26 research outputs found
Ground state of a spin-1/2 Heisenberg-Ising two-leg ladder with XYZ intra-rung coupling
The quantum spin-1/2 two-leg ladder with an anisotropic XYZ Heisenberg
intra-rung interaction and Ising inter-rung interactions is treated by means of
a rigorous approach based on the unitary transformation. The particular case of
the considered model with X-X intra-rung interaction resembles a quantum
compass ladder with additional frustrating diagonal Ising interactions. Using
an appropriately chosen unitary transformation, the model under investigation
may be reduced to a transverse Ising chain with composite spins, and one may
subsequently find the ground state quite rigorously. We obtain a ground-state
phase diagram and analyze the interplay of the competition between several
factors: the XYZ anisotropy in the Heisenberg intra-rung coupling, the Ising
interaction along the legs, and the frustrating diagonal Ising interaction. The
investigated model shows extraordinarily diverse ground-state phase diagrams
including several unusual quantum ordered phases, two different disordered
quantum paramagnetic phases, as well as discontinuous or continuous quantum
phase transitions between those phases.Comment: 8 pages, 4 figure
On the exact solution of the mixed-spin Ising chain with axial and rhombic zero-field splitting parameters
Ground-state phase diagram of the mixed spin- and spin- Ising chain
with axial and rhombic zero-field splitting parameters is exactly calculated
within the framework of the transfer-matrix method. It is shown that the
rhombic zero-field splitting parameter prefers the magnetically ordered phase
instead of the disordered phase.Comment: 5 pages, 2 figure
Low-temperature thermodynamics of spin-1/2 orthogonal-dimer chain with Ising and Heisenberg interactions
We consider an exactly solvable version of the quantum spin-1/2
orthogonal-dimer chain with the Heisenberg intra-dimer and Ising inter-dimer
couplings. The investigated quantum spin system exhibits at zero temperature
fractional plateaux at 1/4 and 1/2 of the saturation magnetization and it has a
highly degenerate ground state at critical fields where the magnetization
jumps. We study the field dependence of the specific heat at low temperature.
The lattice-gas description is formulated in a vicinity of critical fields to
explain the low-temperature behaviour of specific heat.Comment: 2 pages, 1 figure, contribution to proceedings of CSMAG'13 conferenc
Phase transitions of geometrically frustrated mixed spin-1/2 and spin-1 Ising-Heisenberg model on diamond-like decorated planar lattices
Phase transitions of the mixed spin-1/2 and spin-1 Ising-Heisenberg model on
several decorated planar lattices consisting of interconnected diamonds are
investigated within the framework of the generalized decoration-iteration
transformation. The main attention is paid to the systematic study of the
finite-temperature phase diagrams in dependence on the lattice topology. The
critical behaviour of the hybrid quantum-classical Ising-Heisenberg model is
compared with the relevant behaviour of its semi-classical Ising analogue. It
is shown that both models on diamond-like decorated planar lattices exhibit a
striking critical behaviour including reentrant phase transitions. The higher
the lattice coordination number is, the more pronounced reentrance may be
detected.Comment: 11 pages, 5 figure
Towards lattice-gas description of low-temperature properties above the Haldane and cluster-based Haldane ground states of a mixed spin-(1,1/2) Heisenberg octahedral chain
The rich ground-state phase diagram of the mixed spin-(1,1/2) Heisenberg octahedral chain was previously elaborated from effective mixed-spin Heisenberg chains, which were derived by employing a local conservation of a total spin on square plaquettes of an octahedral chain. Here we present a comprehensive analysis of the thermodynamic properties of this model. In the highly frustrated parameter region the lowest-energy eigenstates of the mixed-spin Heisenberg octahedral chain belong to flat bands, which allow a precise description of lowtemperature magnetic properties within the localized-magnon approach exploiting a classical lattice-gas model of hard-core monomers. The present article provides a more comprehensive version of the localized-magnon approach, which extends the range of its validity down to a less frustrated parameter region involving the Haldane and cluster-based Haldane ground states. A comparison between results of the developed localized-magnon theory and accurate numerical methods such as full exact diagonalization and finite-temperature Lanczos technique convincingly evidence that the low-temperature magnetic properties above the Haldane and the cluster-based Haldane ground states can be extracted from a classical lattice-gas model of hard-core monomers and dimers, which is additionally supplemented by a hard-core particle spanned over the whole lattice representing th
Ferrimagnetic spin-1/2 chain of alternating Ising and Heisenberg spins in arbitrarily oriented magnetic field
The ferrimagnetic spin-1/2 chain composed of alternating Ising and Heisenberg
spins in an arbitrarily oriented magnetic field is exactly solved using the
spin-rotation transformation and the transfer-matrix method. It is shown that
the low-temperature magnetization process depends basically on a spatial
orientation of the magnetic field. A sharp stepwise magnetization curve with a
marked intermediate plateau, which emerges for the magnetic field applied along
the easy-axis direction of the Ising spins, becomes smoother and the
intermediate plateau shrinks if the external field is tilted from the easy-axis
direction. The magnetization curve of a polycrystalline system is also
calculated by performing powder averaging of the derived magnetization formula.
The proposed spin-chain model brings an insight into high-field magnetization
data of 3d-4f bimetallic polymeric compound Dy(NO_3)(DMSO)_2Cu(opba)(DMSO)_2,
which provides an interesting experimental realization of the ferrimagnetic
chain composed of two different but regularly alternating spin-1/2 magnetic
ions Dy^{3+} and Cu^{2+} that are reasonably approximated by the notion of
Ising and Heisenberg spins, respectively.Comment: 11 pages, 6 figure