How does an Ultrathin Cobalt Film Response to the Presence of a Neighboring Pentacene Layer
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1198-E03-08
How does an Ultrathin Cobalt Film Response to the Presence of a Neighboring Pentacene Layer Yuet-Loy Chan1, Ya-Jyuan Hung1,2, Chia-Hao Wang1,2, Ying-Chang Lin1, Ching-Yuan Chiu1, Yu-Ling Lai1, Hsu-Ting Chang1,2, Chih-Hao Lee2, Y. J. Hsu1,3, and D. H. Wei1 1 National Synchrotron Radiation Research Center, Hsinchu 30076, Taiwan. 2 Department of Engineering and System Science, National Tsing Hua University, Hsinchu 30013, Taiwan 3 Institute of Electro-Optical Science and Engineering, National Cheng Kung University, Tainan 70101, Taiwan
ABSTRACT The interfacial regimes of cobalt/pentacene/cobalt (Co/Pc/Co) trilayers were emulated through the ultrathin pentacene/cobalt (Pc/Co) and cobalt/pentacene (Co/Pc) bilayers. Employing the magneto-optical Kerr effect (MOKE) measurement, we found the coercivity of Co bottom film in a thickness of 3.4 nm experienced a slight reduction upon the adsorption of Pc molecules. For the bilayers prepared with reversed order of deposition, the Co film deposited on a 6.4 nm Pc layer showed no observable ferromagnetic order at room temperature until its thickness reached 3 nm. After the onset of magnetic order, the x-ray images acquired on Pc/Co revealed a complicated magnetization patterns comparing to those observed on Co/Pc bilayers. Because the spin-polarized carriers will interact with the environment along their transport path, the presence of a non-magnetic layer and the occurrence of complicated domain structures suggested the spinpolarized carriers would experience a greater disturbance on their spin coherence when crossing the Pc/Co interface.
INTRODUCTION One recent development in spintronics is the incorporation of organic materials to take advantage of their weak spin-orbit coupling that low-Z materials possess. The concept is straightforward; a hybrid structure consisted of an organic layer sandwiched between two ferromagnetic films should be able to maintain a detectable magnetoresistance (MR) while enjoying less constraint in their fabrication.[1-3] However, early experimental results on vertical spin-valve structure; La0.67Sr0.33MnO3/Alq3/Co [4] and Fe/Alq3/Co [5], indicated that the MR of both hybrid trilayers decreased rapidly as the temperature was raised to room temperature. Because MR is the change in electrical resistance of a material when an external magnetic field is applied, the decrease in MR implies the population of spin-polarized carriers is diminished within the structures. Considering the Curie temperature of La0.67Sr0.33MnO3, Fe and Co are all above 300 K, the lost of MR was suggested to associate with a modified spin injection mechanism at the interface separating ferromagnetic electrode and organic spacer.[5] In this study, we focus on studying how a ferromagnetic film would response to the presence of an adjacent organic layer through macroscopic and microscopic investigations. Since a vertical spin-valve involves two interfaces, special attention was paid to examine the possible differences triggered by the opposite order of deposition.
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