Organic Spintronics with phthalocyanines as model systems

Transcription

1 Organic Spintronics with phthalocyanines as model systems S. Boukari

2 Teams involved : P. Seneor, UMP CNRS/Thales : nanoindentation M. Alouani, IPCMS : calculations E. Beaurepaire, IPCMS : fabrication, spectroscopy

3 Outline Organic spintronics: generalities Magnetoransport with Co-phthalocyanines Interaction between Mn-phthalocyanines and metallic surfaces

4 Organic Spintronics: generalities

5 Why organic electronics? Technological: making devices by simple techniques on flexible substrates of large size New properties and multi-functionality: benefit of a range of extremely broad materials

6 Organic spintronics Definition: spin-dependent transport in organic materials. Purpose: translate what is being done with inorganic materials to profit from the potentiality of organic materials

7 Spintronics Magnetoresistance: resistance depends on the magnetic state of the device é é A V Resistance A V V R = I p R ap Applied mag. field MR = R ap R p R p

8 Tunneling effect: insulating spacer. P = N N max max + N N min min P = N N maj maj N + N min min 2 2P MR = P MR is large if P is large

9 Diffusion : metallic or SC Spacer. MR = 2 P 1 P 2 L 1+ 1 τ n τ sf τ n = Time of residence of the é in the spacer τ n L v T v = velocity of the é T = transmission coeff. A é V τ sf = Lifetime of the spins We want τ τ n sf L v T τ sf small

10 Organic and spintronics? We want τ τ n sf L v T τ sf small v τ sf T metals high weak. ~1 Inorganic Semicond. medium to high high weak. Organic Semicond. medium high weak.

11 Magnetoransport with Cophthalocyanines

12 The phthalocyanines M=H 2, Mn, Fe, Co Commercial Availability Can be evaporated

13 Fabrication of devices Resist CoPc~2-3 nm AFM Tip Co(~10 nm) Si Junction 1-10 nm 2 OMBE Metal MBE I(V) Si

14 Mesurement of magnetoresistance Co/CoPc (2-3 nm)/co/coo 2K MR negative, coercive field = f(v) j~ A/cm 2

15 Mesurement of magnetoresistance 2K High merit factor : voltage such that MR = MR(V 2 = 0)

16 Possible model Resonant tunneling: explain the negative MR P(%) MR=-P 2 ~-18% for Co, To compare with measured -27%<MR<-23% Fe 45 Co 42 Ni 33 Co 50 Fe To be developed for quantitative and explain the merit factor

17 Conclusions regarding transport Evidence of MR through organic spacer Negative MR High merit factor Model: resonant tunneling Perspective: multifunctional organic spintronics device

18 Interaction between Mn-Pc and metallic surfaces

19 XAS and XMCD on Mn-Pc/Cu and Mn-Pc/Co Learn about electronic and magnetic properties to support a transport model Mn-Pc : element specific measurements on Mn and Co

20 XAS (Arb. Units) MnPc(1ML)/Cu MnPc(2.5ML)/Cu MnPc(1ML)/Co MnPc(2.3ML)/Co Nitrogen K edge Photon Energy (ev) Influence of Cu and Co on Mn-Pc is different

21 Magnetic dichroism at the Mn and Co L-edge 1.04 (a) 1.02 XAS (Arb. Units) XMCD ML MnPc 0.5 ML MnPc MnPc/Cu Energy (ev) (c) XMCD (d) XMCD MnPc/Cu H (T) 2 1 MnPc/Co H (T) 1.02 (b) XAS (Arb. Units) XMCD MnPc/Co Energy (ev) Mn-Pc ferromagnetically coupled with Co

22 E-E min (Ry) Emax - E (Ry) fcc Co(001) fcc Cu(001) MnPc Distance to Surface (A) Mn-Pc is chemisorbed on Co, physisorbed on Cu

23 Magnetic moments : Mn Co, N

24 Conclusion regarding interaction with surfaces : Weak interaction with Cu Strong interaction with Co Magnetic coupling with Co at RT

25 Perspectives : Calculations : transport with Co-Pc and Mn-Pc Experiments : transport with Mn-Pc