Engineering topics

Stopfel, Henry

Publications and source records attributed to Stopfel, Henry.

3 records

DOE OSTI2019

The influence of diameter on the magnetic saturation in Fe 84 Cu 16 /MgO [0 0 1] multilayered islands

The saturation field of circular islands, consisting of Fe 84 Cu 16 [/MgO] 9 Fe 84 Cu 16 multilayers, increases with decreasing diameter of the islands. When the diameter of the islands is below 450 nm the field induced changes are dominated by a coherent rotation of the moment of the Fe 84 Cu 16 layers. For diameters of 2 μm and larger, a signature of domain nucleation and evolution is observed. Here, the changes in the saturation field with diameter of the islands are ascribed to the interplay between interlayer exchange coupling, stray field coupling at the edges and the crystalline anisotropy of the Fe 84 Cu 16 layers.

77 NANOSCIENCE AND NANOTECHNOLOGY↗

DOE OSTI2018

Magnetic order and energy-scale hierarchy in artificial spin-ice structures

In order to explain and predict the properties of many physical systems, it is essential to understand the interplay of different energy scales. Here we present investigations of the magnetic order in thermalized artificial spin-ice structures, with different activation energies of the interacting Ising-like elements. We image the thermally equilibrated magnetic states of the nanostructures using synchrotron-based magnetic microscopy. By comparing results obtained from structures with one or two different activation energies, we demonstrate a clear impact on the resulting magnetic order. The differences are obtained by the analysis of the magnetic spin structure factors, in which the role of the activation energies is manifested by distinct short-range order. Furthermore, these results highlight the potential of artificial spin-ice structures to serve as model systems for designing various energy-scale hierarchies and investigating their impact on the collective dynamics and magnetic order.

77 NANOSCIENCE AND NANOTECHNOLOGY↗

DOE OSTI2018

Interaction modifiers in artificial spin ices

The modification of geometry and interactions in two-dimensional magnetic nanosystems has enabled a range of studies addressing the magnetic order, collective low-energy dynamics and emergent magnetic properties in, for example, artificial spin-ice structures. The common denominator of all these investigations is the use of Ising-like mesospins as building blocks, in the form of elongated magnetic islands. Here, we introduce a new approach: single interaction modifiers, using slave mesospins in the form of discs, within which the mesospin is free to rotate in the disc plane1. We show that by placing these on the vertices of square artificial spin-ice arrays and varying their diameter, it is possible to tailor the strength and the ratio of the interaction energies. We demonstrate the existence of degenerate ice-rule-obeying states in square artificial spin-ice structures, enabling the exploration of thermal dynamics in a spin-liquid manifold. Furthermore, we even observe the emergence of flux lattices on larger length scales, when the energy landscape of the vertices is reversed. In conclusion, the work highlights the potential of a design strategy for two-dimensional magnetic nano-architectures, through which mixed dimensionality of mesospins can be used to promote thermally emergent mesoscale magnetic states.

77 NANOSCIENCE AND NANOTECHNOLOGY↗