Quantum fluctuation effects on the ordered moments in a two dimensional frustrated ferrimagnet (original) (raw)
Related papers
2012
Quantum corrections of the biquadratic interaction in the 1D spin-1/2 frustrated ferromagnetic Heisenberg model are studied. The biquadratic interaction for spin-1/2 chains is eliminated and transformed to the quadratic interaction. Doing a numerical experiment, new insight as to how the classical phases get modified on the inclusion of quantum fluctuations is provided. Observed results suggest the existence of an intermediate region in the ground state phase diagram of the frustrated ferromagnetic spin-1/2 chains with combination of dimer and chiral orders. In addition, from the quantum entanglement view point, differences between quantum phases are also obtained. The nearest neighbor spins never be entangled in the frustrated ferromagnetic chains but are entangled up to the Majumdar-Ghosh point in the frustrated antiferromagnetic chains. On the other hand, the next nearest neighbor spins in the mentioned intermediate region are entangled.
2009
We have studied the two-dimensional S=1/2 square-lattice antiferromagnet Cu(pz)2(ClO4)2 using neutron inelastic scattering and series expansion calculations. We show that the presence of antiferromagnetic next-nearest neighbor interactions enhances quantum fluctuations associated with resonating valence bonds. Intermediate magnetic fields lead to a selective tuning of resonating valence bonds and a spectacular inversion of the zone-boundary dispersion, providing novel insight into 2D antiferromagnetism in the quantum limit.
Spin wave analysis of square lattice anisotropic frustrated Heisenberg quantum antiferromagnet
The spin 1/2 anisotropic frustrated Heisenberg quantum antiferromagnet was introduced by Nersesyan and Tsvelik a few years ago. We have applied linear spin wave theory to this model to study quantum phase transition as a function of frustrating interactions and anisotropy. This model is known to have two unique classical ground states (Neel and collinear) where long range order survives the quantum fluctuations. Ground state properties including energy, sub-lattice magnetization and static spin-spin correlation functions are calculated to linear order in spin wave theory. The ordered ground states are separated by a disordered phase. We find that the disordered ground state has unbroken rotational symmetry. * Electronic address: ss2010@netzero.com
Physical Review B, 2012
We study the ground-state (GS) properties of the frustrated spin-1 2 J 1-J 2-J 3 Heisenberg model on the two-dimensional honeycomb lattice with ferromagnetic nearest-neighbor (J 1 = −1) exchange and frustrating antiferromagnetic next-nearest-neighbor (J 2 > 0) and next-next-nearest-neighbor (J 3 > 0) exchanges, for the case J 3 = J 2. We use the coupled-cluster method implemented to high orders of approximation, complemented by the Lanczos exact diagonalization of a large finite lattice with 32 sites, in order to calculate the GS energy, magnetic order parameter, and spin-spin correlation functions. In one scenario we find a quantum phase transition point between regions characterized by ferromagnetic order and a form of antiferromagnetic ("striped") collinear order at J c 2 ≈ 0.1095 ± 0.0005, which is below the corresponding hypothetical transition point at J cl 2 = 1 7 (≈0.143) for the classical version of the model, in which we momentarily ignore the intervening noncollinear spiral phase in the region 1 10 < J 2 < 1 5. Hence we see that quantum fluctuations appear to stabilize somewhat the collinear antiferromagnetic order in preference to the ferromagnetic order in this model. We compare results for the present ferromagnetic case (with J 1 = −1) to previous results for the corresponding antiferromagnetic case (with J 1 = +1). The magnetic order parameter is found to behave similarly for the ferromagnetic and the antiferromagnetic models for large values of the frustration parameter J 2. However, there are considerable differences in the behavior of the order parameters for the two models for J 2 /|J 1 | 0.6. For example, the quasiclassical collinear magnetic long-range order for the antiferromagnetic model (with J 1 = +1) breaks down at J c 2 2 ≈ 0.60, whereas the "equivalent" point for the ferromagnetic model (with J 1 = −1) occurs at J c 2 ≈ 0.11. Unlike in the antiferromagnetic model (with J 1 = +1), where a plaquette valence-bond crystal phase intrudes between the two corresponding quasiclassical antiferromagnetic phases (with Néel and striped order) for J c 1 2 < J 2 < J c 2 2 , with J c 1 2 ≈ 0.47, we find no clear indications at all in the ferromagnetic model for an intermediate magnetically disordered phase between the corresponding phases exhibiting ferromagnetic and striped order. Instead the evidence for the ferromagnetic model (with J 1 = −1) points to one of two scenarios: either there is a direct first-order transition between the two magnetically ordered phases, as mentioned above; or there exists an intervening phase between them in the very narrow range 0.10 J 2 0.12, which is probably a remnant of the spiral phase that exists in the classical counterpart of the model over the larger range 1 10 < J 2 < 1 5 .
