Doped BiFeO3 Nanoparticles

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Magnetoelectric materials have been intriguing researchers for several decades. Intrinsic multiferroics exhibit such coupling usually at temperatures well below room temperature. So far, only a few room temperature multiferroics are known, all exhibiting an antiferromagnetic order at room temperature which yields practically vanishing effective magnetoelectric coupling. The most interesting candidate is bismuth ferrite, BiFeO3, because the magnetic moments are not antiparallel per se, but generate cycloidal order across many unit cells. Overall these moments cancel, but hope is to break up or modify this order and establish a finite magnetic moment of reasonable magnitude for applications. So far, bulk doping and thin film formation have been the major routes trying to tailor these properties. In doped nanoparticles the additional influence of the huge surface area is anticipated to modify the cycloidal order as well as to enhance magnetoelectric coupling. Not much is known on the effect of co-doping and nanoparticle surface decoration with secondary magnetic particles. This proposal deals with making and investigating these particles. In this initial proposal mostly doped and co-doped variants will be addressed. The major part of the project is focused on chemical synthesis based on an in house developed route similar to the sol-gel or organosol methods. We have been producing a multitude of different ceramic nanoparticles including core shell and raspberry structures at the nanoscale. Making of nominally pure BiFeO3 has been very successful. These techniques are now intended to be applied to co-doped BiFeO3. Characterization comprises classical techniques, SQUID magnetometry, impedance analysis (also locally), and scanning probe microscopy techniques. In order to vary particle size, not only the chemical route is intended for use, but also laser synthesis and processing routes yielding mostly smaller particle sizes than the chemical techniques. Thus the whole range from 20 to 1000 nanometers can be covered. Like everyone else, we hope to enhance the effective magnetic moment of the particles and magnetoelectric coupling. We offer a promising new approach.