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11	Electronic structure and magnetism of selected materials Chiuzbaian, Gheorghe Sorin 30 July 2003 (has links) The details of the interplay between the electronic structure and the magnetic properties of matter represent a state of the art challenge. In the present work spectroscopic investigations on the electronic structure of some interesting materials are presented. The achieved information has been used in order to answer specific questions related to the magnetic behavior of the investigated materials. For the transition metal dicyanamide compounds it is shown that the electronic states arising from carbon and nitrogen remain roughly unchanged for all compositions. A model for the magnetic superexchange interaction was proposed. In this model the geometry of the crystallographic structure accounts for a particular interaction pattern while the occupancy of the 3d transition metal band is the factor which triggers the changeover from antiferromagnetic to ferromagnetic interaction. In the case of six-membered ferric-wheel molecules the comparison between experimental and theoretical data issued estimations for the magnitude of magnetic exchange interactions. The information on the electronic structure of the LaNi5-xMex (Me=Cu, Al) allowed a better understanding of their magnetic behavior. The changes induced in the electronic structure of the parent compound by partial substitutions of nickel by copper or aluminum are discussed. electronic structure XPS XES metal-organic compounds intermetallic compounds 29 - Physik, Astronomie 75.50.Xx - Molecular magnets ddc:540
12	Theoretical investigation of size effects in multiferroic nanoparticles Allen, Marc Alexander 05 August 2020 (has links) 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. / Graduate 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

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Electronic structure and magnetism of selected materials

Theoretical investigation of size effects in multiferroic nanoparticles