Clocked dynamics in artificial spin ice.

Artificial spin ice (ASI) are nanomagnetic metamaterials with a wide range of emergent properties. Through local interactions, the magnetization of the nanomagnets self-organize into extended magnetic domains. However, controlling when, where and how domains change has proven difficult, yet is crucial for technological applications. Here, we introduce astroid clocking, which offers significant control of ASI dynamics in both time and space. Astroid clocking unlocks a discrete, step-wise and gradual dynamical process within the metamaterial. Notably, our method employs global fields to selectively manipulate local features within the ASI. Sequences of these clock fields drive domain dynamics. We demonstrate, experimentally and in simulations, how astroid clocking of pinwheel ASI enables ferromagnetic domains to be gradually grown or reversed at will. Richer dynamics arise when the clock protocol allows both growth and reversal to occur simultaneously. With astroid clocking, complex spatio-temporal behaviors of magnetic metamaterials become easily controllable with high fidelity.

Tailoring Spin Textures in Complex Oxide Micromagnets.

Engineered topological spin textures with submicron dimensions in magnetic materials have emerged in recent years as the building blocks for various spin-based memory devices. Examples of these magnetic configurations include magnetic skyrmions, vortices, and domain walls. Here, we show the ability to control and characterize the evolution of spin textures in complex oxide micromagnets as a function of temperature through the delicate balance of fundamental materials parameters, micromagnet geometries, and epitaxial strain. These results demonstrate that in order to fully describe the observed spin textures, it is necessary to account for the spatial variation of the magnetic parameters within the micromagnet. This study provides the framework to accurately characterize such structures, leading to efficient design of spin-based memory devices based on complex oxide thin films.

Spin-flop coupling and exchange bias in embedded complex oxide micromagnets.

The magnetic domains of embedded micromagnets with 2 µm×2 µm dimensions defined in epitaxial La0.7Sr0.3MnO3 (LSMO) thin films and LaFeO3/LSMO bilayers were investigated using soft x-ray magnetic microscopy. Square micromagnets aligned with their edges parallel to the easy axes of LSMO provide an ideal experimental geometry for probing the influence of interface exchange coupling on the magnetic domain patterns. The observation of unique domain patterns not reported for ferromagnetic metal microstructures, namely divergent antiferromagnetic vortex domains and "Z"-type domains, suggests the simultaneous presence of spin-flop coupling and local exchange bias in this system.

Crossover from spin-flop coupling to collinear spin alignment in antiferromagnetic/ferromagnetic nanostructures.

The technologically important exchange coupling in antiferromagnetic/ferromagnetic bilayers is investigated for embedded nanostructures defined in a LaFeO(3)/La(0.7)Sr(0.3)MnO(3) bilayer. Exploiting the element specificity of soft X-ray spectromicroscopy, we selectively probe the magnetic order in the two layers. A transition from perpendicular to parallel spin alignment is observed for these nanostructures, dependent on size and crystalline orientation. The results show that shape-induced anisotropy in the antiferromagnet can override the interface exchange coupling in spin-flop coupled nanostructures.

Antiferromagnetic domain reconfiguration in embedded LaFeO3 thin film nanostructures.

Using photoemission electron microscopy in combination with X-ray magnetic linear dichroism, we report reconfiguration upon nanostructuring of the antiferromagnetic domain structure in epitaxial LaFeO3 thin films. Antiferromagnetic (AFM) nanoislands were synthesized using a dedicated process, devised to define nanostructures with magnetic order embedded in a paramagnetic matrix. Significant impact on the AFM domain configuration was observed. Extended domains were found to form along edges parallel to the in-plane <100> crystalline axes of the cubic substrate, with their AFM spin axis parallel to the edge. No such edge-imposed domain configuration was found for nanoislands defined with the edges at 45° with the in-plane crystalline axes. Epitaxial constraints on the film crystalline structure appear to play an important role in the formation of the edge-bound extended AFM domains. The data indicate a magnetostatic origin of this domain reconfiguration.