Dresden 2011 – wissenschaftliches Programm

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MA: Fachverband Magnetismus

MA 46: Magnetic Thin Films II

MA 46.2: Vortrag

Mittwoch, 16. März 2011, 17:15–17:30, CHE 184

Charge-induced reversible change of magnetic properties in ultrathin FePt films — •Karin Leistner, Norman Lange, Steffen Oswald, Sebastian Fähler, and Ludwig Schultz — IFW Dresden, PF 270116, 01171 Dresden

FePt has attracted a lot of interest as hard magnetic material due its high magnetocrystalline anisotropy. For various applications fast and reversible changes of magnetic properties induced by an electric field would be ideal. Weisheit et al. [Science 315 (2007) 349] showed that the coercivity of ultrathin FePt films can be changed by 4 % by electronic charging. Larger E-field induced effects are expected at critical points. We study continuous 2 nm thin FePt(001) films where perpendicular magnetocrystalline anisotropy competes with shape anisotropy. The films are charged in an electrolyte by applying an electric voltage of 2 to 3 V vs. Li/Li+. We observe a large reversible change of anisotropy (up to 20 %). At the same time, the magnitude of the anomalous Hall effect as a measure for the moment changes up to 4 %. XPS studies showed that the effect is strongly enhanced in films with a surface iron oxide layer, but smaller in films with low oxygen content. This implies that the moment increase at lower potentials results from electrochemical reduction of surface iron oxide species to metallic iron. The corresponding decrease of perpendicular anisotropy can be attributed to soft magnetic Fe being exchange coupled to FePt. We conclude that electrical charging of exchange coupled composite films allows tuning the magnetic properties reversibly over a broad range.