Magnetization plateaus in weakly coupled dimer spin system

TL;DR

This paper investigates magnetization plateaus in a weakly coupled dimer spin system, revealing specific fractional plateaus and their dependence on model parameters, with implications for experimental observations in related materials.

Contribution

It demonstrates the existence of magnetization plateaus at 1/3, 1/2, and 2/3, and predicts possible 1/4 and 3/4 plateaus in three-dimensional structures, extending understanding of quantum spin systems.

Findings

Plateaus at 1/3, 1/2, and 2/3 of saturation magnetization identified.

Perturbative calculations of critical fields for plateau formation.

Potential for 1/4 and 3/4 plateaus in 3D lattice structures.

Abstract

I study a spin system consisting of strongly coupled dimers which are in turn weakly coupled in a plane by zigzag interactions. The model can be viewed as the strong-coupling limit of a two-dimensional zigzag chain structure typical, e.g., for the $(ac)$-planes of KCuCl_3. It is shown that the magnetization curve in this model has plateaus at 1/3 and 2/3 of the saturation magnetization, and an additional plateau at 1/2 can appear in a certain range of the model parameters; the critical fields are calculated perturbatively. It is argued that for the three-dimensional lattice structure of the KCuCl_3 family the plateaus at 1/4 and 3/4 of the saturation can be favored in a similar way, which might be relevant to the recent experiments on NH_4CuCl_3 by Shiramura et al., J. Phys. Soc. Jpn. {\bf 67}, 1548 (1998).