Geometric-magnetic chirality coupling in double-helix nanostructures

Abstract

Artificial double-helix ferromagnetic nanostructures combine a chiral geometry and competing exchange/dipolar inter-strand coupling [1]. Additionally, the geometrical control of magnetic chirality enables the connection of spin states with opposite magnetic chirality through chirality interfaces. All this results in a rich and tuneable magnetic platform to study chiral effects in three dimensions, including the imprinting of chiral 3D spin textures [1], and of stray fields with topological features [2]. In this contribution, we will present XMCD ptychography imaging experiments in these systems under external magnetic fields [3]. First, we will show how we can fabricate and finely tune the geometry and magnetic material of these nanostructures thanks to “f3ast”, our open-access 3D nano-print software for focused electron beam induced deposition [4]. Secondly, we will show how the application of fields during a major hysteresis loop leads to the formation of two interfaced helical-vortex states at remanence, which demonstrate the coupling between geometrical and magnetic chirality. Finally, we will show how under particular field sequences, it is possible to magnetically reconfigure the system and break the geometrical-magnetic coupling. Under these conditions, we observe the formation of a single helical-vortex tube at remanence extending along the entire system, and we can follow its evolution under applied magnetic fields. We will discuss the different topology of the two distinct states identified, as well as possible applications of 3D magnetic interconnectors with reconfigurable topological spin states [5].