Magnetoelektrische Eigenschaften von Manganat-Titanat Übergittern

Abstract

Magnetoelectric multiferroics are materials in which the order phenomena ferromagnetism and ferroelectricity coexist. Due to pronounced magnetic as well as electric susceptibility, this class of material is especially suitable for the study of magnetoelectric coupling phenomena. However, the coexistence of the ferroic orders has rarely been observed in single phase materials. Composites give the possibility to further study magnetoelectric effects Within this work, the combination of ferromagnetic La2/3Ca1/3MnO3 (LCMO) and ferroelectricBaTiO3 (BTO) constitutes a multiferroic composite, in which a magnetoelectric coupling can occur via the interfaces. LCMO-BTO superlattices have been deposited on MgO substrates with the metallorganic aerosol deposition technique. Using coplanar electrodes on the top of the films, dielectric properties have been measured by a capacitance bridge. The electric capacitance and the dielectric loss as a function of sample temperature and external magnetic field shall give information about potential magnetoelectric couplings. Comparison of the experimental results with model calculations of the dielectric characteristics of a Maxwell-Wagner-circuit shall clarify, to what extent the observed magnetocapacitance can be attributed to the colossal magnetoresistance (CMR), a well-known property of LCMO. To further study the influence of the superlattice interfaces on the magnetoelectric properties, an interface-modified superlattice has been fabricated, in which thin layers of LaMnO3 have been deposited at every LCMO-BTO interface. The modified sample, in comparison to a conventional one, exhibiting the same thicknesses of LCMO- and BTO-layers, first of all shows enhanced magnetic and transport properties. The effect of the modification and thus the influence of the interfaces is discussed within LCMO as a material possessing strong electronic as well as polaronic correlations.