Correlation between microstructure and magnetotransport in organic semiconductor spin-valve structures

Yaohua Liu, Shannon M. Watson, Taegweon Lee, Justin M. Gorham, Howard E. Katz, Julie A. Borchers, Howard D. Fairbrother, and Daniel H. Reich
Phys. Rev. B 79, 075312 – Published 12 February 2009

Abstract

We have studied magnetotransport in organic-inorganic hybrid multilayer junctions. In these devices, the organic semiconductor tris(8-hydroxyquinoline) aluminum (Alq3) formed a spacer layer between ferromagnetic (FM) Co and Fe layers. The thickness of the Alq3 layer was in the range of 50–150 nm. Positive magnetoresistance (MR) was observed at 4.2 K in a current perpendicular to plane geometry, and this effect persisted up to room temperature. The devices’ microstructure was studied by x-ray reflectometry, Auger electron spectroscopy, and polarized neutron reflectometry (PNR). The films show well-defined layers with modest average chemical roughness (3–5 nm) at the interface between the Alq3 and the surrounding FM layers. Reflectometry shows that larger MR effects are associated with smaller FM/Alq3 interface width (both chemical and magnetic) and a magnetically dead layer at the Alq3/Fe interface. The PNR data also show that the Co layer, which was deposited on top of the Alq3, adopts a multidomain magnetic structure at low field and a perfect antiparallel state is not obtained. The origins of the observed MR are discussed and attributed to spin-coherent transport. A lower bound for the spin-diffusion length in Alq3 was estimated as 43±5nm at 80 K. However, the subtle correlations between microstructure and magnetotransport indicate the importance of interfacial effects in these systems.

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  • Received 1 October 2008

DOI:https://doi.org/10.1103/PhysRevB.79.075312

©2009 American Physical Society

Authors & Affiliations

Yaohua Liu1, Shannon M. Watson2, Taegweon Lee3, Justin M. Gorham4, Howard E. Katz3, Julie A. Borchers2, Howard D. Fairbrother4, and Daniel H. Reich1,*

  • 1Department of Physics and Astronomy, The Johns Hopkins University, Baltimore, Maryland 21218, USA
  • 2NIST Center for Neutron Research, National Institute of Standards and Technology, Gaithersburg, Maryland 20899, USA
  • 3Department of Materials Science and Engineering, The Johns Hopkins University, Baltimore, Maryland 21218, USA
  • 4Department of Chemistry, The Johns Hopkins University, Baltimore, Maryland 21218, USA

  • *Corresponding author; reich@jhu.edu

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Issue

Vol. 79, Iss. 7 — 15 February 2009

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