Neutron Scattering Study of Antiferromagnetic and Ferromagnetic Coupling in Ni/Ag Multilayers

Abstract

Indirect magnetic coupling in sputtered Ni/Ag multilayers has been recently studied by magnetization and magnetoresistance techniques. These experiments indicate that coupling is antiferromagnetic through 11 and 30 A of silver, and probably ferromagnetic through 20 Å. We present here direct evidence for such a magnetic coupling for all three thicknesses, as obtained from low angle neutron scattering experiments. Multilayers in which the Ag layer thickness is either 11 or 30 Å both exhibit a supplementary diffraction peak at a q value corresponding to twice the chemical period. Its evolution with both temperature and applied field confirms its purely magnetic origin. In order to study the coupling through 20 Å of silver, we prepared a multilayer in which the Ag layers are alternately 11 and 20 Å thick. In this case, we also observe a doubling of the chemical period. The coupling through 11 Å being antiferromagnetic, this unambiguously shows that the coupling through 20 Å is ferromagnetic.