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Science 1 October 2004:
Vol. 306. no. 5693, pp. 86 - 89
DOI: 10.1126/science.1102068
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Reports

The Kondo Effect in the Presence of Ferromagnetism

Abhay N. Pasupathy,1 Radoslaw C. Bialczak,1 Jan Martinek,2 Jacob E. Grose,1 Luke A. K. Donev,1 Paul L. McEuen,1 Daniel C. Ralph1*

We measured Kondo-assisted tunneling via C60 molecules in contact with ferromagnetic nickel electrodes. Kondo correlations persisted despite the presence of ferromagnetism, but the Kondo peak in the differential conductance was split by an amount that decreased (even to zero) as the moments in the two electrodes were turned from parallel to antiparallel alignment. The splitting is too large to be explained by a local magnetic field. However, the voltage, temperature, and magnetic field dependence of the signals agree with predictions for an exchange splitting of the Kondo resonance. The Kondo effect leads to negative values of magnetoresistance, with magnitudes much larger than the Julliere estimate.

1 Laboratory of Atomic and Solid State Physics, Cornell University, Ithaca, NY 14853, USA.
2 Institut für Theoretische Festkörperphysik, Universität Karlsruhe, 76128 Karlsruhe, Germany; Institute for Materials Research, Tohoku University, Sendai 980–8577, Japan; and Institute of Molecular Physics, Polish Academy of Sciences, 60–179 Poznan, Poland.

* To whom correspondence should be addressed. E-mail: ralph{at}ccmr.cornell.edu

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