AVS 53rd International Symposium
    Magnetic Interfaces and Nanostructures Thursday Sessions
       Session MI+EM-ThM

Paper MI+EM-ThM7
Characterization of Ferromagnetic Metal/Organic Semiconductor Interfaces in Organic Spin Valves

Thursday, November 16, 2006, 10:00 am, Room 2006

Session: Spin Injection
Presenter: G.J. Szulczewski, University of Alabama
Authors: G.J. Szulczewski, University of Alabama
J. Tang, University of Alabama
W. Xu, University of Alabama
L. Navar, University of Alabama
R. Schad, University of Alabama
A. Gupta, University of Alabama
Correspondent: Click to Email
In the past several years there has been a growing interest in combining ferromagnetic and molecular materials to create organic-based spintronic devices, such as light-emitting diodes and spin-valves. In a vertical device structure one of the processing steps is deposition of a ferromagnetic thin film onto an organic layer. In order to understand the electronic and magnetic nature of these interfaces we have vapor deposited thin films of Co, Fe, and Ni onto 100 nm films of pi-conjugated organic molecules. The molecules studied were aluminum tris(quinolate), tetraphenylporphyrin, phthalocyanine, and perylenetetracarboxylic dianhydride. Using magnetometry techniques the temperature dependent saturation magnetization and coercivity was measured as a function of ferromagnetic metal film thickness. In general several trends were observed. First, in thin ferromagnetic layers less than 3 nm the films did not exhibit a magnetic moment. Second, the Co, Fe and Ni films exhibit ferromagnetic behavior above 3 nm with a coercivity much larger than would be observed for sputter films on Si wafers. Third, the coercivity of Ni and Co films depends on the roughness and functional groups in the molecules more than Fe films, which is attributed to the higher chemical reactivity of Fe atoms. Based on these observations we choose Co films as the top electrode in the fabrication of organic-spin valves because it less reactive than Fe and has a higher coercivity than Ni. Spin-valves were made by depositing Co films onto porphyrin and phthalocyanine organic layers which were first deposited onto La@sub0.67@Sr@sub0.33@MnO@sub3@ substrates. At 80 K the magnetoresistance was measured to be about 20%. The magnetoresistance was found to decrease rapidly with both increasing temperature and voltage bias. The role of the ferromagnetic/organic interfaces on spin-valve performance will be discussed.