Enhanced induced magnetization in coupled magnetic trilayers in the presence of spin fluctuations

Motivated by recent experiments, the effect of the interlayer exchange inte raction J(inter) on the magnetic properties of coupled Co/Cu/Ni trilayers i s studied theoretically. Here the Ni film has a lower Curie temperature T-C ,T-Ni than the Co film in case of decoupled layers. We show that by taking into account magnetic fluctuations the interlayer coupling induces a strong magnetization for T greater than or similar to T-C,T-Ni in the Ni film. Fo r an increasing J(inter) the resonancelike peak of the longitudinal Ni susc eptibility is shifted to larger temperatures, whereas its maximum value dec reases strongly. A decreasing Ni film thickness enhances the induced Ni mag netization for T greater than or similar to T-C,T-Ni. The measurements cann ot be explained properly by a mean-field estimate, which yields a ten times smaller effect. Thus, the observed magnetic properties indicate the strong effect of two-dimensional magnetic fluctuations in these layered magnetic systems. The calculations are performed with the help of a Heisenberg Hamil tonian and a Green's-function approach. [S0163-1829(99)51446-X].