Giant magnetoresistance of Co Au multilayer point contacts

We have measured the giant magnetoresistance (GMR) of granular Co/Au point contacts, fabricated by deposition of [Co(0.3 nm)/Au(4 nm)](10) multilayers with molecular beam epitaxy. Two Co deposition rates were used to obtain t wo types of contacts with different Co cluster size. The measured GMR ratio s are in the range 5-12%. These GMRs come from the constriction region, sin ce the current in-plane contribution of the multilayer was shorted by a thi ck Au cap. GMR curves characteristic of both superparamagnetic and ferromag netic Co clusters were observed for either contact type. Device-to-device d ifferences in the GMR ratio and in the magnetic behaviour, and sudden jumps in the GMR indicate that only a few Co clusters in the constriction genera te the GMR. (C) 1999 Elsevier Science B.V. All rights reserved.