Nematic, vector-multipole, and plateau-liquid states in the classical O(3) pyrochlore antiferromagnet with biquadratic interactions in applied magnetic field

TL;DR

This paper investigates the complex magnetic phases of a classical pyrochlore antiferromagnet with biquadratic interactions, revealing hidden orders and explaining how long-range order emerges from local correlations, with implications for experimental materials.

Contribution

It uncovers nematic and vector-multipole orders in Coulomb phases and clarifies the emergence of long-range order from local correlations in the model.

Findings

Identification of nematic and vector-multipole orders in Coulomb phases

Explanation of how long-range Neel order emerges from local correlations

Implications for magnetic properties of Cr spinels with half-magnetization plateaux

Abstract

The classical bilinear-biquadratic nearest-neighbor Heisenberg antiferromagnet on the pyrochlore lattice does not exhibit conventional Neel-type magnetic order at any temperature or magnetic field. Instead spin correlations decay algebraically over length scales r ~ \sqrt{T}, behavior characteristic of a Coulomb phase arising from a strong local constraint. Despite this, its thermodynamic properties remain largely unchanged if Neel order is restored by the addition of a degeneracy-lifting perturbation, e.g., further neighbor interactions. Here we show how these apparent contradictions can be resolved by a proper understanding of way in which long-range Neel order emerges out of well-formed local correlations, and identify nematic and vector-multipole orders hidden in the different Coulomb phases of the model. So far as experiment is concerned, our results suggest that where long range interactions are unimportant, the magnetic properties of Cr spinels which exhibit half-magnetization plateaux may be largely independent of the type of magnetic order present.