Thermodynamic Properties of Heisenberg Ferrimagnetic Spin Chains: Ferromagnetic-Antiferromagnetic Crossover

TL;DR

This paper investigates the thermodynamic behavior of a one-dimensional Heisenberg ferrimagnet with spins 1 and 1/2, revealing a crossover from ferromagnetic to antiferromagnetic behavior across temperature ranges.

Contribution

It introduces a combined use of modified spin-wave theory and quantum Monte Carlo methods to analyze the thermodynamics of ferrimagnetic chains, highlighting the ferromagnetic-antiferromagnetic crossover.

Findings

Specific heat scales as T^{1/2} at low temperatures

Susceptibility diverges as T^{-2} at low temperatures

Model exhibits ferromagnetic behavior at low T and gapped antiferromagnetic at mid T

Abstract

We study thermodynamic properties of the one-dimensional Heisenberg ferrimagnet with antiferromagnetically exchange-coupled two kinds of spins 1 and 1/2. The specific heat and the magnetic susceptibility are calculated employing a modified spin-wave theory as well as a quantum Monte Carlo method. The specific heat is in proportion to $T^{1/2}$ at low enough temperatures but shows a Schottky-like peak at mid temperatures. The susceptibility diverges as $T^{-2}$. We reveal that at low temperatures the model is regarded as a ferromagnet, while at mid temperatures it behaves like a gapped antiferromagnet.