Increase in Period Of Oscillatory Coupling in Cu by Doping with Ni
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INCREASE IN PERIOD OF OSCILLATORY COUPLING IN Cu BY DOPING WITH Ni S.S.P. PARKIN, C. CHAPPERTt and F. HERMAN IBM Research Division, Almaden Research Center, 650 Harry Road, San Jose, CA 95120-6099. tlnstitut d'Flectronique Fondamentale, Universite Pnris-Sud, Orsay, France.
ABSTRACT The origin of oscillatory interlayer coupling via Cu is explored in sputtered Co/Cu multilayers by varying the hole concentration in the copper layers by doping with elements of different valence. Detailed studies were carried out for a series of Cu-Ni alloys. The oscillation period of pure Cu is observed to increase monotonically with increasing Ni concentration and is almo-t doubled for 40 atomic % Ni. The increa.e in oscillation period can be accounted for by considering changes in the topology of the Fermi surface of the alloy resulting from the change in band filling. INTRODUCTION The detailed origin of the magnetic coupling of thin magnetic layers via intervening thin metallic spacer layers is a subject of considerable interest[I-9]. For many transition and noble metal spacer layers the magnetic exchange coupling is found to oscillate back and forth between ferromagnetic and antiferromagnetic coupling as the spacer layer thickness is increased[2-4]. Whether or not the coupling can be accounted for within the well known Ruderman-Kittel-Kasuya-Yosida (RKKY) model[l0, II] is a subject of considerable debate. In RKKY models the oscillation period is related to the inverse mngnitude of wavevectors along the multilayer direction connecting states at the Fermi surface with antiparallel Fermi velocities. Certain experimental results are difficult to reconcile within simple RKKY models. Firstly a common oscillation period of -8 to 12A[4] is observed in most metals with the exception oi Cr[2, 5-7] even though the topology of the Fermi surface varies considerably from metal to metal. Secondly the interlayer coupling ,strength is found to increase systematically with d band filling of the spacer layer metal for the 3d, 4d and 5d transition metals[4], although within RKKY treatments the strength of the coupling is also expected to depend on the detailed Fermi ýurface topology. Theoretical predictions of the oscillation period and coupling strength along principle crystallographic axes, based on experimentally determined bulk Fermi surfaces, haNe been carried out for the noble metals, Cu, Ag and Au within a simple RKKY treatmena[12, 13]. Such predictions can be tested by examining the oscillation period and coupling strength along different crystallographic orientations of multilayers containing these metals. This requires the growth of single crystal or highly oriented multilayers along several different crystal axes. Cu is the only spacer layer for which the orientation dependence of the coupling has been studied in detail. The coupling has been measured in experiments on crystalline Fe/Cu arnd Co/Cu multilayers oriented along [1001[9, 14, 15] and [110][16]. Similar long oscillation periods of
Mat. Res. Soc. Symp. Proc. Vol. 313. ©1993 Mater
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