Quantum oscillations of properties in magnetic multilayers (invited)

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Abstract
An oscillatory interlayer exchange coupling observed in many sandwich and multilayer films can be understood as an interference effect of electron waves partially reflected at each interface with spin dependent reflection coefficients. Consequently, we might expect all magnetic properties in some way related to the density of states to oscillate as a function of the magnetic and nonmagnetic layer thickness. In order to experimentally test this concept we have measured different magnetic properties of Ni/Au multilayer films prepared by magnetron sputtering on glass substrates. The Ni thickness was kept constant at tNi=(7.3±0.5) Å while the Au layer thickness was varied between 4 Å and 80 Å. The films had a coherent fcc structure with (111) texture. The saturation field and the remanence oscillate as a function of tAu with a period which agrees well with a theoretical value calculated from the bulk Fermi surface of Au and proves that indeed an oscillatory exchange coupling is present. The Curie temperature shows oscillations with tAu clearly correlated with the exchange coupling constant, J: TC oscillates like the absolute value of J. This behavior is indeed expected from mean field theory. Similar oscillations are found for the spin wave parameter and the ground state magnetic moments. The variation of the exchange coupling with temperature and the role of inhomogeneities for the interpretation of the experimental data are discussed.