Theoretical investigation of size effects in multiferroic nanoparticles




Allen, Marc Alexander

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Over the last two decades, great progress has been made in the understanding of multiferroic materials, ones where multiple long-range orders simultaneously exist. However, much of the research has focused on bulk systems. If these materials are to be incorporated into devices, they would not be in bulk form, but would be miniaturized, such as in nanoparticle form. Accordingly, a better understanding of multiferroic nanoparticles is necessary. This manuscript examines the multiferroic phase diagram of multiferroic nanoparticles related to system size and surface-induced magnetic anisotropy. There is a particular focus on bismuth ferrite, the room-temperature antiferromagnetic-ferroelectric multiferroic. Theoretical results will be presented which show that at certain sizes, a bistability develops in the cycloidal wavevector. This implies bistability in the ferroelectric and magnetic moments of the nanoparticles. This novel magnetoelectric bistability may be of use in the creation of an electrically-written, magnetically-read memory element.



bismuth ferrite, bfo, nanoparticle, nanomagnetism, multiferroics, optimization, magnetism, ferroelectric, bistability, anisotropy, surface anisotropy, weak ferromagnetism, antiferromagnetism, Dzyaloshinskii-Moriya interaction, cycloid, numerical methods, condensed matter, solid state physics, magnetoelectric effect, room-temperature multiferroic, superexchange, magnetic memory, spin canting, g-type antiferromagnetism, Heisenberg Hamiltonian, Nelder-Mead, L-BFGS-B, mathematica, python, ferroelectricity, perovskite, antiferromagnet, bifeo3, rhombohedral, pseudocubic, r3c, trigonal, physics, magnetic, memory, electrically-written memory, curie temperature, néel temperature, materials science