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MA: Fachverband Magnetismus

MA 4: Magnetic Coupling Phenomena/ Exchange Bias

MA 4.1: Vortrag

Montag, 22. März 2010, 11:00–11:15, H22

The origin of exchange bias, Observation of pinned orbital moments at iron L2,3 in FeMn/Co — •Patrick Audehm¹, Sebastian Brück², Gisela Schütz¹, and Eberhard Goering¹ — ¹Max Planck Institute for Metals Research, Heisenbergstrasse 3, 70569 Stuttgart, Germany — ²University of Würzburg, Physikalisches Institut. IV Am Hubland, D-97074 Würzburg, Germany

The exchange anisotropy was discovered by Meiklejohn and Bean in 1956. Since then there have been many attempts to model the behavior of a system with exchange bias effect. Exchange bias (EB) results in a shift of the hysteresis loop and secondly in an increase of the coercive field. We investigated a widely studied EB-system, consisting of polycrystalline iron (Fe)-manganese (Mn) as an antiferromagnet and cobalt as a ferromagnet. We used X-ray magnetic circular dichroism (XMCD) and x-ray resonant magnetic reflectivity (XRMR) at the Fe L2,3 and Mn L2,3 edges, simultaneously performed in surface sensitive total electron yield (TEY) and bulk sensitive total fluoresence yield (TFY) at room and low temperatures. For the first time, we measured pinned magnetic Fe moments in iron-manganese. Mn shows nearly no XMCD effect, while the Fe provides a sizeable signal from the rotatable moments and a very small (about 0.7 per mill of the total signal) signal from the pinned uncompensated moments. According to the well established sum rules of XMCD the non-rotatable Fe L2,3 edge spectra reveal nearly pure orbital character. These results suggest a different view on the origin of exchange bias, based on locally loaded spin-orbit-coupling, and new possibilities understanding the origin of EB.