Ferromagnetic Semiconductors

Dear Colleagues,

In the last few years diluted ferromagnetic semiconductors have experienced a dramatic upsurge of interest due to their very promising potential for technological applications, on the one hand, and being attractive from a fundamental physics point of view, on the other. These materials might be able to integrate data processing (semiconductor technique: electron charge) and storage (ferromagnetism technique: electron spin) on a single chip. The simultaneous exploitation of charge and spin is known as “spintronics”. Undoubtedly ferromagnetism in such semiconducting materials would open the door for exciting microelectronic device applications provided the following non-trivial boundary conditions were fulfilled: (1) The Curie temperature should clearly exceed room temperature, (2) the charge carriers should react sensitively on changes in the magnetic state, and (3) the material should retain its excellent semiconductor properties. The simultaneous achievement of these objectives has been in the last years and continues to be the main goal of intense experimental as well as theoretical research on (diluted) ferromagnetic semiconductors.
The classical ferromagnetic semiconductors EuO and EuS have been investigated for several decades and are considered as rather well understood. For application, however, they do not come into question because of too low transition temperatures and only poor semiconductor properties. On the other hand, however, they may help to work out the basic physics of ferromagnetic semiconductors. More promising for future applications are (III,V) semiconductors doped with magnetic ions such as the prototypical Mn-doped GaAs with Curie temperatures well above 100K. Both localized magnetic moments and itinerant charge carriers are provided by the magnetic ion. Since the quality of the samples and their magnetic properties seem to be closely connected material science of growth and defects plays an important role with respect to spintronics aspects of such materials.
From a basic theoretical point of view the interplay between electronic structure, exchange interaction and moment disorder with respect to electric, magnetic and transport properties must be understood. By proper modelling and reliable many-body evaluation of the decisive magnetic correlations as well as “ab initio” calculations of real materials one can hope to get a better understanding of the fundamental physics of the ferromagnetism that occurs in (diluted) ferromagnetic semiconductors and of the prerequisites necessary for getting sufficiently high Curie temperatures.

Prof. Dr. Wolfgang Nolting
Guest Editor