Rod magnets inscribed in an elastic cuboid: interpreting single-domain ferroics in Onsager's spirit

TL;DR

This paper introduces a minimalistic toy model for ferroic orders based on entropy, exhibiting hysteresis and phase transitions similar to single-domain magnets, inspired by Onsager's hard-rod model.

Contribution

It presents a novel entropy-based toy model that captures ferroic behaviors, including hysteresis and phase transitions, with features reminiscent of single-domain magnets and Onsager's theory.

Findings

Model exhibits hysteresis and isotropic-nematic transitions.

Uniaxial anisotropy similar to Stoner-Wohlfarth magnet.

Reliable spin toggling due to two-well energy landscapes.

Abstract

A toy model for ferroic orders through entropy. As the rod/spin concentration (or the volume enclosing the ferroic rods) is variable by a tunable force conjugate to the order parameter, the model exhibits hysteresis associated to some discontinuous isotropic-nematic transitions explained essentially by Onsager's hard-rod model. The uniaxial anisotropy and nonperiodicity by construction is reminiscent of Stoner-Wohlfarth's single-domain magnet, and the toy model may ultimately be seen as a minimalistic for hard ferroics with some possible self-averaging disorders. Spin togglings shall be reliable due to the clean two-well energy landscapes in the athermal transition theory.