Influence of the nature of the buffer on the coupling and the transport properties in Co/Ru/Co sandwiches

A series of Co-30 Angstrom/Ru-5 Angstrom/Co-30 Angstrom sandwiches has been prepared by ion beam sputtering on a glass substrate using different buffe r layers in order to optimize the antiferromagnetic (AF) coupling strength and the giant magnetoresistance (GMR) signal. The best GMR of about 1.7% is obtained for a Co/Ru/Co sandwich deposited on the Fe-50 Angstrom/Co-5 Angs trom/Cu-30 Angstrom buffer. On the basis of the GMR and exchange coupling r esults, the two more interesting buffers have been chosen for a detailed an alysis. Two additional series have been grown with varying Ru spacer layer thickness on these two buffers: 150 Angstrom Ru and Fe-50 Angstrom/Co-5 Ang strom/Cu-30 Angstrom buffer layers. For the two series, oscillations in mag netoresistance and AF indirect exchange coupling have been observed as a fu nction of the Ru thickness with the same period of about 10 Angstrom. The f irst AF peak is observed at a thickness of 6 Angstrom Ru for the series gro wn on Ru-150 Angstrom buffer and 4 Angstrom for the series grown on a Fe-50 Angstrom/Co-5 Angstrom/Cu-30 Angstrom buffer layer. At this first peak, bo th GMR and AF coupling are largely enhanced with values J(AF)=-2.6 erg/cm(2 ) and a GMR of 1.34% for the Fe-50 Angstrom/Co-5 Angstrom/Cu-30 Angstrom bu ffer compared to J(AF)=-0.75 erg/cm(2) and a GMR of 0.08% for the Ru-150 An gstrom buffer. Atomic force microscopy and x-ray diffraction studies have a lso been performed in order to understand the origin of the observed increa se in GMR and AF exchange coupling between the two series. (C) 2000 America n Institute of Physics. [S0021- 8979(00)04915-X].