Multiferroicity in spin ice: towards a magnetic crystallography of Tb2Ti2O7 in a field

TL;DR

This paper explores the interplay of multiferroicity and emergent monopoles in spin ice, proposing a magnetic crystallography framework that predicts novel charge crystal phases stabilized by external magnetic fields.

Contribution

It introduces a comprehensive phase diagram for spin ice incorporating various interactions and predicts a bi-layered monopole crystal stabilized by a [110] magnetic field.

Findings

Emergence of a bi-layered monopole crystal phase.

Stability of monopole crystals enhanced by external magnetic fields.

Theoretical explanation of Tb2Ti2O7 ordering in large fields.

Abstract

We combine two aspects of magnetic frustration, multiferroicity and emergent quasi-particles in spin liquids, by studying magneto-electric monopoles. Spin ice offers to couple these emergent topological defects to external fields, and to each other, in unusual ways, making possible to lift the degeneracy underpinning the spin liquid and to potentially stabilize novel forms of charge crystals, opening the path to a "magnetic crystallography". In developing the general phase diagram including nearest-neighbour coupling, Zeeman energy, electric and magnetic dipolar interactions, we uncover the emergence of a bi-layered crystal of singly-charged monopoles, whose stability, remarkably, is strengthened by an external [110] magnetic field. Our theory is able to account for the ordering process of Tb2Ti2O7 in large field for reasonably small electric energy scales.