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9 results on '"Audehm, Patrick"'

1. Local breaking of the spin-orbit interaction: the microscopic origin of exchange bias in Co/FeMn

Author

Brück, Sebastian, Audehm, Patrick, Schütz, Gisela, and Goering, Eberhard

Subjects
Condensed Matter - Materials Science
Abstract

Modern magnetic thin film devices owe their success in large part to effects emerging from interlayer coupling and exchange interaction at interfaces. A prominent example is exchange bias (EB), a magnetic coupling phenomenon found in ferromagnet (F)/antiferromagnet (AF) systems. Uncompensated pinned moments in the AF couple to the F via the interface causing an additional unidirectional anisotropy. As a result, the hysteresis of the F is shifted. The existence of such pinned moments is nowadays accepted although their physical nature and origin is still unknown. Here we present a thorough spectroscopic investigation based on X-ray magnetic circular dichroism which does for the first time provide direct information about the physics of pinned magnetic moments. Our data clearly shows that the orbital magnetic moment, which is usually widely quenched in transition metal systems, is the driving force behind exchange bias in Co/FeMn.

Published
2009

2. Gepinnte Bahnmomente in magnetischen Heterostrukturen

Author

Audehm, Patrick and Audehm, Patrick

Abstract

In der vorliegenden Arbeit werden erstmals gepinnte Bahnmomente an einer Grenzschicht spektroskopisch nachgewiesen. Es wurde eine Co/FeMn Probe mit „Exchange Bias“ als Modellsystem mit hoher Symmetriebrechung verwendet. Um die vergrabene Grenzschicht artefaktfrei spektroskopisch zu untersuchen, wurde die Methode des XMCD (engl.: „X-Ray Magnetic Circular Dichroism“) weiterentwickelt. Die gepinnten Momente im Antiferromagneten besitzen nahezu ausschließlich Bahnmoment-Charakter. Dies wird durch ein atomar lokales „aufziehen“ einer „Spin-Bahn-Kopplungs-Feder“ erklärt. Über ein derartiges Verhalten wurde bisher nicht berichtet und es wurde somit auch in keinem theoretischen Modell vorausgesagt. Dieser Effekt sollte nicht nur bei Exchange-Bias Systemen, wie hier gezeigt, sondern auch in anderen, z.B. hartmagnetischen Systemen eine wichtige Rolle bzgl. der magnetokristallinen Anisotropieenergie spielen. Mit dem so verstandenen Probensystem trägt das daraus resultierende neue Modell zum besseren Verständnis der Verteilung der magnetischen Momente, und speziell der Bahnmomente, im Exchange Bias System bei.

Published
2016

3. Corrigendum: Interfacial dominated ferromagnetism in nanograined ZnO: a μSR and DFT study

Author

Tietze, Thomas, Audehm, Patrick, Chen, Yu–Chun, Schütz, Gisela, Straumal, Boris B., Protasova, Svetlana G., Mazilkin, Andrey A., Straumal, Petr B., Prokscha, Thomas, Luetkens, Hubertus, Salman, Zaher, Suter, Andreas, Baretzky, Brigitte, Fink, Karin, Wenzel, Wolfgang, Danilov, Denis, and Goering, Eberhard

Subjects
Corrigenda
Abstract

Diamagnetic oxides can, under certain conditions, become ferromagnetic at room temperature and therefore are promising candidates for future material in spintronic devices. Contrary to early predictions, doping ZnO with uniformly distributed magnetic ions is not essential to obtain ferromagnetic samples. Instead, the nanostructure seems to play the key role, as room temperature ferromagnetism was also found in nanograined, undoped ZnO. However, the origin of room temperature ferromagnetism in primarily non-magnetic oxides like ZnO is still unexplained and a controversial subject within the scientific community. Using low energy muon spin relaxation in combination with SQUID and TEM techniques, we demonstrate that the magnetic volume fraction is strongly related to the sample volume fraction occupied by grain boundaries. With molecular dynamics and density functional theory we find ferromagnetic coupled electron states in ZnO grain boundaries. Our results provide evidence and a microscopic model for room temperature ferromagnetism in oxides.

Published
2015

4. Correction: Corrigendum: Interfacial dominated ferromagnetism in nanograined ZnO: a μSR and DFT study

Author

Tietze, Thomas, primary, Audehm, Patrick, additional, Chen, Yu–Chun, additional, Schütz, Gisela, additional, Straumal, Boris B., additional, Protasova, Svetlana G., additional, Mazilkin, Andrey A., additional, Straumal, Petr B., additional, Prokscha, Thomas, additional, Luetkens, Hubertus, additional, Salman, Zaher, additional, Suter, Andreas, additional, Baretzky, Brigitte, additional, Fink, Karin, additional, Wenzel, Wolfgang, additional, Danilov, Denis, additional, and Goering, Eberhard, additional

Published
2015
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7. Interfacial dominated ferromagnetism in nanograined ZnO: a μSR and DFT study

Author

Tietze, Thomas, primary, Audehm, Patrick, additional, Chen, Yu–Chun, additional, Schütz, Gisela, additional, Straumal, Boris B., additional, Protasova, Svetlana G., additional, Mazilkin, Andrey A., additional, Straumal, Petr B., additional, Prokscha, Thomas, additional, Luetkens, Hubertus, additional, Salman, Zaher, additional, Suter, Andreas, additional, Baretzky, Brigitte, additional, Fink, Karin, additional, Wenzel, Wolfgang, additional, Danilov, Denis, additional, and Goering, Eberhard, additional

Published
2015
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