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R. Grössinger et al.:
"Multifunctional Materials";
Vortrag: Moscow International Symposium on Magnetism (MISM 2008), Moscow, Russia (eingeladen); 20.06.2008 - 25.06.2008; in: "Moscow International Symposium on Magnetism, Book of Abstracts", (2008), ISBN: 978-5-8279-0072-6; S. 48.

Multifunctional materials are sensitive to different environmental properties (such as temperature, magnetic field, electric field etc.) which can be used for technical applications. This sensitivity can be achieved in single phase but more often in multiphase materials. Modern material science tries to use new ways of sample production to optimize such materials. Here especially wet chemical methods are often favourable. Within the here presented work examples of multifunctional materials which can be used in industry are given. Especially in composites the microstructure (grain size, interfacing) plays a very important role. The properties of magnetic materials are very sensitive to the grain size. In the last years it was shown that the magnetic properties (such as magnetization, losses, stored energy etc.) of soft magnetic as well as hard magnetic nanocrystalline materials were improved remarkable (see e.g. 1,2,3). Two steps were important for the improvement: i) reduction of the grain size to nanometers and ii) addition of a second phase with favourable properties. This leads to a remanence enhancement for hard magnetic materials but also to a remarkable improvement of soft magnetic properties (such as permeability etc.).
Also in materials with high magnetostriction these steps can improve the behaviour.
Producing these materials in a multiphase nanocrystalline state causes a drastic reduction of the anisotropy, however a high magnetostriction still remains. Interesting candidates are here RFe2 compounds (R = Tb,Sm).
The combination of magnetic and piezo-electric properties in one material leads to socalled magnetoelectric systems. These materials exhibit an electric charge applying a magnetic field or a magnetic moment applying an electric field. There exist only few single phase materials, which are called multiferroic, which exhibit such a behaviour, however generally only at low temperatures. The conditions as well as the state of art of suitable multiferroic composites will be shown. Also here a nanocrystalline state is favourable for achieving a high magnetoelectric coefficient. The application of magneto-electric composites which exhibit such a behaviour at room temperature may be in new sensors.
Beside this exist also other families of multifunctional materials which should be mentioned. These are magnetocaloric materials which can be used in refrigerator systems. These are in competition with thermoelectric systems which may also be used to cool devices. Both material families were not used for large scale applications because of material problems - as will be discussed.