Organic semiconductors for spintronic applications: key factors for the improvement  of vertical hybrid devices

Ilaria Bergenti 1Valentin A. Dediu 1Alberto Riminucci 1Patrizio Graziosi 1Mirko Prezioso 1Francesco Borgatti 1Francesca Casoli 2Donald MacLaren 3John Chapman 3

1. Istituto per lo Studio dei Materiali Nanostrutturati (ISMN-CNR), Gobetti 101, Bologna 40129, Italy
2. IMEM- CNR (IMEM), Parma, Italy
3. University of Glasgow, Department of Physics and Astronomy, Glasgow, United Kingdom


π-conjugated organic semiconductors have emerged as suitable candidates in spintronic devices mainly thanks to their low spin orbit interaction. One of the most reproduced effects in organic spintronics is the  inverse magnetoresistive  effect in vertical Spin Valves (SV) based on archetypal organic materials Alq3 and containing half metallic manganite (LSMO) as bottom electrode and Cobalt as the top one. LSMO/Alq3 and Alq3/Co interfaces play a key role in the spin injection process; the occurrence of perturbing effects such as intermixing, chemical reactions, formation of dipole layers or molecular disruption  affects both charge and spin injection and thus the device performance.

Reproducible room temperature operation has been attained  on Alq3 based SV  trough the insertion of thin insulating tunnel barriers (usually 1-2 nm of Al2O3 or LiF)  at the  Alq3/Co interface.

We present a detailed investigation of LSMO and Co ferromagnetic films and their interfaces with Alq3 in presence of buffer insulating layer and we correlate the results with the operation of spin valve device.

In particular, structural information obtained from X-ray reflectivity measurements and High resolution TEM indicates that the presence of the tunnel barrier layer limits the Alq3/Co intermixing. The chemical states at the interfaces has been investigated by High Energy Photoemission Spectroscopy (HAXPES): the insertion of the tunnel barrier reduces the Co-Alq3 interaction, preventing very efficiently changes of the molecular electronic structure within the intermixed region.

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Presentation: Invited oral at E-MRS Fall Meeting 2009, Symposium E, by Ilaria Bergenti
See On-line Journal of E-MRS Fall Meeting 2009

Submitted: 2009-05-25 22:44
Revised:   2009-06-07 00:48
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