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Department of Physics

Multilayer Systems

Multilayer systems with combinations of insulators, semiconductors and ferromagnets are of great importance for various electrical devices such as spintronic devices. In particular, the properties of the surfaces and interfaces between the insulating layers have a great influence on physical effects, such as tunnel magnetoresistance (TMR) or giant magnetoresistance (GMR).

The so-called magnetic tunnel junctions (MTJ) are devices that utilize TMR. In them, electrons pass between two ferromagnetic electrodes through a thin insulating layer depending on their magnetization. The thickness of the insulating barrier as well as the structure of the layers and interfaces have a great influence on the TMR effect. Not only the structural but also the chemical and magnetic properties are of current interest in the diverse research.

Favorable materials for MTJ devices are magnesium oxide (MgO) as an insulator with a large band gap, iron (Fe) or cobalt (Co) as a ferromagnetic component, and gallium arsenide (GaAs) as a semiconductor due to the possibility of band gap variation and its high electron transmission frequency.

Grafik eines Mehrschichtsystems bestehend aus einem Silber-Substrat, Graphen und einem Capping Layer © Lukas Kesper​/​TU Dortmund
For example, a material consisting of several layers changes its electronic properties.

Both systems have been studied in detail in terms of structure determination and investigation of electronic, chemical and magnetic properties.