| 1. |
- Magnus, Fridrik, et al.
(författare)
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Sequential magnetic switching in Fe/MgO(001) superlattices
- 2018
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Ingår i: Physical Review B. Condensed Matter and Materials Physics. - : American Physical Society. - 1098-0121 .- 1550-235X. ; 97:17
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Tidskriftsartikel (refereegranskat)abstract
- Polarized neutron reflectometry is used to determine the sequence of magnetic switching in interlayer exchangecoupled Fe/MgO(001) superlattices in an applied magnetic field. For 19.6 Å thick MgO layers we obtain a 90◦periodic magnetic alignment between adjacent Fe layers at remanence. In an increasing applied field the toplayer switches first followed by its second-nearest neighbor. For 16.4 Å MgO layers, a 180◦periodic alignment isobtained at remanence and with increasing applied field the layer switching starts from the two outermost layersand proceeds inwards. This sequential tuneable switching opens up the possibility of designing three-dimensionalmagnetic structures with a predefined discrete switching sequence
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| 2. |
- Moubah, Reda, et al.
(författare)
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Discrete Layer-by-Layer Magnetic Switching in Fe/MgO(001) Superlattices
- 2016
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Ingår i: Physical Review Applied. - : American physical society. - 2331-7019. ; 5:4
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Tidskriftsartikel (refereegranskat)abstract
- We report on a discrete layer-by-layer magnetic switching in Fe/MgO superlattices driven by an antiferromagnetic interlayer exchange coupling. The strong interlayer coupling is mediated by tunneling through MgO layers with thicknesses up to at least 1.8 nm, and the coupling strength varies with MgO thickness. Furthermore, the competition between the interlayer coupling and magnetocrystalline anisotropy stabilizes both 90 degrees and 180 degrees periodic alignment of adjacent layers throughout the entire superlattice. The tunable layer-by-layer switching, coupled with the giant tunneling magnetoresistance of Fe/MgO/Fe junctions, is an appealing combination for three-dimensional spintronic memories and logic devices.
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| 3. |
- Warnatz, Tobias
(författare)
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Magnetic Properties of Epitaxial Metal/Oxide Heterostructures
- 2021
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- The work in this dissertation is devoted to tailoring and studying magnetic properties of epitaxial metal/oxide heterostructures. The aim is to understand the fundamental principles governing these properties and how they affect each other. The acquired knowledge can prove useful for the development of future spintronic devices. A variety of experimental techniques is used to fabricate and characterize the epitaxial structures. For fabrication, a combination of direct-current and radio-frequency sputtering is used, whereas x-ray reflectivity and diffraction measurements are the main tools for the structural characterization of the heterostructures. The magnetic characterization of these structures is done by a combination of longitudinal magneto-optical Kerr-effect measurements, Kerr-microscopy and polarized neutron reflectometry. First, it is shown how strain affects the magnetic properties of metal/oxide heterostructures by comparing Fe/MgO and Fe/MgAl2O4 superlattices. Subsequently, an antiferromagnetic interlayer exchange coupling in Fe/MgO superlattices is revealed and attributed to a spin-polarized-tunneling mechanism. The coupling strength can be tuned by changing the MgO thickness leading to the stabilization of different remanent states as well as to different reversal mechanisms. It is shown that the interlayer exchange coupling in Fe/MgO superlattices is a consequence of two distinct components. These components can be interpreted as beyond-nearest-neighbor interactions and a contribution arising from the total thickness of the heterostructures.The interlayer exchange coupling is further investigated via temperature dependent magnetization measurements. It is shown that different remanent states and reversal mechanisms occur at different temperatures. Furthermore, a large increase in interlayer exchange coupling strength with reduced temperature is revealed. Finally, it is shown that Fe84Cu16/MgO superlattices exhibit a reduced magnetocrystalline anisotropy and interlayer exchange coupling strength, as compared to pure Fe/MgO superlattices. Patterning such Fe84Cu16/MgO superlattices in circular islands leads to an increased saturation field with decreasing island diameter.
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| 4. |
- Warnatz, Tobias, et al.
(författare)
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The impact of number of repeats N on the interlayer exchange in [Fe/MgO]N(001) superlattices
- 2021
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Ingår i: Scientific Reports. - : Springer Nature. - 2045-2322. ; 11
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Tidskriftsartikel (refereegranskat)abstract
- The strength of the interlayer exchange coupling in [Fe/MgO]N(001) superlattices with 2 <= N <= 10 depends on the number of bilayer repeats (N). The exchange coupling is antiferromagnetic for all the investigated thicknesses while being nine times larger in a sample with N = 4 as compared to N = 2. The sequence of the magnetic switching in two of the samples (N = 4, N = 8) is determined using polarized neutron reflectometry. The outermost layers are shown to respond at the lowest fields, consistent with having the weakest interlayer exchange coupling. The results are consistent with the existence of quantum well states defined by the thickness of the Fe and the MgO layers as well as the number of repeats (N) in [Fe/MgO]N(001)superlattices.
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| 5. |
- Warnatz, Tobias, et al.
(författare)
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The influence of diameter on the magnetic saturation in Fe 84 Cu 16 /MgO [001] multilayered islands
- 2020
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Ingår i: Journal of Magnetism and Magnetic Materials. - : Elsevier BV. - 0304-8853 .- 1873-4766. ; 496
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Tidskriftsartikel (refereegranskat)abstract
- The saturation field of circular islands, consisting of [Fe84Cu16/MgO]9Fe84Cu16 multilayers, increases with decreasing diameter of the islands. When the diameter of the islands is below 450 nm the field induced changes are dominated by a coherent rotation of the moment of the Fe84Cu16 layers. For diameters of 2 μm and larger, a signature of domain nucleation and evolution is observed. The changes in the saturation field with diameter of the islands are ascribed to the interplay between interlayer exchange coupling, stray field coupling at the edges and the crystalline anisotropy of the Fe84Cu16 layers.
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