Hybrid interface states and spin polarization at ferromagnetic metal-organic heterojunctions: Interface engineering for efficient spin injection in organic spintronics

Abstract

Ferromagnetic metal-organic semiconductor (FM-OSC) hybrid interfaces have been shown to play an important role for spin injection in organic spintronics. Here, 11,11,12,12-tetracyanonaptho-2,6-quinodimethane (TNAP) is introduced as an interfacial layer in Co-OSCs heterojunctions with an aim to tune the spin injection. The Co/TNAP interface is investigated by use of X-ray and ultraviolet photoelectron spectroscopy (XPS/UPS), near edge X-ray absorption fine structure (NEXAFS) and X-ray magnetic circular dichroism (XMCD). Hybrid interface states (HIS) are observed at Co/TNAP interfaces, resulting from chemical interactions between Co and TNAP. The energy level alignment at the Co/TNAP/OSCs interface is also obtained, and a reduction of the hole injection barrier is demonstrated. XMCD results confirm sizeable spin polarization at the Co/TNAP hybrid interface. Hybrid interface states and spin polarization are observed at ferromagnetic metal (FM)-organic interfaces, which result from the chemical interaction and hybridization between the FM and the organic molecules. It provides a way for spinterface engineering in organic spintronics. This approach allows full control of the spin band appropriate for carrier injection, opening up new spintronic device concepts for future exploitation. © 2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.