A method, a material system, and the physics for tailoring artificial magnetic field landscapes on micron and submicron length scales over a topographically flat surface in remanence are presented. KeV-He+ ion bombardment induced magnetic patterning was used for the creation of in-plane magnetized domains in Exchange Bias layer systems. This technology sets defined magnetic domain wall charges between the in-plane magnetic domains by individually set domain properties (magnitude and direction of anisotropy parameters) on both sides of the domain wall. The magnetic surface charge distribution was analyzed by magnetic force microscopy and compared to micromagnetic simulations.

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The magnetic modification of exchange bias materials by 'ion bombardment induced magnetic patterning' has been established more than a decade ago. To understand these experimental findings several theoretical models were introduced. Few investigations, however, did focus on magnetic property modifications caused by effects of ion bombardment in the ferromagnetic layer. In the present study, the structural changes occurring under ion bombardment were investigated by Monte-Carlo simulations and in experiments. A strong reduction of the saturation magnetization scaling linearly with increasing ion doses is observed and our findings suggest that it is correlated to the swelling of the layer material based on helium implantation and vacancy creation.

Background: The application of superparamagnetic particles as biomolecular transporters in microfluidic systems for lab-on-a-chip applications crucially depends on the ability to control their motion. One approach for magnetic-particle motion control is the superposition of static magnetic stray field landscapes (MFLs) with dynamically varying external fields. These MFLs may emerge from magnetic domains engineered both in shape and in their local anisotropies. Motion control of smaller beads does necessarily need smaller magnetic patterns, i.e., MFLs varying on smaller lateral scales. The achievable size limit of engineered magnetic domains depends on the magnetic patterning method and on the magnetic anisotropies of the material system. Smallest patterns are expected to be in the range of the domain wall width of the particular material system. To explore these limits a patterning technology is needed with a spatial resolution significantly smaller than the domain wall width. Results: We demonstrate the application of a helium ion microscope with a beam diameter of 8 nm as a mask-less method for local domain patterning of magnetic thin-film systems. For a prototypical in-plane exchange-bias system the domain wall width has been investigated as a function of the angle between unidirectional anisotropy and domain wall. By shrinking the domain size of periodic domain stripes, we analyzed the influence of domain wall overlap on the domain stability. Finally, by changing the geometry of artificial two-dimensional domains, the influence of domain wall overlap and domain wall geometry on the ultimate domain size in the chosen system was analyzed. Conclusion: The application of a helium ion microscope for magnetic patterning has been shown. It allowed for exploring the fundamental limits of domain engineering in an in-plane exchange-bias thin film as a prototypical system. For two-dimensional domains the limit depends on the domain geometry. The relative orientation between domain wall and anisotropy axes is a crucial parameter and therefore influences the achievable minimum domain size dramatically.

A magnetic domain texture has been deterministically engineered in a topographically flat exchange-biased (EB) thin film system. The texture consists of long-range periodically arranged unit cells of four individual domains, characterized by individual anisotropies, individual geometry, and with non-collinear remanent magnetizations. The texture has been engineered by a sequence of light-ion bombardment induced magnetic patterning of the EB layer system. The magnetic texture's in-plane spatial magnetization distribution and the corresponding domain walls have been characterized by scanning electron microscopy with polarization analysis (SEMPA). The influence of magnetic stray fields emerging from neighboring domain walls and the influence of the different anisotropies of the adjacent domains on the Néel type domain wall core's magnetization rotation sense and widths were investigated. It is shown that the usual energy degeneracy of clockwise and counterclockwise rotating magnetization through the walls is revoked, suppressing Bloch lines along the domain wall. Estimates of the domain wall widths for different domain configurations based on material parameters determined by vibrating sample magnetometry were quantitatively compared to the SEMPA data.