Flat-Band Ferromagnetism in Organic Polymers Designed by a Computer Simulation

TL;DR

This study combines first-principles calculations and Hubbard model analysis to identify poly-aminotriazole as a promising organic polymer exhibiting stable flat-band ferromagnetism, even away from half-filling.

Contribution

It demonstrates the effectiveness of computational methods in designing organic polymers with stable flat-band ferromagnetism, highlighting poly-aminotriazole as a prime candidate.

Findings

Poly-aminotriazole is the best candidate for flat-band ferromagnetism.

Ferromagnetism remains stable when band filling varies from half-filling.

The study provides insights into designing organic ferromagnetic materials.

Abstract

By coupling a first-principles, spin-density functional calculation with an exact diagonalization study of the Hubbard model, we have searched over various functional groups for the best case for the flat-band ferromagnetism proposed by R. Arita et al. [Phys. Rev. Lett. {\bf 88}, 127202 (2002)] in organic polymers of five-membered rings. The original proposal (poly-aminotriazole) has turned out to be the best case among the materials examined, where the reason why this is so is identified here. We have also found that the ferromagnetism, originally proposed for the half-filled flat band, is stable even when the band filling is varied away from the half-filling. All these make the ferromagnetism proposed here more experimentally inviting.