Thermodynamics of Spin-1/2 AF-AF-F and F-F-AF Trimerized Quantum Heisenberg Chains

TL;DR

This study investigates the thermodynamic properties of spin-1/2 trimerized quantum Heisenberg chains using TMRG and MSW methods, revealing magnetization plateaus, excitation spectra, and fitting models that match experimental data.

Contribution

It provides a combined TMRG and MSW analysis of thermodynamic behaviors in trimerized chains, highlighting excitation spectra and fitting models for susceptibility and heat capacity.

Findings

Magnetization plateau at m=1/6 observed at low temperature.

Susceptibility and heat capacity fitted by superposition of double two-level systems.

Identification of three branch excitations, including gapless and gapful modes.

Abstract

The magnetization process, the susceptibility and the specific heat of the spin-1/2 AF-AF-F and F-F-AF trimerized quantum Heisenberg chains have been investigated by means of the transfer matrix renormalization group (TMRG) technique as well as the modified spin-wave (MSW) theory. A magnetization plateau at $m=1/6$ for both trimerized chains is observed at low temperature. The susceptibility and the specific heat show various behaviors for different ferromagnetic and antiferromagnetic interactions and in different magnetic fields. The TMRG results of susceptibility and the specific heat can be nicely fitted by a linear superposition of double two-level systems, where two fitting equations are proposed. Three branch excitations, one gapless excitation and two gapful excitations, for both systems are found within the MSW theory. It is observed that the MSW theory captures the main characteristics of the thermodynamic behaviors at low temperatures. The TMRG results are also compared with the possible experimental data.