Tunneling magnetoresistance of Co clusters in MgF2

Abstract

Samples of Co clusters embedded in a MgF2 matrix have been prepared by the codeposition of well-defined Co clusters (mean diameter L≃4.5 nm) and MgF2 molecules onto a cold substrate. This system shows a temperature-dependent tunneling magnetoresistance (TMR) which has a value of 34.7(2)% at 2.5 K, the largest TMR value reported for a granular Co system. This large TMR value either is due to an antiferromagnetic coupling of those Co clusters between which the tunneling occurs or is caused by an enhanced spin-polarization of the tunneling electrons. The latter may be caused by a cluster–surface/matrix interaction leading to dominated d-electron tunneling due to Co(3d)–F(2p) hybridization.