Inverse Magnetoresistance in Polymer Spin Valves

Area of Science:

• Organic electronics
• Spintronics
• Materials science

Background:

• Organic spin valves (OSVs) offer potential for novel electronic devices.
• Controlling magnetoresistance (MR) in OSVs is key for device applications.
• Regioregular poly(3-hexylthiophene) (RR-P3HT) is a promising organic semiconductor.

Purpose of the Study:

• Investigate the origin of both negative and positive magnetoresistance (MR) in organic spin valves (OSVs).
• Elucidate the mechanism behind the MR sign inversion in La_2/3Sr_1/3MnO₃/P3HT/AlO_x/Co devices.
• Propose a model to explain the observed magnetoresistance phenomena.

Main Methods:

• Fabrication of ferromagnetic La_2/3Sr_1/3MnO₃ (LSMO) electrodes using DC facing-target magnetron sputtering.
• Construction and characterization of vertical OSVs with RR-P3HT and AlO_x/Co electrodes.
• Detailed magnetoresistance measurements on devices with varying Co penetration and thicknesses.
• Utilized density functional theory (DFT) calculations for theoretical validation.

Main Results:

• Observed both negative MR (0.2%) in devices with Co penetration and positive MR (15.6%) in well-defined devices.
• MR measurements on LSMO/AlO_x/Co and LSMO/Co junctions excluded interference from insulating layers and individual ferromagnetic electrodes.
• A spin-dependent hybrid-interface-state model, considering Co penetration, successfully explained the MR sign inversion.

Conclusions:

• The study successfully demonstrated and explained the MR sign inversion in RR-P3HT based OSVs.
• The proposed model provides insights into controlling interfacial properties for novel OSV design.
• These findings contribute to the advancement of organic spintronic devices.