Spin Order and Entropy in Antiferromagnetic Films Subjected to Magnetic Fields

TL;DR

This paper uses effective field theory to analyze how magnetic and staggered fields influence the entropy and spin order in antiferromagnetic films, revealing complex order-disorder phenomena at low temperatures.

Contribution

It provides low-temperature series for entropy density and investigates subtle order-disorder phenomena induced by external fields in bipartite antiferromagnets.

Findings

Entropy density series up to two-loop order

Counterintuitive order-disorder phenomena observed

Results applicable to various bipartite 2D lattices

Abstract

Using systematic effective field theory, we explore the properties of antiferromagnetic films subjected to magnetic and staggered fields that are either mutually aligned or mutually orthogonal. We provide low-temperature series for the entropy density in either case up to two-loop order. Invoking staggered, uniform and sublattice magnetizations of the bipartite antiferromagnet, we investigate the subtle order-disorder phenomena in the spin arrangement, induced by temperature, magnetic and staggered fields -- some of which are quite counterintuitive. In the figures we focus on the spin-$\frac{1}{2}$ square-lattice antiferromagnet, but our results are valid for any other bipartite two-dimensional lattice.