Tunneling magnetoresistance of C2H2 molecules sandwiched between Co clusters

The tunneling magnetoresistance (TMR) of samples containing well-defined Co clusters (∼4.5 nm mean diameter) embedded in C2H2 matrices essentially is independent of Co-cluster volume fraction vCo and reveals a value of about 26% at T=2 K. This result is in contrast to that obtained for Co clusters embedded in C2H4 matrices (Phys. Rev. B 67 (2003) 094433). In the latter system the TMR strongly decreased with increasing vCo indicating different possible orientation of the C2H4 molecule sandwiched between the Co clusters. We, therefore, conclude that the C2H2 molecules are sandwiched in a rather well-defined orientation between the Co clusters. They probably form double layers of C2H2 molecules with the C-C bond axis parallel to the Co cluster surface