Magnetic ground state and Fermi surface of bcc Eu

Using spin-spiral technique within the full potential linearized augmented-plane-waves (LAPW) electronic structure method, we investigate the magnon spectrum and N\'eel temperature of bcc Eu. Ground state corresponding to an incommensurate spin spiral is obtained in agreement with experiment and previous calculations. We demonstrate that the magnetic coupling is primarily through the intra-atomic f-s and f-d exchange and Ruderman-Kittel-Kasuya-Yosida mechanism. We show that the existence of this spin spiral is closely connected to a nesting feature of the Fermi surface, which was not noticed before.