Berlin 2005 – wissenschaftliches Programm
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MA: Magnetismus
MA 20: Poster:Schichten(1-29),Spintrsp(30-45),Ex-Bias(46-63),Spindyn(64-75),Mikromat.(76-80),Cluster(81-94),Abbv.(95-99),Obflm(100-02),SpElek.(103-09),E-Theo(110-14),Mikromag.(115-16),Spin+PÜ(117-26),Mag.Mat.(127-51),Meth.(152-55),Mol.Mag(156-59),Kondo(160-65
MA 20.44: Poster
Montag, 7. März 2005, 14:00–18:00, Poster TU C
Tunneling magnetoresistance of CnHm (n=1,2,6, m=2,4,6) molecules sitting between Co clusters — •H. Zare Kolsaraki and H. Micklitz — II. Physikalisches Institut, Universität zu Köln,Zülpicher Str. 77, D-50937, Köln, Grmany
Spin-dependent transport in artificially nano-structured materials composed of magnetic clusters separated by insulating molecules is an actual field of research. Films composed of in-beam prepared Co clusters (mean diameter ≃ 4.5 nm) and various hydrocarbon molecules CnHm (n=1,2,6, m=2,4,6) have been prepared by co-deposition onto a cold (T ≃ 35 K) substrate. The temperature dependence of the resistivity ρ for all films shows the excepted lnρ ∝ T−1/2 behavior, typical for variable range tunneling. The tunneling magnetoresistance (TMR) is independent of the cluster volume fraction vcl in Co/CH4, Co/C2H2 and Co/C6H6, while TMR in Co/C2H4 strongly depends on vcl. TMR(T = 0) in Co/CH4 and Co/C2H4 (for largest vcl) is similar to that observed in non-interacting Co/Kr(Xe)-systems [TMR(0) ≃ 15%], while TMR(0) in Co/C2H2, Co/C6H6 and Co/C2H4 (for smallest vcl) is increased by a factor of about 2 [TMR(0) ≃ 30%]. We propose that the direct contact between Co-cluster surface-atoms and C-atoms is responsible for the enhanced TMR. The change of the TMR in C2H4 with changing vcl reflects the change in the orientation of the CnHm molecules sitting between two Co clusters: for large vcl one molecule sits with its C-C axis perpendicular to the cluster surface [small TMR(0)], while for small vcl two molecules are positioned with the C-C axis parallel to the cluster surface [large TMR(0)].