This title appears in the Scientific Report :
2003
Please use the identifier:
http://hdl.handle.net/2128/193 in citations.
Magnetische Strukturen in [Er\Tb]-Schichtsystemen: Einfluß der magnetischen Nachbarschaft und konkurrierender Anisotropien
Magnetische Strukturen in [Er\Tb]-Schichtsystemen: Einfluß der magnetischen Nachbarschaft und konkurrierender Anisotropien
The present work concerns the influence of the artificial superstructure and competing anisotropies on the magnetic structure in [Er$\vert$Tb] superlattices. Combining neutron diffraction and resonance x-ray magnetic scattering (RXMS) the long range magnetic ordering of localized 4f states can be re...
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Personal Name(s): | Voigt, Jörg (Corresponding author) |
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Contributing Institute: |
Streumethoden; IFF-STM |
Imprint: |
Jülich
Forschungszentrum Jülich GmbH Zentralbibliothek, Verlag
2003
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Physical Description: |
II, 144 p |
Dissertation Note: |
Aachen, Techn. Hochsch., Diss., 2003 |
Document Type: |
Book Dissertation / PhD Thesis |
Research Program: |
Kondensierte Materie |
Series Title: |
Berichte des Forschungszentrums Jülich
4087 |
Subject (ZB): | |
Link: |
OpenAccess |
Publikationsportal JuSER |
The present work concerns the influence of the artificial superstructure and competing anisotropies on the magnetic structure in [Er$\vert$Tb] superlattices. Combining neutron diffraction and resonance x-ray magnetic scattering (RXMS) the long range magnetic ordering of localized 4f states can be related to a coherent spin density wave in the conduction bands of both Er and Tb. The direct observation of spin density wave was made possible only by the improvements of the RXMS technique, i.e., an excellent source at the beamline 6id-b of the APS at the Argonne National Lab and a very efficient polarization analysis to distinguish the magnetic signal from the much stronger charge scattering. To understand the magnetic behavior of a superlattice an precise knowledge of the structural properties is needed. Therefore the growth process for epitaxial multilayers was optimized by in situ low energy electron diffraction and Auger electron spectroscopy. Following recipes given in literature for other rare earth systems, the growth parameters have been adjusted for Er and Tb. In a superlattice the quality of the interfaces is particularly important. Their properties in complete multilayers have been analysed ex situ by grazing incidence x-ray diffraction. The interfaces extend over 3-4 atomic layers, but the roughness is vertically correlated, as seen by the diffuse scattering. Therefore a squared interface profile is obtained locally even for small layer thicknesses. Wide angle diffraction of neutrons and x-ray confirms the squared structure of [Er$_{n_{Er}} \vert Tb_{n_{Tb}}$] superlattices, the indices denoting the layer thickness in atomic layers, with up to 150 repetitions of one bilayer unit. Ferromagnetic order sets in at a temperature of 230 K, if the Tb layer thickness is more then 20 atomic layers. The ferromagnetic blocks are coupled, depending on temperature and interlayer thickness. Bulk Tb undergoes a phase transition to a helical magnetic structure at this temperature. The suppression of the bulk helical structure in Tb is due to epitaxial strains within the superlattice. In contrast the [Er$_{20} \vert Tb_{5}$] sample forms a modulated magnetic structure below 150 K. Additionally basal plane ferromagnetic order appears below 40 K, with an antiferromagnetic coupling of ordered layers. The RXMS results confirm the existence of a common superlattice band structure which is responsible for the magnetic proximity effects. A common electronic band structure is found in an Er$_{0,8}$Tb$_{0,2}$ film, too. The comparison with the superlattice clarifies the difference between statistical lattice site occupation and an artificial superstructure. This opens the opportunity of tailored magnetic properties by a man made structure. |