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Engineering of Spin Injection and Spin Transport in Organic Spin Valves Using π‐Conjugated Polymer Brushes
Author(s) -
Geng Rugang,
Roy Anandi,
Zhao Wenbo,
Subedi Ram Chandra,
Li Xiaoguang,
Locklin Jason,
Nguyen Tho Duc
Publication year - 2016
Publication title -
advanced functional materials
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 6.069
H-Index - 322
eISSN - 1616-3028
pISSN - 1616-301X
DOI - 10.1002/adfm.201504201
Subject(s) - materials science , magnetoresistance , spin diffusion , brush , amorphous solid , conjugated system , covalent bond , electrode , spin (aerodynamics) , spin valve , polymer , diffusion , condensed matter physics , organic semiconductor , layer (electronics) , nanotechnology , polymer chemistry , composite material , optoelectronics , crystallography , ferromagnetism , organic chemistry , chemistry , magnetic field , thermodynamics , physics , quantum mechanics
Charge transport in amorphous organic semiconductors is governed by carriers hopping between localized states with small spin diffusion length. Furthermore, the interfacial resistance of organic spin valves (OSVs) is poorly controlled resulting in controversial reports of the magnetoresistance (MR) response. Here, surface‐initiated Kumada transfer polycondensation is used to covalently graft π‐conjugated poly(3‐methylthiophene) brushes from the La 0.67 Sr 0.33 MnO 3 (LSMO) bottom electrode. The covalent attachment along with the brush morphology allows control over the LSMO/brush interfacial resistance and large spacer mobility. Remarkably, with 15 nm brush spacer layer, an optimum MR effect of 70% at cryogenic temperatures and a MR of 2.7% at 280 K are observed. The temperature dependence of the MR is nearly an order of magnitude weaker than that found in control OSVs made from spin‐coated poly(3‐hexylthiophene). Using a variety of different brush layer thicknesses, the thickness‐dependent MR at 20 K is investigated. A spin diffusion length of 17 nm at −5 mV junction voltage rapidly increased to 48.4 nm at −260 mV.