Indirect Spin Exchange Interaction in Substituted Copper Phthalocyanine Crystalline Thin Films

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 $\text{d}$-shell Cu spins. A comprehensive MCD spectral analysis coupled with a molecular field model of a $\sigma \pi -d$ exchange analogous to $\text{sp-d}$ interactions in Diluted Magnetic Semiconductors (DMS) renders an enhanced Zeeman splitting and a modified $\text{g}$-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.

arXiv commentunder review with Nature:Scientific Reports

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