The role of heavy metal ions on spin transport in organic semiconductors

It is generally believed that spin-orbit coupling (SOC) strength and the associated spin relaxation can be enhanced by introducing heavy metal ions in organic semiconductors. Here, we systematically study the spin transport in two organic semiconductors, tris(2-phenylpyridine)iridium (Ir(ppy)3) and...

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Bibliographic Details
Published in:New journal of physics 2015-01, Vol.17 (1), p.13004-9
Main Authors: Chen, B B, Wang, S, Jiang, S W, Yu, Z G, Wan, X G, Ding, H F, Wu, D
Format: Article
Language:English
Subjects:
Aluminum
Carrier mobility
Diffusion length
Electron states
Excitons
Heavy metals
Hydroxyquinoline
Infrared spectroscopy
Ligands
Magnetoresistance
Magnetoresistivity
Metal ions
Orbitals
Organic chemistry
Organic semiconductors
organic spintronics
Photoluminescence
Physics
Relaxation time
Semiconductors
Spectroscopy
Spectrum analysis
spin orbit coupling
spin relaxation
Spin valves
Spin-orbit interactions
Strength
Transport
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Summary:It is generally believed that spin-orbit coupling (SOC) strength and the associated spin relaxation can be enhanced by introducing heavy metal ions in organic semiconductors. Here, we systematically study the spin transport in two organic semiconductors, tris(2-phenylpyridine)iridium (Ir(ppy)3) and tris-(8-hydroxyquinoline) aluminum (Alq3), which have similar chemical structures except that Ir(ppy)3 contains a heavy metal ion Ir. As expected, the photoluminescence spectroscopy measurements show that the SOC strength in Ir(ppy)3 is several orders of magnitude larger than in Alq3. Surprisingly, the spin diffusion length in Ir(ppy)3, deduced from magnetoresistance measurements in Ir(ppy)3-based organic spin valves, is longer than in Alq3. Considering the lower carrier mobility in Ir(ppy)3, the spin relaxation time in Ir(ppy)3 is much longer than in Alq3, implying that the SOC strength in Ir(ppy)3 is weaker than in Alq3. The seemingly contradictory results of photoluminescence spectroscopy and magneto-transport can be explained by the SOC strength depending on the electronic states of a material. The weak SOC strength in Ir(ppy)3 observed in magneto-transport measurements is due to the strong ligand field induced orbital moment quenching for Ir3+ and the polarons transporting in the ligands. However, the excitons involved in photoluminescence spectroscopy overlap with the Ir ion and transforms Ir3+ to Ir4+, which has non-zero spin and orbital moments and hence results in high SOC strength.
ISSN:1367-2630
1367-2630
DOI:10.1088/1367-2630/17/1/013004