1. Magnetoresistance in oxydized Ni nanocontacts Department of Applied Physics, U. Alicante, 03690 SPAIN D. Jacob, J. Fernández-Rossier, J. J. Palacios www.ua.es/personal/jfrossier/ V22.00002 Ni Oxygen Large Magnetoresistance >90% Small Magnetoresistance Ni A single atom can make a difference D. Jacob, JFR, J. J. Palacios PRB 71, R220403 (2005) D. Jacob, JFR, J. J. Palacios Cond-mat, 0603359

2. Motivation I: MR K. Bolotin et al. Nano Lett., 6 (1), 123, (06) EXPERIMENT: Small BMR in Ni 80 Fe 20 THEORY: Small BMR in PURE Ni nanocontacts D. Jacob, JFR; J. J. Palacios PRB71, R220403 (2005)

3. Bulk NiO=AF Mott Insulator Ni Oxigen Motivation II: Motivation III: Probing Ni-O-Ni chemical bond

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

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

6. Electronic Structure: Infinite chains FERROMAGNETIC HALF METAL Doubly degenerate E 1 band 2 B3LYP, NiO FM chain CRYSTAL03 Ni (+) O (-)

7. Electronic Structure: Infinite chains ANTIFERROMAGNETIC INSULATING CRYSTAL03 B3LYP, NiO AF chain Ni (+) O (-)

8. Electronic structure: nanocontact Infinite system without translational invariance Cluster Embedded calculation Cluster in DFT aprox, LCAO, GAUSSIAN03 Leads: semiempirical TB, Bethe lattice  Ni Oxigen 

9. Nanocontacts: Single Oxygen Bridge High MR

10. Electronic Structure: Infinite chains FERROMAGNETIC INSULATING WARNING: Small MR

11. Ni SINGLE ATOM SPIN VALVE Ni Conducting Insulating

12. 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