A1: Nanoscale multiferroic heterostructures
We investigate the relations between preparation conditions, microstructure, and properties of nanoscale multiferroic heterostructures. In a first approach, superlattices consisting of a ferri- or ferromagnetic (FM) and a ferroelectric (FE) oxide will be prepared, whereby lattice mismatch, crystal orientation, and thickness of the individual layers will be varied. In a second approach, arrays consisting of epitaxial nanodots of one material (FM or FE) will be prepared in a matrix of the second material (correspondingly FE or FM). Here, lattice mismatch, crystal orienatation, as well as lateral size and pitch of the nanodots will be varied. In a third approach, nanowires and nanotubes consisting of combinations of FE and FM oxides will be studied.
The combination of ferroelectric and (ferro-, ferri- or antiferro-)magnetic properties, either within the same material (intrinsic ferroelectromagnets, intrinsic multiferroics) or by intimate contact between two dissimilar materials (extrinsic multiferroics) is considered to be promising for new types of memory elements or actuators and sensors with a wider spectrum of properties. On the other hand, such materials and structures are expected to permit deep insight into basic mechanisms of the interaction between different ferroic properties. Presently both these types of multiferroics are under intensive investigations worldwide. In case of an extrinsic ferroelectromagnet, the intimate intergrowth of the FE and the FM material on the nanometer scale is particularly promising in view of a strong interaction between the magnetic and ferroelectric properties. As a mechanism of this interaction, the elastic interaction via the piezoelectric and magnetostrictive properties of the components is usually considered; however, also other interaction mechanisms should be possible, e.g., via the mutual influence onto the electronic structure of the components at the common interfaces.
Exceeding presently known approaches, within 12 years a three-step program on preparation, microstructure characterization and property analysis of nanoscale ferroelectromagnetic heterostructures will be pursued. In a first step, FM/FE superlattices with lattice mismatch, crystal orientation, and thickness of the individual layers as variables will be investigated. In a second step, arrays of well-orderly arranged nanodots of one material within the matrix of the complementary second material will be prepared, varying lattice mismatch, crystal orientation, lateral size, and pitch of the nanodots. In a third step, arrays made of nanowires and nanotubes consisting of radially arranged layer combinations of FM and FE materials will be studied. The required preparation methods have been developed in the group in recent years. Pulsed laser deposition, in part using stencils (deposition masks) with well-orderly arranged nanosize holes, as well as chemical solution deposition into well-ordered macroporous silicon and anodic alumina substrates are available. As FE materials, BaTiO3 and Pb(Zr,Ti)O3 will be used, and as FM materials different ferrimagnetic spinels (spinel ferrites) of type CoFe2O4. The latter, being electrical insulators, allow to apply an electric field (in order to switch the ferroelectric component) even to those samples where the magnetic component extends in the direction of the electric field. Overall we hope to obtain insight into the nature and strength of the FM-FE interaction and into interactions between preparation conditions, microstructure, and properties of nanoscale multiferroic heterostructures.
Principal Investigators
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Prof. Dr. Dietrich Hesse ⇒
phone: +49 (0) 345/55 82741 fax: +49 (0) 345/55 11223 |
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Dr. Marin
Alexe ⇒
phone: +49 (0) 345/55 82705 fax: +49 (0) 345/55 11223 |
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