Study of an Antiferromagnetic Sawtooth Chain with Spin-1/2 and Spin-1 sites

TL;DR

This paper investigates the low-energy properties of a mixed spin sawtooth chain with spin-1 and spin-1/2 sites, revealing ground state transitions, effective spin models, and magnetization jumps under magnetic fields.

Contribution

It provides a detailed analysis of the phase diagram and magnetic properties of a mixed spin sawtooth chain, including the mapping to an effective spin model and the magnetization jump phenomenon.

Findings

Ground state is a singlet for J_2 up to ~3.8.

System exhibits ferrimagnetic ground state for larger J_2.

Macroscopic magnetization jump occurs near saturation field for J_2=2.

Abstract

We study the low-energy properties of a sawtooth chain with spin-1's at the bases of the triangles and spin-1/2's at the vertices of the triangles. The spins have Heisenberg antiferromagnetic interactions between nearest neighbors, with a coupling J_2 between a spin-1 and a spin-1/2, and a coupling J_1 = 1 between two spin-1's. Analysis of the exact diagonalization data for periodic chains containing up to N=12 unit cells shows that the ground state is a singlet for exchange couplings up to approximately J_2 = 3.8, whereas for larger J_2, 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 J_2, the mixed spin sawtooth chain maps on to an effective isotropic spin model representing two weakly interacting and frustrated spin-1/2 Heisenberg chains composed of spin-1/2 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 J_2 = 2.