PPB as a transport material for spintronic devises

Alexey A. Lachinov ,  Natalia V. Vorobjeva ,  Victor M. Kornilov 

Institute of Molecules and Crystal Physics, Ufa Scientific Centre of Russian Academy of Sciences, 151 Prospekt Oktyabrya, Ufa 450075, Russian Federation

Abstract

In this study the non-conjugated polyarylenephthalides class polymer are offered for applying it instead conventional conjugated polymers. Polymer is a poly(3,3’-phthalydiliden-4,4’biphenylen) (PPB). It is the non-conjugated polymer with wide band gap (~4eV). In other words it is insulator substance under normal conditions. But this polymer is able to change its conductive state from insulator to metal or vice versa. High conductive state can be reached in thin films. Thickness of the film should be less 1 μm. Sometimes it is necessary to apply any external fields. These fields are pressure, electric field, magnetic field, etc. High conductive polymer film has the following properties: specific resistance is 10-4 Ohm*cm; local current density is up to 106 A/cm2. Conductivity is the metallic type one. It is necessary to notice that film surface stays safe and isn’t damaged. There are different factors provides this interesting features of PAP-films. But the main are following. The absence of the electron-hole symmetry in these polymers is an important particularity of their electron structure. Quantum-chemical calculations showed that the electron states forming the highest occupied molecular orbital (HOMO) are localized on the molecule backbone. As well as the electron states corresponding to the lowest unoccupied molecular orbital (LUMO) are localized on the side fragment of the molecule. In connection with this fact one can propose the electron-hole excitation absence. So this will further spin coherent transport through the polymer film. Correspond to last fact it is promising to design spintronic devise based on polyarylenephthalides film. Giant magnetoresistance phenomenon was observed in ferromagnetic/polymer/metal structure. Nickel substrate was used as ferromagnetic layer which can inject spinpolarized charge carriers into PPB transport layer. Relative resistance changing was up to 10 orders of magnitude. Magnetic field required for switching didn’t exceed 200mT. GMR can be both positive and negative. It depends on the resistance of sample initial state. All measurements were realized at room temperature and in air atmosphere. Thus these advantages of GMR phenomenon in ferromagnetic/polymer structure are very useful for spintronic devices and its can be put into practice recently. This work is supported by fundamental investigation fund of PSD RAS “Physics of new materials and structures” and RFBR grant № 08-02-12042-ofi.

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Presentation: Oral at E-MRS Fall Meeting 2009, Symposium E, by Alexey A. Lachinov
See On-line Journal of E-MRS Fall Meeting 2009

Submitted: 2009-05-06 08:18
Revised:   2009-06-07 00:48
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