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| Home > Publications database > Exchange Interactions and Induced $Eu^{3+}$ Magnetic Order in $RMnO_{3}$ Investigated Using Resonant X-ray Diffraction |
| Home > Publications database > Exchange Interactions and Induced $Eu^{3+}$ Magnetic Order in $RMnO_{3}$ Investigated Using Resonant X-ray Diffraction |
| Book/Dissertation / PhD Thesis | PUBDB-2015-01676 |
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2015
Verlag Deutsches Elektronen-Synchrotron
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Please use a persistent id in citations: doi:10.3204/DESY-THESIS-2015-011
Report No.: DESY-THESIS-2015-011
Abstract: The so-called multiferroics, materials that concomitantly exhibit more than one ferroic order, have in recent years attracted much attention owing totheir possible applications in high density data storage, high sensitivity ac magnetic field sensors and novel spintronic devices. In particular, multifer-roics with strong magnetoelectric coupling are more attractive. Among such multiferroics, an interesting special class is the orthorhombic manganiteswith perovskite structure. In these compounds, frustration serves to destabilize ordinary ferromagnetic or antiferromagnetic ordering, giving rise to richphase diagrams due to several competing magnetic interactions. Interactions between strong rare earth magnetic moments and weaker transition metalmoments add another level of complexity, as well as interest. The current dissertation presents results obtained investigating the mag-netic structure responsible for ferroelectricity in a few selected multiferroic compounds, using x-ray resonant magnetic scattering (XRMS). In particular,single crystals of Eu1−xYxMnO3 have been studied at low temperatures and in high magnetic fields. This series of compounds is similar in structure tothe heavily studied RMnO3 (R=Tb,Gd,Dy), only without rare earth magnetism. The novel technique of full polarization analysis has been used todetermine the complicated cycloidal Mn magnetic ordering, and additional components due to the Dzyaloshinskii-Moriya interactions have been iden-tified. In the compound Eu0.8Y0.2MnO3, two coexisting multiferroic phases were observed, and a magnetoelectric coupling between the two was established. Moreover, magnetic order of the formally non-magnetic rare earth ion Eu3+ was observed in the same compound. It has been concluded toresult from a Van Vleck type excitation of the J = 0 ground state due to the symmetry-breaking internal exchange field from the Mn magnetic moments.In addition, this dissertation reports on high field investigations of the complex low-temperature phases of GdMnO3 as well as high energy non-resonant scattering studies of TbMnO3. In the case of TbMnO3, the simple high energy magnetic cross section allowed for direct determination of spincomponents in the ferroelectric phase. In the case of GdMnO3, the first high field XRMS investigation below the Gd ordering temperature was performed, revealing an important role of the symmetric exchange interaction between the Gd and Mn subsystems for stabilizing ferroelectricity in the compound.
Keyword(s): Dissertation
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