The antiferromagnetic order in an F-AF random alternating quantum spin chain : (CH_3)_2 CHNH_3 Cu(Cl_x Br_{1-x})_3

TL;DR

This study investigates the emergence of uniform antiferromagnetic order in a disordered quantum spin chain with mixed ferromagnetic and antiferromagnetic bonds, revealing that such order can persist despite randomness.

Contribution

It demonstrates through quantum Monte Carlo simulations that uniform AF order can exist in a disordered F-AF spin chain, explaining experimental magnetic phase transitions.

Findings

Uniform AF order observed in intermediate concentration range.

Critical behavior consistent with experimental phase transition.

AF order survives despite random ferromagnetic bonds.

Abstract

A possibility of the uniform antiferromagnetic order is pointed out in an S=1/2 ferromagnetic (F) - antiferromagnetic (AF) random alternating Heisenberg quantum spin chain compound: (CH_3)_2 CHNH_3 Cu(Cl_x Br_{1-x})_3. The system possesses the bond alternation of strong random bonds that take +/- 2J and weak uniform AF bonds of -J. In the pure concentration limits, the model reduces to the AF-AF alternation chain at x=0 and to the F-AF alternation chain at x=1. The nonequilibrium relaxation of large-scale quantum Monte Carlo simulations exhibits critical behaviors of the uniform AF order in the intermediate concentration region, which explains the experimental observation of the magnetic phase transition. The present results suggest that the uniform AF order may survive even in the presence of the randomly located ferromagnetic bonds.