title: Determination of spin injection and transport in a ferromagnet/organic semiconductor heterojunction by two-photon photoemission.
abstract: A fundamental prerequisite for the implementation of organic semiconductors (OSCs) in spintronics devices is the still missing basic knowledge about spin injection and transport in OSCs. Here, we consider a model system consisting of a high-quality interface between the ferromagnet cobalt and the OSC copper phthalocyanine (CuPc). We focus on interfacial effects on spin injection and on the spin transport properties of CuPc. Using spin-resolved two-photon photoemission, we have measured directly and in situ the efficiency of spin injection at the cobalt-CuPc interface. We report a spin injection efficiency of 85-90% for injection into unoccupied molecular orbitals of CuPc. Moreover, we estimate an electron inelastic mean free path in CuPc in the range of 1 nm and a 10-30 times higher quasi-elastic spin-flip length. We demonstrate that quasi-elastic spin-flip processes with energy loss < or = 200 meV are the dominant microscopic mechanism limiting the spin diffusion length in CuPc.
authors.affiliation: Department of Physics and Research Center OPTIMAS, University of Kaiserslautern, 67663 Kaiserslautern, Germany. cinchett@rhrk.uni-kl.de
authors.forename: Mirko
authors.initials: M
authors.lastname: Cinchetti
authors.forename: Kathrin
authors.initials: K
authors.lastname: Heimer
authors.forename: Jan-Peter
authors.initials: JP
authors.lastname: Wüstenberg
authors.forename: Oleksiy
authors.initials: O
authors.lastname: Andreyev
authors.forename: Michael
authors.initials: M
authors.lastname: Bauer
authors.forename: Stefan
authors.initials: S
authors.lastname: Lach
authors.forename: Christiane
authors.initials: C
authors.lastname: Ziegler
authors.forename: Yongli
authors.initials: Y
authors.lastname: Gao
authors.forename: Martin
authors.initials: M
authors.lastname: Aeschlimann