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作者 Sterbinsky, George Evan
書名 Structural and magnetic properties of magnetoelectric oxide heterostructures deposited by molecular beam epitaxy
國際標準書號 9781109742565
book jacket
說明 249 p
附註 Source: Dissertation Abstracts International, Volume: 71-05, Section: B, page:
Adviser: Bruce W. Wessels
Thesis (Ph.D.)--Northwestern University, 2010
There is considerable interest in incorporating magnetic materials into electronic devices to achieve new functions such as nonvolatile memories. Electric field control of magnetism is of much interest for new low power electronic devices because it eliminates the need to apply magnetic fields. One approach to achieving electrical control of magnetism is to exploit magnetoelastic effects in composites of ferromagnetic and ferroelectric materials. Application of an electric field to the composite will induce a strain through the piezo-electric effect, and the strain will alter the magnetization of the ferromagnetic constituent through the magnetoelastic effect. In this work, we examine the relationships between growth, strain, and magnetic properties of epitaxial ferrimagnetic Fe3O4 (magnetite) and ferroelectric BaTiO3 thin film heterostructures. We find that altering the strain state of a magnetite layer deposited on a BaTiO3 substrate has a profound effect on its magnetization. Here, we demonstrate the interaction between strain and magnetization is mediated by magnetic anisotropy and the magnetic domains structure of the films
Epitaxial magnetite films were deposited on MgO, BaTiO3, and SrTiO3 substrates by molecular beam epitaxy between temperatures of 573 and 723 K. Examination of the morphologies of Fe3O 4 films indicates that island growth is favored. Films exhibit in-plane magnetic isotropy and reduced saturation magnetizations with respect to the bulk material, as demonstrated by superconducting quantum interference device magnetometry. Magnetic hysteresis measurements suggest that these differences originate from antiphase boundary defects within the films
The strain in magnetite films deposited on BaTiO3 single crystal substrates was measured by x-ray diffraction. Measurements reveal a dependence of magnetization (M) on strain (epsilon) with discontinuities in magnetization versus temperature curves resulting from changes in the domain structure of the BaTiO3 at its phase transitions. Changes in strain are also found to alter the magnetic domain structure of the Fe3O 4 films. Values of DeltaM=Deltaepsilon as large as -2.1x104 emu/cm3 have been observed at 280 K. The resultant strain in the magnetite film modifies the magnetocrystalline anisotropy and thereby changes its magnetization. The magnetoelastic contribution to the magnetic anisotropy was calculated from the measured strain and is consistent with observed changes in magnetization
School code: 0163
Host Item Dissertation Abstracts International 71-05B
主題 Engineering, Materials Science
0794
Alt Author Northwestern University. Materials Science and Engineering
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