Sam Seddon , Department of Physics, University of Warwick Coventry, UK
Local investigations of coupled order parameters in multiferroics
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Multiferroic materials possess more than one ferroic order as exemplified by a material such as boracites which below their ordering temperature are simultaneously both ferromagnetic (spontaneous magnetization) and ferroelectric (spontaneous electrical polarization). The search for multiferroic functional materials continues apace but there are challenges in finding materials where these ferroic ordering parameters are not independent from each other, rather than coupling in complex ways. Beyond the coupling mechanism between the ferroic orders, the inherent symmetry breaking within them leads to the formation of new and unexplored topological spin and polarization textures. In this presentation three different material systems with varying degrees of order-parameter coupling are explored. The nature of the different couplings are studied by bulk magnetometry, electrical measurements and local Magnetic Force Microscopy (MFM) / Piezoresponse Force Microscopy (PFM) measurements. We use a low-temperature Attocube instrument to explore the effects of the ferroelastic pinning between the crystal structure and magnetic moments in Fe7S8 and show that one can extract magnetic hysteresis from MFM measurements. The same apparatus is used to show a topological-like Hall response in SrRuO3/PbTiO3 (ferromagnetic/ferroelectric) thin films through MFM which is explained through a chiral, non-topological spin texture. Finally novel PFM measurements made on a single crystal of Fe3O4, itself a ferroelectric, ferromagnet and ferroelastic multiferroic, will be shown.
Sam Seddon is currently in the final months of his PhD, funded on a ‘functional domain walls’ EPSRC (Engineering and Physical Sciences Research Council) grant. As the principle user of the Attocube low-temperature atomic force microscopy system, his research has focussed around the correlation of low temperature scanning probe microscopy measurements with complementary bulk measurements. He previously studied for his BSc (Hons) at Warwick and later a MSc (by Research) which focussed on X-Ray Photoelectron Spectroscopy before moving to AFM, multiferroics and beyond.