Tunneling magnetoresistance between Co clusters coated with CO molecules

Abstract

Films made of in-beam prepared Co clusters (mean diameter $\ensuremath{\approx}4.5\mathrm{nm})$ coated with CO molecules show an unusual large tunneling magnetoresistance (TMR) of about 50% at $T=1.7\mathrm{K}.$ Using a model for the T-dependence of the TMR which includes T-dependent spin disorder at the cluster surface and higher-order tunneling processes below 4 K we obtain a spin polarization P of the tunneling electrons of $|P|=0.80(3).$ Such a high $|P|$ value can be explained by an interaction between the Co cluster surface atoms and the CO molecules which leads to preferred d-electron tunneling. An increased spin polarization of the d-electrons due to a charge transfer process from the CO molecule to the Co atom may be an additional reason for the unusual large TMR.