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38173-AC5
Spin-Dependent Effects in Ferromagnet/Pi-Conjugated Material Hybrid Systems

Jing Shi, University of California, Riverside

We have explored fabrication of hybrid spin-dependent devices using several carbon-based materials and ferromagnetic oxides such as La_1-xSr_xMnO₃ or LSMO. The interfaces between pi-conjugated organic materials and ferromagnetic oxides have been shown to be particularly suitable for spin injection and detection previously by our group. We extended the study to carbon nanotubes (CNT), graphene and polymers (e.g. P3HT). Our specific objective was to fabricate lateral spin injection devices using ferromagnetic oxide as electrodes. We have succeeded in fabricating ferromagnetic oxide electrodes using pulsed laser deposition, following by photo-lithography and then by focused ion beam. Small gaps (between two LSMO electrodes) down to 150 nm were obtained. These lateral electrodes were connected with carbon nanotubes first. We found that the interfacial resistance dominates the total device resistance in unannealed devices. Upon annealing, the resistance drops sharply at all temperatures. The highest temperature for annealing was found to be about 400 C (in vacuum). The interfacial resistance decreases by several (3-4) orders of magnitude at low temperatures (down to 4K). This dramatically improved interfacial resistance indicates that annealing is very important for cleaning the CNT/metal contacts. However, we have not observed magnetoresistance due to the lateral spin valve effect as reported by Heuso et al. in Nature in 2007. To further study the effect, we have fabricated an array of electrodes with different gap sizes. We are in the process of fabricating CNT arrays using focused ion beam. Meanwhile, we are working on ferromagnetic oxide/graphene interfaces for lateral spin valve devices.

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