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Single electron Transport in diluted magnetic semiconductor

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					Magnetoresistance in oxydized Ni nanocontacts
        D. Jacob, J. Fernández-Rossier, J. J. Palacios
           Department of Applied Physics, U. Alicante, 03690 SPAIN


                                                  Ni        Ni
          Ni Ni

                                                    Oxygen

       Small                            Large Magnetoresistance
  Magnetoresistance                             >90%
  D. Jacob, JFR, J. J. Palacios         D. Jacob, JFR, J. J. Palacios
   PRB 71, R220403 (2005)                   Cond-mat, 0603359

               A single atom can make a difference

                    www.ua.es/personal/jfrossier/            V22.00002
                             Motivation I: MR




       EXPERIMENT:
  Small BMR in Ni80Fe20
K. Bolotin et al. Nano Lett., 6 (1), 123, (06)

      D. Jacob, JFR; J. J. Palacios
          PRB71, R220403 (2005)

     THEORY: Small BMR in
     PURE Ni nanocontacts
 Motivation II:




Motivation III:
                               Ni    Ni



                                 Oxigen


                   Probing Ni-O-Ni chemical bond

                  Bulk NiO=AF Mott Insulator
         Electronic Structure calculation

    Ni       Ni
                                        2
                                 e
                              G
                                 h
                                             T (E
                                            n
                                                n    F   )
    Oxygen

                   Tight Binding                    B3LYP
Free Bands
                  •Parametrization 3D           Bulk NiO:
                  •Charge neutrality            • AF OK
                                                • Insulator OK
                        LDA                     •GAP Ok
                   •NiO: FM, no                 •Magnetic Moment
                   gap, no Mott                 OK
                   Hubbard                      •No Self
                   •Self Interaction            Interaction: OK
         Electronic Structure calculation

    Ni       Ni
                                              2
                                           e
                                        G
                                           h
                                                   T (E
                                                  n
                                                      n    F   )
      Oxigen

                   Tight Binding          B3LYP
Free Bands
                  •Parametrization 3D   Bulk NiO:
                  •Charge neutrality    • AF OK
                                        • Insulator OK
                        LDA             •GAP Ok
                   •NiO: FM, no         •Magnetic Moment
                   gap, no Mott         OK
                   Hubbard              •No Self
                   •Self Interaction    Interaction: OK
Electronic Structure: Infinite chains
 CRYSTAL03


 B3LYP, NiO FM chain
                            FERROMAGNETIC
                            HALF METAL
         2             Doubly degenerate E1 band




                               Ni(+)O(-)
Electronic Structure: Infinite chains
 CRYSTAL03



 B3LYP, NiO AF chain
                       ANTIFERROMAGNETIC
                       INSULATING

                            Ni(+)O(-)
Electronic structure: nanocontact

                            Ni   Ni

                                          
                             Oxigen


      •Infinite system without translational invariance
      •Cluster Embedded calculation
      •Cluster in DFT aprox, LCAO, GAUSSIAN03
      •Leads: semiempirical TB, Bethe lattice


G( E ) 
                1
                                 T ( E )  GG
           E  H  ( E )
  Nanocontacts: Single Oxygen Bridge


                       2e 2
                  GP 
High                    h
                                            2e 2
                                GDW    0.1
 MR                                          h



GP
     10
GDW
Electronic Structure: Infinite chains




                        FERROMAGNETIC
                          INSULATING


                           WARNING:
                           Small MR
SINGLE ATOM SPIN VALVE
       Ni               Ni




             GP
                  10
             GDW




     Ni

Conducting                   Insulating
          Conclusions
• A single atom can make a difference: Ni-O-Ni
  can have large MR
• A single atom can makes a difference:
  SINGLE ATOM SPIN VALVE
• Atomic sized contacts: PROBING TM-O-TM
  chemical bonding



          www.ua.es/personal/jfrossier

              Jfrossier@ua.es

				
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posted:10/8/2012
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