Indirect exchange spring between FePt and Fe with a Ru interlayer

Indirect exchange spring in magnetron-sputtered FePt/Ru/Fe trilayers as well as multilayers have been investigated. Interlayer exchange coupling between FePt and Fe layers through a Ru spacer was obtained with an oscillation period of about 1 nm. Magnetic properties of FePt thin films with different nominal thicknesses deposited on MgO (1 1 0) substrates at 400 °C showed that 12.5 nm thick FePt film had both high coercivity and good squareness. In FePt/Ru/Fe trilayers, ferromagnetic coupling between the two magnetic layers was achieved with a 0.5 nm thick Ru layer, and the saturated magnetization was largely improved after using interlayer exchange coupling with Fe while the coercivity changed little, which indicated that indirect exchange spring was a promising approach for high-performance magnets. Multilayers with such structures had also been studied with different thickness ratio of the two magnetic layers and strong exchange coupling was achieved as Fe thickness ratio increased.