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

Motivated by recent experiments, the effect of the interlayer exchange interaction J(inter) on the magnetic properties of coupled Co/Cu/Ni trilayers is 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. For an increasing J(inter) the resonancelike peak of the longitudinal Ni susceptibility is shifted to larger temperatures, whereas its maximum value decreases strongly. A decreasing Ni film thickness enhances the induced Ni magnetization for T greater than or similar to T-C,T-Ni. The measurements cannot 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 Hamiltonian and a Green's-function approach. [S0163-1829(99)51446-X].