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arXiv:2312.05544 · Journal of Physics Condensed Matter

Magnetic properties of ferro-antiferromagnetic spin triangle chain

Д. В. Дмитриев, V. Ya. Krivnov

Published Feb 2, 2024• 0 citations
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Abstract

Frustrated spin-12model consisting of a linear chain of triangles with ferro (F)- and antiferromagnetic interactions connected by ferromagnetic interactions (triangles chain) is studied. The ground state phase diagram depending on the interaction ratios consists of ferromagnetic, two ferrimagnetic and singlet phases. The magnetic properties in these phases are analyzed both analytically and numerically. We show that in some regions of the singlet phase the magnetization curves have magnetization plateau and magnetization jumps. We study the thermodynamics and its relation to the specific structure of the excitation spectrum of the triangle chain.

DOI
10.1088/1361-648x/ad258a

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Frustrated spin-12model consisting of a linear chain of triangles with ferro (F)- and antiferromagnetic interactions connected by ferromagnetic interactions (triangles chain) is studied. The ground state phase diagram depending on the interaction ratios consists of ferromagnetic, two ferrimagnetic and singlet phases. The magnetic properties in these phases are analyzed both analytically and numerically. We show that in some regions of the singlet phase the magnetization curves have magnetization plateau and magnetization jumps. We study the thermodynamics and its relation to the specific structure of the excitation spectrum of the triangle chain.
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The frustrated ferromagnetic spin-1∕21∕21∕2 Heisenberg chain is studied by means of a low-energy field theory as well as the density-matrix renormalization group and exact diagonalization methods. First, we study the ground-state phase diagram in a magnetic field and find an ``even-odd'' (EO) phase characterized by bound pairs of magnons in the region of two weakly coupled antiferromagnetic chains. A jump in the magnetization curves signals a first-order transition at the boundary of the EO phase, but otherwise the curves are smooth. Second, we discuss thermodynamic properties at zero field, where we confirm a double-peak structure in the specific heat for moderate frustrating next-nearest-neighbor interactions.
Abstract We study the delta-chain with spin-1 on basal sites and spin- 1 2 on apical sites. The Heisenberg interaction between neighbor basal spins is antiferromagnetic (AF) and the interaction between basal and apical spins is ferromagnetic (F). We show that the magnetization curve of this model is the same as that of the spin- 1 2 kagome-like chain with competing Heisenberg interactions. The ground state phase diagram of the latter as a function of the ratio between the AF and F interaction, α, consists of the ferromagnetic, ferrimagnetic and singlet phases. We study the magnetic properties in each ground state phase and analyze the magnetization curves. We show that there are magnetization plateaus and jumps in definite regions of value α. We compare the magnetic properties of considered models with those of the spin- 1 2 delta chain.
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.
We study the low-energy properties of a sawtooth chain with spin-1's at the bases of the triangles and spin-12′s\frac{1}{2}\mathrm{'}\mathrm{s}21​′sat the vertices of the triangles. The spins have Heisenberg antiferromagnetic interactions between nearest neighbors, with a coupling J2{J}_{2}J2​ between a spin-1 and a spin-12,\frac{1}{2},21​, and a coupling J1=1{J}_{1}=1J1​=1 between two spin-1's. Analysis of the exact diagonalization data for periodic chains containing up to N=12N=12N=12 unit cells shows that the ground state is a singlet for exchange couplings up to approximately J2=3.8,{J}_{2}=3.8,J2​=3.8, whereas for larger J2{J}_{2}J2​ the system exhibits a ferrimagnetic ground state characterized by a net ferromagnetic moment per unit cell of 1/2. In the region of small interactions J2,{J}_{2},J2​, the mixed spin sawtooth chain maps on to an effective isotropic spin model representing two weakly interacting and frustrated spin-12\frac{1}{2}21​ Heisenberg chains composed of spin-12\frac{1}{2}21​ sites at odd and even vertices, respectively. Finally, we study the phenomenon of a macroscopic magnetization jump which occurs if a magnetic field is applied with a value close to the saturation field for J2=2.{J}_{2}=2.J2​=2.
The ground state properties of the S = 1/2 frustrated Heisenberg chain with period 3 exchange modulation are investigated using the numerical diagonalization and density matrix renormalization group (DMRG) method. It is known that this model has a magnetization plateau at one third of the saturation magnetization M s . On the other hand, the ground state is ferrimagnetic even in the absence of frustration if one of the nearest neighbour bond is ferromagnetic and the others are antiferromagnetic. In the present work, we show that this ferrimagnetic state continues to the region in which all bonds are antiferromagnetic if the frustration is strong. This state further continues to the above-mentioned 1/3 plateau state. In between, we also find the noncollinear ferrimagnetic phase in which the spontaneous magnetization is finite but less than M s /3. The intuitive interpretation for the phase diagram is given and the physical properties of these phases are discussed.