| 1. |
- Magnus, Fridrik, et al.
(författare)
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Giant magnetic domains in amorphous SmCo thin films
- 2014
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Ingår i: Physical Review B. Condensed Matter and Materials Physics. - 1098-0121 .- 1550-235X. ; 89:22, s. 224420-1-224420-5
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Tidskriftsartikel (refereegranskat)abstract
- The potential for tuning of magnetic properties and the exceptional uniformity are among the features that make amorphous magnetic materials attractive for technology. Here it is shown that the magnetization reversal in amorphous SmCo thin films takes place through the formation of giant magnetic domains, over a centimeter across. The domain structure is found to be dictated by the direction of the imprinted in-plane easy axis and the film boundaries. This is a consequence of the size of the anisotropy and the structural uniformity of the films, which also allows the movement of millimeter-long domain walls over distances of several millimeters. The results demonstrate the possibility of tailoring the magnetic domain structure in amorphous magnets over a wide range of length scales, up to centimeters. Moreover, they highlight an important consequence of the structural perfection of amorphous films.
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| 2. |
- Magnus, Fridrik, et al.
(författare)
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Magnetostrictive properties of amorphous SmCo thin films with imprinted anisotropy
- 2014
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Ingår i: Physical Review B. Condensed Matter and Materials Physics. - 1098-0121 .- 1550-235X. ; 89:13, s. 134414-1-134414-6
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Tidskriftsartikel (refereegranskat)abstract
- We examine the magnetostriction in amorphous SmCo thin films with a composition in the range 4-27 at.% Sm. The magnetostriction increases significantly with increasing Sm content but is small compared to terbium-based ferromagnetic compounds, despite the large imprinted anisotropy. The magnetostriction and anisotropy both increase approximately linearly as the temperature is reduced. The magnetoelastic energy is found to be far smaller than the anisotropy energy so the magnetoelastic atomic displacements during growth cannot be the origin of the imprinted anisotropy. The anisotropy is only slightly altered by the application of large tensile stresses, indicating that the local strain fields involved in magnetostriction are not equivalent to the global strain produced by mechanical bending.
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| 3. |
- Magnus, Fridrik, et al.
(författare)
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Tunable giant magnetic anisotropy in amorphous SmCo thin films
- 2013
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Ingår i: Applied Physics Letters. - : AIP Publishing. - 0003-6951 .- 1077-3118. ; 102:16, s. 162402-
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Tidskriftsartikel (refereegranskat)abstract
- SmCo thin films have been grown by magnetron sputtering at room temperature with a composition of 2-35 at.% Sm. Films with 5 at.% or higher Sm are amorphous and smooth. A giant tunable uniaxial in-plane magnetic anisotropy is induced in the films which peaks in the composition range 11-22 at.% Sm. This cross-over behavior is not due to changes in the atomic moments but rather the local configuration changes. The excellent layer perfection combined with highly tunable magnetic properties make these films important for spintronics applications.
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| 4. |
- Moubah, Reda, et al.
(författare)
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Anisotropic Magnetostriction and Domain Wall Motion in Sm10Co90 Amorphous Films
- 2013
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Ingår i: APPL PHYS EXPRESS. - 1882-0778. ; 6:5, s. 053004-
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Tidskriftsartikel (refereegranskat)abstract
- We show that Sm10Co90 amorphous films exhibit anisotropic magnetostriction effects when a magnetic field is applied perpendicular to the imprinted easy axis of magnetization. At low applied fields (0-100 mT), we observe strong anisotropy in the field response. Parallel to the applied field, the strain scales linearly with the applied field while the strain perpendicular to the field direction ( easy axis) is close to the detection limit. This behavior is accompanied by zigzag domain wall motion with the corners pointing along the easy axis. The origin of the anisotropic magnetostriction is discussed.
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| 5. |
- 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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| 6. |
- Moubah, Reda, et al.
(författare)
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Strain induced changes in magnetization of amorphous Co95Zr5 based multiferroic heterostructures
- 2013
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Ingår i: AIP Advances. - : AIP Publishing. - 2158-3226. ; 3:2, s. 022113-
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Tidskriftsartikel (refereegranskat)abstract
- A clear change in the magnetic anisotropy in a layer of amorphous Co95Zr5 is obtained at the orthorhombic phase transition of the BaTiO3 substrate. The use of an amorphous buffer layer between the ferroelectric substrate and amorphous magnetic film shows that bulk strain governs the change in themagnetic anisotropy of our ferromagnetic-ferroelectric heterostructure. Moreover, we show that the thermal magnetization curves exhibit anisotropic behavior.
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| 7. |
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| 8. |
- Novoselova, Iuliia P., et al.
(författare)
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Large uniaxial magnetostriction with sign inversion at the first order phase transition in the nanolaminated Mn2GaC MAX phase
- 2018
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Ingår i: Scientific Reports. - London : NATURE PUBLISHING GROUP. - 2045-2322. ; 8
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Tidskriftsartikel (refereegranskat)abstract
- In 2013, a new class of inherently nanolaminated magnetic materials, the so called magnetic MAX phases, was discovered. Following predictive material stability calculations, the hexagonal Mn2GaC compound was synthesized as hetero-epitaxial films containing Mn as the exclusive M-element. Recent theoretical and experimental studies suggested a high magnetic ordering temperature and non-collinear antiferromagnetic (AFM) spin states as a result of competitive ferromagnetic and antiferromagnetic exchange interactions. In order to assess the potential for practical applications of Mn2GaC, we have studied the temperature-dependent magnetization, and the magnetoresistive, magnetostrictive as well as magnetocaloric properties of the compound. The material exhibits two magnetic phase transitions. The Neel temperature is T-N similar to 507 K, at which the system changes from a collinear AFM state to the paramagnetic state. At T-t = 214 K the material undergoes a first order magnetic phase transition from AFM at higher temperature to a non-collinear AFM spin structure. Both states show large uniaxial c-axis magnetostriction of 450 ppm. Remarkably, the magnetostriction changes sign, being compressive (negative) above T-t and tensile (positive) below the T-t. The sign change of the magnetostriction is accompanied by a sign change in the magnetoresistance indicating a coupling among the spin, lattice and electrical transport properties.
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| 9. |
- 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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