Strongly enhanced tunneling magnetoresistance in granular films of Co clusters in a CO ₂ matrix: Evidence for a cluster-surface/matrix interaction

Abstract

A new granular system, namely, Co clusters embedded in solid CO2, has been prepared by the co-deposition of well-defined Co clusters (mean diameter L ≃ 4.2 nm, and CO2 molecules onto a cold substrate. This system shows a temperature-dependent tunneling magnetoresistance (TMR) which has a value of 31(2)% at 2.5 K. Using Jullière's model this value corresponds to a spin-polarisation |P| = 0.68(2) of the tunneling electrons, compared to P = 0.42 for granular Co/Xe(Kr) or planar Co/Al2O3/Co. We interpret this enhancement of P as caused by a cluster-surface/matrix interaction.