Entropic magnetic interlayer coupling

TL;DR

This paper introduces a novel entropic magnetic interlayer coupling mechanism in nanostructures, demonstrating long-range interactions mediated by entropy, which could enhance thermal stability in nanomagnetic devices.

Contribution

It proposes a new entropic coupling approach in nanomagnetism, especially in spin ice systems, highlighting the role of entropy in magnetic interactions.

Findings

Entropic interactions are long-ranged in spin ice systems.

Entropic coupling induces torques on magnetization in the thermodynamic limit.

Mutual information characterizes properties of small coupled magnetic systems.

Abstract

Nanomagnetism concerns the engineering of magnetic interactions in heterostructures that consist of layers of magnetic and non-magnetic materials. Mostly, these interactions are dominated by the minimization of energy. Here, we propose an effective magnetic interlayer coupling that is dominated by the maximization of entropy. As an example, we consider the system that mediates the effective interactions to be square spin ice, in which case we find purely entropic interactions that are long-ranged. We argue that in the thermodynamic limit the entropic interlayer coupling gives rise to entropic torques on the magnetization direction. For small systems, the physical properties are well characterized by the mutual information between the two magnets that are coupled. Because entropic interactions become stronger for higher temperatures, our findings may benefit the development of nanomagnetic devices that require thermal stability.