Generation of Large Moments in a Spin-1 Chain with Random Antiferromagnetic Couplings

TL;DR

This paper investigates a disordered spin-1 chain with mixed interactions, revealing that quantum effects induce ferromagnetic couplings and large magnetic moments at low temperatures, despite all initial couplings being antiferromagnetic.

Contribution

It demonstrates that quantum disorder can generate ferromagnetic couplings and large moments in a spin-1 chain, a phenomenon not seen in classical systems.

Findings

Disorder induces ferromagnetic couplings in the chain.

Large magnetic moments form at low temperatures.

The effect is purely quantum mechanical, with no classical analog.

Abstract

We study the spin-1 chain with nearest neighbor couplings that are rotationally invariant, but include both Heisenberg and biquadratic exchange, with random strengths. We demonstrate, using perturbative renormalization group methods as well as exact diagonalization of clusters, that the system generates ferromagnetic couplings under certain circumstances even when all the bare couplings are antiferromagnetic. This disorder induced instability leads to formation of large magnetic moments at low temperatures, and is a purely quantum mechanical effect that does not have a classical counterpart. The physical origin of this instability, as well as its consequences, are discussed.