Two-dimensional anisotropic Heisenberg antiferromagnet in a magnetic field
Physical Review B, 2005
The classical, square lattice, uniaxially anisotropic Heisenberg antiferromagnet in a magnetic field parallel to the easy axis is studied using Monte Carlo techniques. The model displays a longrange ordered antiferromagnetic, an algebraically ordered spin-flop, and a paramagnetic phase. The simulations indicate that a narrow disordered phase intervenes between the ordered phases down to quite low temperatures. Results are compared to previous, partially conflicting findings on related classical models as well as the quantum variant with spin S=1/2.
Journal of the Physical Society of Japan, 2013
The spin-1/2 ferromagnetic-antiferromagnetic alternating Heisenberg chain with ferromagnetic nextnearest-neighbour (NNN) interaction is investigated. The ground state is the Haldane phase for weak NNN interaction, and is the ferromagnetic phase for weak antiferromagnetic interaction. We find a series of topologically distinct spin-gap phases with various magnitudes of edge spins for strong NNN interaction. The phase boundaries between these phases are determined on the basis of the DMRG calculation with additional spins that compensate the edge spins. It is found that each of the exact solutions with short-range antiferromagnetic correlation on the ferromagnetic-nonmagnetic phase boundary is representative of each spin gap phase.
Frustrated spin-1/2 Heisenberg antiferromagnet on a chevron-square lattice
Physical Review B, 2013
The coupled cluster method (CCM) is used to study the zero-temperature properties of a frustrated spin-half (s = 1 2) J1-J2 Heisenberg antiferromagnet (HAF) on a two-dimensional (2D) chevron-square lattice. On an underlying square lattice each site of the model has 4 nearestneighbor exchange bonds of strength J1 > 0 and 2 frustrating next-nearest-neighbor (diagonal) bonds of strength J2 ≡ κJ1 > 0, such that each fundamental square plaquette has only one diagonal bond. The diagonal J2 bonds are arranged in a chevron pattern such that along one of the two basic square axis directions (say, along rows) the J2 bonds are parallel, while along the perpendicular axis direction (say, along columns) alternate J2 bonds are perpendicular to each other, and hence form one-dimensional (1D) chevron chains in this direction. The model thus interpolates smoothly between 2D HAFs on the square (κ = 0) and triangular (κ = 1) lattices, and also extrapolates to disconnected 1D HAF chains (κ → ∞). The classical (s → ∞) version of the model has collinear Néel order for 0 < κ < κ cl and a form of noncollinear spiral order for κ cl < κ < ∞, where κ cl = 1 2. For the s = 1 2 model we use both these classical states, as well as other collinear states not realized as classical ground-state (GS) phases, as CCM reference states, on top of which the multispin-flip configurations resulting from quantum fluctuations are incorporated in a systematic truncation hierarchy, which we carry out to high orders and then extrapolate to the physical limit. At each order we calculate the GS energy, GS magnetic order parameter, and the susceptibilities of the states to various forms of valence-bond crystalline (VBC) order, including plaquette and two different dimer forms. We find strong evidence that the s = 1 2 model has two quantum critical points, at κc 1 ≈ 0.72(1) and κc 2 ≈ 1.5(1), such that the system has Néel order for 0 < κ < κc 1 , a form of spiral order for κc 1 < κ < κc 2 that includes the correct three-sublattice 120 • spin ordering for the triangular-lattice HAF at κ = 1, and parallel-dimer VBC order for κc 2 < κ < ∞.
Physical Review B, 2001
We study the dynamical response of frustrated, quasi-one-dimensional spin-12 Heisenberg antiferromagnets at finite temperatures. We allow for the presence of a Dzyaloshinskii-Moriya interaction. We concentrate on a model of weakly coupled planes of anisotropic triangular lattices. Combining exact results for the dynamical response of one-dimensional Heisenberg chains with a random-phase approximation in the frustrated interchain couplings, we calculate the dynamical susceptibility in the disordered phase. We investigate the instability of the disordered phase to the formation of collective modes. We find a very weak instability to the formation of incommensurate magnetic order and determine the ordering temperature and wave vector. We also determine the effects of uniform magnetic fields on the ordering transition.