Noncollinear exchange coupling in a trilayer magnetic junction and its connection to Fermi surface topology

We investigate the noncollinear exchange coupling across a trilayer magnetic junction composed of an intermediate layer with Rashba interaction and two sandwiching ferromagnetic layers. To compute the mediated exchange coupling, one needs to go beyond the single-particle argument and integrate over the contributions from the whole Fermi surface. Surprisingly, we find that the topology of the Fermi surface plays a crucial role in determining whether the oscillatory Ruderman-Kittel-Kasuya-Yosida or the spiral interactions will dominate. At the end, we discuss the connection of our numerical results to experiments and potential applications.