are directed along the field and in one sublattice opposite to the field. Such a state breaks no continuous symmetry and has gapped excitations. As the consequence, magnetization has a plateau at exactly one half of the saturation value. We identify gapless states, which border the "three up, one down" state and discuss the transitions between these states and the canted stripe state.

6+8 pages, 4+3 figures

References in corpus (16)

• Spin liquid phase of the $S=\frac{1}{2}$ $J_1-J_2$ Heisenberg model on the triangular lattice
• Unusual ordered phases of highly frustrated magnets: a review
• Magnetization plateaus in frustrated antiferromagnetic quantum spin models
• Quantum stabilization of 1/3-magnetization plateau in Cs_2CuBr_4
• The phase diagram of the antiferromagnetic XXZ model on the triangular lattice
• Microscopic Model Calculations for the Magnetization Process of Layered Triangular-Lattice Quantum Antiferromagnets
• Quasiclassical magnetic order and its loss in a spin-1/2 Heisenberg antiferromagnet on a triangular lattice with competing bonds
• Ground States of Spin-1/2 Triangular Antiferromagnets in a Magnetic Field
• Ground states of a frustrated spin-1/2 antifferomagnet: Cs_2CuCl_4 in a magnetic field
• Charge disproportionation and collinear magnetic order in the frustrated triangular antiferromagnet AgNiO2
• Phases of triangular lattice antiferromagnet near saturation
• Thermodynamics of the Up-Up-Down Phase of the S = 1/2 Triangular-Lattice Antiferromagnet Cs${}_2$CuBr${}_4$
• Competition between supersolid phases and magnetisation plateaux in the frustrated easy-axis antiferromagnet on a triangular lattice
• Spin dynamics of frustrated easy-axis triangular antiferromagnet 2H-AgNiO2 explored by inelastic neutron scattering
• Cascade of field-induced magnetic transitions in a frustrated antiferromagnetic metal
• Supersolid phases in a realistic three-dimensional spin model

Cited by in corpus (4)

• Frustrated two dimensional quantum magnets
• Survival of itinerant excitations and quantum spin state transitions in YbMgGaO${}_4$ with chemical disorder
• Pressure-tuning the quantum spin Hamiltonian of the triangular lattice antiferromagnet Cs${}_2$CuCl${}_4$
• Magnetization plateau and supersolid phases in the spin-1/2 antiferromagnetic Heisenberg model on a tetragonally distorted fcc lattice