Tailored Properties of Ferromagnetic Thin Films

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…


1 Introduction
2 Sample Fabrication
2.1 The Substrate
2.2 Thermal Evaporation
2.2.1 Resistive Evaporation
2.2.2 Electron Beam Evaporation
2.3 Molecular Beam Epitaxy
2.4 Magnetron Sputter Deposition
2.5 Nanostructure Patterning
3 Characterization Techniques
3.2 MFM
3.2.1 Principle of Operation
3.2.2 Tip-Sample Interaction
3.3 Electrical Measurements
3.3.1 Power Calibration
3.3.2 Sample Magnetoresistance
3.3.3 Homodyne Detection
4 Micromagnetism
4.1 Energetics
4.1.1 Zeeman Energy
4.1.2 Exchange Energy
4.1.3 Demagnetization Energy
4.2 Magnetic Anisotropy
4.2.1 Magnetocrystalline Anisotropy
4.2.2 Surface Anisotropy
4.2.3 Interface Anisotropy
4.2.4 Magnetoelastic Anisotropy
4.2.5 Induced Anisotropy
4.3 The Effective Field
4.4 The Exchange Length
4.5 Landau-Lifshitz Equation
4.6 Landau-Lifshitz-Gilbert Equation
4.7 The Damping Parameter
4.8 Gilbert Damping versus Landau-Lifshitz Damping
4.9 Spin-Transfer Effects
4.9.1 Adiabatic Spin-Transfer
4.9.2 Non-Adiabatic Spin-Transfer
4.9.3 The Spin Polarization
5 Properties of Magnetic Domain Walls
5.1 The Origin of Domains
5.2 Different Types of Domain Walls
5.2.1 Domain Wall Type Phase Diagram
5.3 Nucleation of Domain Walls
5.3.1 Field Sequence Dependent Nucleation
5.4 Pinning of Domain Walls
5.5 Materials with Uniaxial Anisotropy
5.6 Manipulation of Domains and Domain Walls
5.7 Characterizing Domain Walls with MFM
5.8 Vortex Resonance
6 Diluted Magnetic Semiconductors
6.1 The Ferromagnetic Transition Temperature
6.2 Defects in Ga1-xMnxAs
6.3 Enhancement of Tc by Post Growth Annealing
6.4 Origin of Ferromagnetism in Ga1-xMnxAs
7 Controlled Motion of Magnetic Particles
7.1 The Magnetic Particles
7.2 The Elliptical Elements
7.3 Transport and Separation Principles
8 Summary in Swedish
9 Acknowledgements

Author: Warnicke, Peter

Source: Uppsala University Library

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