High Temperature Molecular Magnetism Caused by pi-electrons: Copper Phthalocyanine Doped with Alkaline Metals

TL;DR

This study reveals high-temperature ferromagnetism in copper phthalocyanine doped with alkaline metals, driven by pi-electrons and explained through the Zener double exchange mechanism, expanding understanding of organic magnetic materials.

Contribution

It demonstrates ferromagnetic behavior in AxCuPc at high temperatures and explains it via the Zener double exchange mechanism, a novel insight for organic magnets.

Findings

Ferromagnetic behavior observed above 77K.

Curie-Weiss temperature varies with stoichiometry.

Magnetism caused by unpaired pi-electrons on phthalocyanine anions.

Abstract

Electron spin resonance spectra of copper phthalocyanine doped with alkaline metals (AxCuPc) have been investigated. The temperature dependence of ESR spectra indicates the ferromagnetic behavior. The Curie-Weiss temperature varies from 30K to 115K depending on the stoichiometry x of samples. Some particles of polycrystalline samples were attracted to a weak magnet at temperature slightly higher than 77K. The observed magnetism is caused by unpaired pi-electrons of phthalocyanine anions on the Eg doubly degenerated molecular orbital. The observed ferromagnetism can be understood within the framework of the McConnell-2 model proposed for organic ferromagnetic charge-transfer complexes. The high-temperature magnetism in AxCuPc is considered to be a result of the Zener mechanism of double exchange between phthalocyanine molecular anions of different valence.