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arXiv:1702.03915 · Journal of Physics Condensed Matter

Kagome-like chains with anisotropic ferromagnetic and antiferromagnetic interactions

Д. В. Дмитриев, V. Ya. Krivnov

Published Mar 24, 2017• 6 citations
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Abstract

We consider a spin-[Formula: see text] kagome-like chain with competing ferro- and antiferromagnetic anisotropic exchange interactions. The ground state phase diagram of this model consists of the ferromagnetic and ferrimagnetic phases. We study the ground state and the low-temperature properties on the phase boundary between these phases. The ground state on this phase boundary is macroscopically degenerate and consists of localized magnon states. We calculate the ground state degeneracy and corresponding residual entropy. The spontaneous magnetization has a jump on the phase boundary confirming the first-order type of the phase transition. In the limit of a strong anisotropy, the spectrum of the low-energy excitations has multi-scale structure governing the peculiar features of the specific heat behavior.

DOI
10.1088/1361-648x/aa68f6

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We consider analytically and numerically an anisotropic spin-[Formula: see text] delta-chain (sawtooth chain) in which exchange interactions between apical and basal spins are ferromagnetic and those between basal spins are antiferromagnetic. In the limit of strong anisotropy of exchange interactions this model can be considered as the Ising delta chain with macroscopic degenerate ground state perturbed by transverse quantum fluctuations. These perturbations lift the ground state degeneracy and the model reduces to the basal XXZ spin chain in the magnetic field induced by static apical spins. We show that the ground state of such a model is ferrimagnetic. The excitations of the model are formed by ferrimagnetic domains separated by domain walls with a finite energy. At low temperatures the system is effectively divided into two independent subsystems, the apical subsystem described by the Ising spin-[Formula: see text] chain and the basal subsystem described by the XXZ chain with infinite zz interactions.
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Abstract A quantum spin model of a delta-chain with ferro- and antiferromagnetic exchange interactions has been analyzed. Special attention has been paid to the analysis of magnetic properties at the critical point that separates the ferro- and ferrimagnetic phases of the ground state. The ground state is macroscopically degenerate in this case, and the entropy at zero temperature is finite. The gap in the excitation spectrum is exponentially small, and the spectrum itself has a multiscale structure that determined the low-temperature thermodynamics. The results obtained are used to analyze the magnetic properties of recently synthesized molecules with a record-breaking spin value of the ground state.