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This dissertation presents a substantial contribution to a new field of material science, the investigation of the magnetic properties of 3D curved surfaces, achieved by using a self-assembled geometrical transformation of an initially planar membrane. Essential magnetic properties of thin films can be modified by the process of transforming them from a 2D planar film to a 3D curved surface. By investigating and controlling the reasons that influence the properties, it is possible to improve the functionality of existing devices in addition to laying the foundation for the future development of microelectronic devices based on curved magnetic structures. To accomplish this, it is necessary both to fabricate high-quality 3D curved objects and to establish reliable characterization methods based on commonly available technology. The primary objective of this dissertation is to develop techniques for characterizing the static and dynamic magnetic properties of self-assembled rolled 3D geometries. The second objective is to examine the origin of shape-, size- and strain/curvature-induced effects. The developed approach based on anisotropic magnetoresistance (AMR) measurement can quantitatively define the rolling-induced static magnetic changes, namely the induced magnetoelastic anisotropy, thus eliminating the need for microscopic imaging to characterize the structures. The interpretation of the AMR signal obtained on curved stripes is enabled by simultaneous visualization of the domain patterns and micromagnetic simulations. The developed approach is used to examine the effect of sign and magnitude of curvature on the induced anisotropies by altering the rolling direction and diameter of the 'Swiss-roll'. Furthermore, a time-averaged imaging technique based on conventional microscopies (magnetic force microscopy and Kerr microscopy) offers a novel strategy for investigating nanoscale periodic domain wall oscillations and hence dynamic magnetic characteristics of flat and curved structures. This method exploits the benefit of a position-dependent dwell time of periodically oscillating DWs and can determine the trajectory and amplitude of DW oscillation with sub-100 nm resolution. The uniqueness of this technique resides in the ease of the imaging procedure, unlike other DW dynamics imaging methods. The combined understanding of rolling-induced anisotropy and imaging DW oscillation is utilized to examine the dependence of DW dynamics on external stimuli and the structure's physical properties, such as lateral size, film thickness, and curvature-induced anisotropy. The presented methods and fundamental studies help to comprehend the rapidly expanding field of 3-dimensional nanomagnetism and advance high-performance magneto-electronic devices based on self-assembly rolling. |
