Professor Thorsten Hesjedal FInstP

Abstract:

Magnetic devices have shown the potential to be used not only as storage elements but also as nonvolatile and programmable logic devices. We present a magnetic logic device element-the S state element-that consists of a single magnetic layer. Its output can be controlled by orthogonal magnetic inputs. The reconfigurable logic element can be easily integrated with common magnetoresistive device concepts, such as spin valves or magnetic tunnel junctions. Using Permalloy as an example, we demonstrate the feasibility of magnetologic operation through micromagnetic simulations. © 2010 American Institute of Physics.

Abstract:

Elastic properties of nanoscopic materials, structures and thin films are important parameters controlling their growth, as well as their optical and electronic properties. Acoustic microscopy is a well-established method for elastic imaging. In order to overcome its micrometer-scale diffraction-limited lateral resolution, scanning probe microscopy-based acoustic near-field techniques have been developed. Among the acoustic modes used for microscopy, surface acoustic waves (SAWs) are especially suited for probing very small and thin objects due to their localization in the vicinity of the surface. Moreover, the study of SAWs is crucial for the design of frequency filter devices as well as for fundamental physical studies, for instance, the probing of composite fermions in two-dimensional electron systems. This review discusses the capabilities and limitations of SAW-based scanning probe microscopy techniques. Particular emphasis is laid on the review of surface acoustic waves and their interaction with elastic inhomogeneities. Scattering, diffraction and wave localization phenomena will be discussed in detail. Finally, the possibilities for quantitative acoustic microscopy of objects on the nanoscale, as well as practical applications, are presented. © 2010 IOP Publishing Ltd.

Abstract:

The magnetic domain structure of MnAs stripes exhibits a number of domain transitions that are inclined with respect to the system's easy axis. Among them are laterally confined slanted and V-shaped domain walls, as well as extended zigzag shaped transitions that are running along the stripe axis. The nature of these unusual domain transitions was investigated with the help of micromagnetic simulations and compared with experimental magnetic force microscopy (MFM) images. All types of inclined walls result from the underlying three-dimensional domain structure of the wires. In the domain transition region, the underlying flux closure pattern gets asymmetrically distorted in the cross-sectional wire plane as the system changes its domain types. The results of the simulations are in excellent qualitative agreement with the stray field patterns observed with MFM. © 2009 American Institute of Physics.