Berlin 2005 – wissenschaftliches Programm

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TT: Tiefe Temperaturen

TT 8: Posters Transport

TT 8.19: Poster

Freitag, 4. März 2005, 14:00–18:00, Poster TU C

Conductance Measurements on Ferromagnetic Breakjunctions — •Cécile Bacca, Magdalena Hüfner, H.-F. Pernau, and Elke Scheer — Fachbereich Physik, Universität Konstanz

We investigate lithographically fabricated breakjunctions of ferromagnetic metals. With the help of a three-point bending mechanism, the bridges can be opened to a single-atom contact, broken to a vacuum-tunnel contact and closed again repeatedly at low temperatures (T≤ 4.2K). We observe steps in the conductance that are due to atomic rearrangements in the contact region [1] and calculate the preferred conductance value of a single Co atom with and without magnetic field. In addition we observe very high magnetoconductance effects up to 150% for single-atom or 500% for tunnel contacts in magnetic fields up to 5 T and perpendicular to the sample plane. However, the details of the magnetoconductance curves are not yet fully understood. In order to separate the contributions of the different possible effects (magnetostriction, TMR, BMR, AMR,...) we analyse the magnetoconductance as a function of the symmetry of the contact, of the free-standing bridge length, and for different materials (Co, Ni). In parallel we calculate [2] the magnetization state as a function of the geometry of the contact, the film thickness and its magnetic history. [1] J.M. Krans et al. Nature 375, 767 (1995)

[2] M.J. Donahue and D.J. Porter, OOMMF’s User Guide (see http://math.nist.gov/oommf)