| 1. |
- Warnicke, Peter, 1978-
(författare)
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Tailored Properties of Ferromagnetic Thin Films
- 2008
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Magnetic thin films and patterned nanostructures have been studied with respect to their magnetic properties using SQUID-magnetometry, magnetic force microscopy, electrical measurements, and micromagnetic calculations. Properties of vortex domain walls, trapped in Permalloy nanowires with artificial constrictions, were investigated experimentally and by numerical calculations. In particular, the geometrical extent and strength of the pinning potential were evaluated. In these wires, long-range vortex domain wall displacement induced by spin polarized alternating currents was obtained numerically at reduced threshold current densities as compared with the direct current case. Due to the asymmetry of the energy potential, the long-range displacement direction is determined by the vortex chirality. Strained FeCo/Pt superlattices with strong perpendicular anisotropy were investigated experimentally. The strain was controlled by varying the thickness of each alternating layer with monolayer precision and was found to have a dominating effect on the total anisotropy. Epitaxial films of the diluted magnetic semiconductor (Ga,Mn)As were studied with focus on how the ferromagnetic transition temperature could be controlled by post-growth annealing. The ferromagnetic transition temperature was enhanced by approximately 85% for a Mn-doping concentration of 6% under certain conditions. A method to manipulate micrometer sized magnetic particles on patterned arrays of elliptical Permalloy microstructures was studied. Controlled motion and separation of the magnetic particles were obtained using applied rotating magnetic fields. The domain structure of the elliptical elements was studied numerically.
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| 2. |
- Boulle, Olivier, et al.
(författare)
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Non-adiabatic spin transfer torque in high anisotropic magnetic nanowires with narrow domain walls
- 2008
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Ingår i: Physical Review Letters. - 0031-9007 .- 1079-7114. ; 101:21, s. 1-4
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Tidskriftsartikel (refereegranskat)abstract
- Current induced domain wall (DW) depinning of a narrow DW in out-of-plane magnetized (Pt/Co)3/Pt multilayer elements is studied by magnetotransport. We find that for conventional measurements Joule heating effects conceal the real spin torque efficiency and so we use a measurement scheme at a constant sample temperature to unambiguously extract the spin torque contribution. From the variation of the depinning magnetic field with the current pulse amplitude we directly deduce the large nonadiabaticity factor in this material and we find that its amplitude is consistent with a momentum transfer mechanism.
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| 3. |
- Warnicke, Peter
(författare)
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Asymmetric energy potential of pinned domain walls at constrictions
- 2008
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Ingår i: Applied Physics Letters. - : AIP Publishing. - 0003-6951 .- 1077-3118. ; 93:17, s. 172508-
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Tidskriftsartikel (refereegranskat)abstract
- The pinning properties of magnetic vortex domain walls were experimentally investigated in patterned nanowires with artificial constrictions. Domain walls were nucleated and depinned by applied magnetic fields and observed with magnetic force microscopy. It was found that the pinning strength is dependent on the chirality of the vortex wall. Micromagnetic simulations confirm these results and reveal the energy potential of the pinned domain wall, including the width of the pinning site.
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| 4. |
- Warnicke, Peter, et al.
(författare)
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Long-range vortex domain wall displacement induced by an alternating current : Micromagnetic simulations
- 2008
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Ingår i: Physical Review B. Condensed Matter and Materials Physics. - 1098-0121 .- 1550-235X. ; 78:1, s. 012413-
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Tidskriftsartikel (refereegranskat)abstract
- A magnetic vortex domain wall, confined in a Permalloy nanowire with periodically varying width, is brought to resonance and long-range motion by means of a spin-polarized alternating current in micromagnetical simulations. The long-range direction of motion is found to be dependent on the vortex chirality but independent of the vortex polarity. Compared to the case where a direct current is used to move the vortex domain wall, the threshold current density for long-range motion is significantly reduced.
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