Ferromagnetic-Ferroelectric Domain Coupling in Multiferroic Heterostructures

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School of Science | Doctoral thesis (article-based) | Defence date: 2013-06-27
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79 + app. 40
Aalto University publication series DOCTORAL DISSERTATIONS, 106/2013
In this thesis, strain-mediated coupling between magnetic films and ferroelectric BaTiO3 substrates with regular ferroelastic domain structures is studied. Using optical polarization microscopy, it is shown that imprinting of ferroelectric domains into magnetic polycrystalline CoFe, amorphous CoFeB and crystalline Fe films can be achieved. The ferroelectric polarization and elongated c-axis of the BaTiO3 substrates rotate by 90o at ferroelectric domain boundaries. Transfer of this strain to the adjacent magnetic film induces local magnetoelastic anisotropy whose orientation and symmetry depends on the underlying ferroelectric domain. Furthermore, abrupt changes in the magnetoelastic anisotropy pin the magnetic domain walls onto the ferroelectric domain boundaries. As a result, the magnetic domain walls do not move in an applied magnetic field resulting in the formation of magnetically charged and uncharged domain walls at different field directions. The strong coupling between magnetic and ferroelectric domains is used to demonstrate local magnetic switching and magnetic domain wall motion by purely electrical means. It is shown that a regular magnetic stripe pattern can be reversibly written and erased by the application of an electric field across the BaTiO3 substrate. Moreover, the magnetic domain walls are dragged along by their ferroelectric counterpart in an external electric field. Both effects are explained by 90o rotations of the ferroelectric polarization and the resulting strain-induced modification of the local magnetoelastic anisotropy. Similar strain-mediated effects, including local in-plane magnetization rotation by 90o, are obtained when the multiferroic heterostructures are cooled or heated through the structural phase transitions of BaTiO3.
Supervising professor
van Dijken, Sebastiaan, Prof., Aalto University, Finland
Thesis advisor
van Dijken, Sebastiaan, Prof., Aalto University, Finland
ferromagnetic, ferroelectric, multiferroic, magnetism, magnetic domain, electric field control of magnetism, Barium Titanate
Other note
  • [Publication 1]: Tuomas H. E. Lahtinen, Jussi O. Tuomi, Sebastiaan van Dijken. PatternTransfer and Electric-Field Induced Magnetic Domain Formation in Multiferroic Heterostructures. Advanced Materials, 23, 3187-3191, September 2011.
  • [Publication 2]: Tuomas H. E. Lahtinen, Jussi O. Tuomi, Sebastiaan van Dijken. Electrical Writing of Magnetic Domain Patterns in Ferromagnetic/Ferroelectric Heterostructures. IEEE Transactions on Magnetics, 47, 3768-3771, October 2011.
  • [Publication 3]: Tuomas H. E. Lahtinen, Kévin J. A. Franke, Sebastiaan van Dijken. Electric-Field Control of Magnetic Domain Wall Motion and Local Magnetization Reversal. Scientific Reports, 2, 258, February 2012.
  • [Publication 4]: Kévin J. A. Franke, Tuomas H. E. Lahtinen, Sebastiaan van Dijken. Field Tuning of Ferromagnetic Domain Walls on Elastically Coupled Ferroelectric Domain Boundaries. Physical Review B, 85, 094423, March 2012.
  • [Publication 5]: Tuomas H. E. Lahtinen, Yasuhiro Shirahata, Lide Yao, Kévin J. A. Franke, Gorige Vemkataiah, Tomoyasu Taniyama, Sebastiaan van Dijken. Alternating Domains with Uniaxial and Biaxial Magnetic Anisotropy in Epitaxial Fe Films on BaTiO3. Applied Physics Letters, 101, 262405, December 2012.
  • [Publication 6]: Tuomas H. E. Lahtinen, Sebastiaan van Dijken. Temperature Control of Local Magnetic Anisotropy in Multiferroic CoFe/BaTiO3. Applied Physics Letters, 102, 112406, March 2013.