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MA: Magnetismus
MA 18: Magnetische Dünne Schichten II
MA 18.1: Vortrag
Donnerstag, 14. März 2002, 16:30–16:45, H22
Exchange splitting and charge carrier spin-polaization in EuO — •L. H. Tjeng1,2, P. G. Steeneken2, I. Elfimov2, G. A. Sawatzky2, G. Ghiringhelli3, N. B. Brookes3, and D.-J. Huang4 — 1II. Physikalisches Institut, Universität zu Köln — 2Solid State Physics Laboratory, University of Groningen, The Netherlands — 3ESRF, Grenoble, France — 4SRRC, Hsinchu, Taiwan
EuO is a semiconductor with a band gap of about 1.2 eV and is one of the very rare ferromagnetic oxides. Its Curie temperature is around 69 K. EuO becomes metallic below Tc and the metal-insulator transition (MIT) is very spectacular: the resistivity can drop by as much as 8 orders of magnitude. Moreover, an applied magnetic field causes a colossal magnetoresistance (CMR) with changes in resistivity of up to 6 orders of magnitude, i.e. much more extreme than in manganates.
We have succeeded in making high quality thin films of EuO, which allows us to carry out spin-resolved electron spectroscopic studies. Using a new type of spin-resolved X-ray absorption technique, we are able to measure the spin polarization of the conduction band. We observed large changes in the electronic structure upon crossing the Curie and MIT temperature. We found these to be caused by the exchange splitting of the conduction band in the ferromagnetic state, which is as large as 0.6 eV. We also found that the bottom of the conduction band consists of majority spins only. This implies that the (doped) charge carriers in EuO are practically fully spin-polarized, making the material very interesting for spintronic research.