Permanent magnet comprising a stack of ferromagnetic and antiferromagnetic layers

A permanent magnet includes at least two antiferromagnetic layers and at least two first ferromagnetic layers. A magnetization direction of each first ferromagnetic layer is set, by an exchange coupling, with one of the antiferromagnetic layers of the stack, parallel to and in the same direction as the magnetization directions of the other first ferromagnetic layers. The permanent magnet also includes at least one second ferromagnetic layer. A magnetization direction of each second ferromagnetic layer is pinned only by RKKY (Ruderman-Kittel-Kasuya-Yosida) coupling with at least one of the first ferromagnetic layers or with at least one other of the second ferromagnetic layers.