TY - JOUR
T1 - Tunneling anisotropic magnetoresistance in C60-based organic spintronic systems
AU - Wang, K.
AU - Sanderink, J.G.M.
AU - Bolhuis, T.
AU - van der Wiel, W.G.
AU - de Jong, M.P.
N1 - eemcs-eprint-25380
PY - 2014/5/16
Y1 - 2014/5/16
N2 - C 60 fullerenes are interesting molecular semiconductors for spintronics since they exhibit weak spin-orbit and hyperfine interactions, which is a prerequisite for long spin lifetimes. We report spin-polarized transport in spin-valve-like structures containing ultrathin (<10 nm) C 60 layers, ferromagnetic (FM) epitaxial face-centered-cubic (fcc) Co (111) contacts, AlO x tunnel barriers, and nonmagnetic Al counter electrodes. Even though genuine spin-valve behavior cannot occur for only one FM contact, we find significant tunneling anisotropic magnetoresistance (TAMR) upon rotating the in-plane magnetization, originating from spin-orbit interaction (SOI) induced anisotropy of the fcc (111) Co bands. The uniaxial magnetocrystalline anisotropy of the Co electrodes results in a predominantly twofold symmetric in-plane TAMR effect. We investigated the TAMR effect in the direct tunneling regime (2 nm C 60 ), at the transition point to two-step tunneling (4 nm C 60 ), and in the multistep regime (8 nm C 60 ). A sizable TAMR of 4.5% is found at 5 K under application of a 500-mT in-plane magnetic field for C 60 layers of 2 nm, which is strongly suppressed at 8 nm thickness, indicating that TAMR may strongly contribute to the “spin-valve‿ signal for direct tunneling, but not for multistep tunneling. The TAMR effect is proposed to be due to a combination of SOI induced modulation of the tunneling DOS upon rotating the in-plane magnetization of the fcc epitaxial Co thin film, resonant tunneling processes involving interfacial states, and different Bychkov-Rashba SOI at the different interfaces.
AB - C 60 fullerenes are interesting molecular semiconductors for spintronics since they exhibit weak spin-orbit and hyperfine interactions, which is a prerequisite for long spin lifetimes. We report spin-polarized transport in spin-valve-like structures containing ultrathin (<10 nm) C 60 layers, ferromagnetic (FM) epitaxial face-centered-cubic (fcc) Co (111) contacts, AlO x tunnel barriers, and nonmagnetic Al counter electrodes. Even though genuine spin-valve behavior cannot occur for only one FM contact, we find significant tunneling anisotropic magnetoresistance (TAMR) upon rotating the in-plane magnetization, originating from spin-orbit interaction (SOI) induced anisotropy of the fcc (111) Co bands. The uniaxial magnetocrystalline anisotropy of the Co electrodes results in a predominantly twofold symmetric in-plane TAMR effect. We investigated the TAMR effect in the direct tunneling regime (2 nm C 60 ), at the transition point to two-step tunneling (4 nm C 60 ), and in the multistep regime (8 nm C 60 ). A sizable TAMR of 4.5% is found at 5 K under application of a 500-mT in-plane magnetic field for C 60 layers of 2 nm, which is strongly suppressed at 8 nm thickness, indicating that TAMR may strongly contribute to the “spin-valve‿ signal for direct tunneling, but not for multistep tunneling. The TAMR effect is proposed to be due to a combination of SOI induced modulation of the tunneling DOS upon rotating the in-plane magnetization of the fcc epitaxial Co thin film, resonant tunneling processes involving interfacial states, and different Bychkov-Rashba SOI at the different interfaces.
U2 - 10.1103/PhysRevB.89.174419
DO - 10.1103/PhysRevB.89.174419
M3 - Article
SN - 1098-0121
VL - 89
SP - 174419
JO - Physical review B: Condensed matter and materials physics
JF - Physical review B: Condensed matter and materials physics
IS - 17
ER -