Visualizing Spin-Polarization in Nanoislands and Single Molecules with Spin-Polarized STM
Yu-Hsun Chu1*, Chuang-Han Hsu1, Chun-I Lu1, Hung-Hsiang Yang1, Tsung-Han Yang1, Szu-Wei Chen1, Pin-Jui Hsu1, Chao-Cheng Kaun2,3, Germar Hoffmann1,3, Minn-Tsong Lin1,4
1Department of Physics, National Taiwan University, Taipei, Taiwan
2Research Center for Applied Sciences, Academia Sinica, Taipei, Taiwan
3Department of Physics, National Tsing Hua University, Hsinchu, Taiwan
4Institute of Atomic and Molecular Sciences, Academia Sinica, Taipei, Taiwan
* presenting author:Yu-Hsun Chu,
During pursuit of novel spintronic devices, one of the central concepts is to uncover and modify surface magnetic properties. Combining in-situ molecular beam epitaxy and state-of-the-art spin-polarized scanning tunneling microscopy (SP-STM) techniques, we investigate spin-polarization change in ferromagnetic (FM) Co nanoislands and single molecules. The confined free-electron-like s-p states on the Co islands surface form interference patterns, and result in spatial variations of electron and spin-polarization distributions, which can be adjusted by island sizes and bias energies.
Depositing organic molecules on the Co islands, we discover intriguing organic-FM interfacial properties, which have been proved crucial in organic spintronics. While manganese phthalocyanine (MnPc) follows the Co spin-polarization near the Fermi level, pentacene (C22H14, PEN) exhibits an opposite one. Ab initio calculations show that the key factor is the orbital hybridizing with Co. Different from Mn d orbitals hybridizing with Co d states, PEN molecules form p-d hybridizations with Co. In addition, the spin-dependent bonding and antibonding states in the p-d hybridizations make the PEN symmetry spin-dependent. In SP-STM images, PEN molecules are found bent or unperturbed, depending on the island magnetization orientations. The results shows that well-chosen molecule types help to predict and design spin-polarization in organic spintronics in both energies and space.

Keywords: spin-polarized scanning tunneling microscopy, organic molecule, quasiparticle interference