Spinterface and Magnetic Coupling of Tris(8-hydroxyquinoline)iron(III) on Cobalt Surface

Li-Chung Yu^1*, Jiu-Hua Lin^1,2, Yu-Ling Lai¹, Hung-Wei Shiu¹, Yao-Jane Hsu¹

¹Nano Science Group, National Synchrotron Radiation Research Center, Hsinchu, Taiwan
²Program for Science and Technology of Accelerator Light Source, National Chiao Tung University, Hsinchu, Taiwan

* Presenter:Li-Chung Yu, email:red131017@gmail.com

In these two decades, how to inject, manipulate and detect spins in the solid states is a popular field which is named Spintronics and have being to apply to magnetic information storage. It’s well-known that an electron has not only a basic negative charge but also a magnetic momentum. Spintronics utilizes the charge and spin degree of freedom of electrons to extend the capabilities of devices. On the other hand, organic materials are widely used in human life because of diverse organic compounds which could be synthesized via spectacular organic chemical reactions. They have the advantages, such as low cost, light molecular weight, fabrication in large area, tunability of electronic structure, and flexibility with plastic substrates. Due to the its low spin-orbital coupling and hyperfine interaction, organic materials has been well applied in spintronic devices, named as organic spintroncs. Tris(8-hydroxyquinoline)aluminum (Alq₃) with high electron-transport properties and promising emitting material has been successfully sandwiched between two ferromagnetic electrodes as an organic spin valve (OSV) device. The synthesized tris(8-hydroxyquinoline)iron(III) (Feq₃) containing the paramagnetic metal center was deposited on cobalt surface for investigating the magnetic interplay between organic semiconductor Feq₃ and ferromagnetic Co. Our results indicate that the interface interaction between Feq₃ and cobalt is similar to Alq₃ on Co. The nitrogen atoms of pyridyl ring and oxygen atoms of phenoxide ring in Feq₃ show strong hybridization with cobalt by x-ray photoelectron spectroscopy (XPS). However, the chemical states and electronic structure of central iron are significantly affected by the hybridization of anchoring atoms, that is completely different from the case of Alq₃ on ferromagnetic surface. Measurements of x-ray magnetic circular dichroism (XMCD) at Fe and Co L-edge display the same polarity of spin polarization that illustrates a ferromagnetic exchange coupling is between central iron ion and cobalt at the interface. Away from the interface, Feq₃ has no spin polarization with the absence of direct contact to Co. The results indicate that an induced interfacial spin polarization on the iron complex and Co may shed light on the way for an effective spin filtering in organic spintronic devices.

Keywords: Interface, Hybridization, Ferromagnetism, tris(8-hydroxyquinoline)iron(III), cobalt