Indirect Spin Exchange Interaction in Substituted Copper Phthalocyanine Crystalline Thin Films

TL;DR

This study investigates the indirect spin exchange mechanism in crystalline copper phthalocyanine thin films using magnetic circular dichroism spectroscopy, revealing temperature-dependent exchange interactions and electronic state contributions.

Contribution

It introduces a novel experimental approach combining MCD spectroscopy and a molecular field model to identify electronic states involved in spin exchange in organic materials.

Findings

Exchange interaction observed below 2 K in specific valence band states.

Enhanced Zeeman splitting and a g-factor of -4 identified.

Method provides a new tool for studying spin interactions in organics.

Abstract

The origins of indirect spin exchange in crystalline thin films of Copper Octabutoxy Phthalocyanine (Cu-OBPc) are investigated using Magnetic Circular Dichroism (MCD) spectroscopy. These studies are made possible by a solution deposition technique which produces highly ordered films with macroscopic grain sizes suitable for optical studies. For temperatures lower than 2 K, the contribution of a specific state in the valence band manifold originating from the hybridized lone pair in nitrogen orbitals of the Phthalocyanine ring, bears the Brillouin-like signature of an exchange interaction with the localized $\textit{d}$-shell Cu spins. A comprehensive MCD spectral analysis coupled with a molecular field model of a $\sigma\pi-d$ exchange analogous to $\textit{sp-d}$ interactions in Diluted Magnetic Semiconductors (DMS) renders an enhanced Zeeman splitting and a modified $\textit{g}$-factor of -4 for the electrons that mediate the interaction. These studies define an experimental tool for identifying electronic states involved in spin-dependent exchange interactions in organic materials.