Magnetization and susceptibility of coupled ferromagnetic trilayers calculated with a Green's function type theory

The effect of the interlayer exchange interaction J(inter) in coupled Co/Cu /Ni trilayers is studied theoretically, as motivated by recent experiments. In these systems, J(inter) induces a considerable Ni magnetization for tem peratures above the Curie temperature T-C,T-Ni of the Ni film. We will show that this strong effect can only be understood if magnetic fluctuations in these 2D-like systems are taken into account. A mean field estimate, negle cting these fluctuations, yields a ten times smaller increase of the Ni mag netization. The induced magnetization increases for both a ferromagnetic (J (inter)> 0) and an antiferromagnetic (J(inter)< 0) interlayer coupling. The Ni susceptibility, exhibiting a resonance-like peak at T greater than or s imilar to T-C,T-Ni, looks different for these two cases. The calculations a re performed with the help of a Heisenberg Hamiltonian and a Green's functi on approach. (C) 2000 American Institute of Physics. [S0021-8979(00)88208-0 ].