Open Access

Citizen science (CS) can foster transformative impact for science, citizen empowerment and socio-political processes. To unleash this impact, a clearer understanding of its current status and challenges for its development is needed. Using quantitative indicators developed in a collaborative stakeholder process, our study provides a comprehensive overview of the current status of CS in Germany, Austria and Switzerland. Our online survey with 340 responses focused on CS impact through (1) scientific practices, (2) participant learning and empowerment, and (3) socio-political processes. With regard to scientific impact, we found that data quality control is an established component of CS practice, while publication of CS data and results has not yet been achieved by all project coordinators (55%). Key benefits for citizen scientists were the experience of collective impact (“making a difference together with others”) as well as gaining new knowledge. For the citizen scientists’ learning outcomes, different forms of social learning, such as systematic feedback or personal mentoring, were essential. While the majority of respondents attributed an important value to CS for decision-making, only few were confident that CS data were indeed utilized as evidence by decision-makers. Based on these results, we recommend (1) that project coordinators and researchers strengthen scientific impact by fostering data management and publications, (2) that project coordinators and citizen scientists enhance participant impact by promoting social learning opportunities and (3) that project initiators and CS networks foster socio-political impact through early engagement with decision-makers and alignment with ongoing policy processes. In this way, CS can evolve its transformative impact.

In this work, different ferrimagnetic rare-earth-transition-metal heterostructures are investigated. The findings provide implications for future data storage, sensor, and unconventional computing devices. In the first part, ferri- and ferromagnetic films are exchange-coupled and studied as potential composite media for magnetic recording technologies. For this, the underlying individual layers are examined, too. Within this study, the influence of Pd and Pt insertion layers in ferromagnetic Co/Ni multilayers is investigated. In these systems, the maximum effective magnetic anisotropy is more than doubled by the introduced insertion layers, while the initial saturation magnetization and Curie temperature are reduced. Further, amorphous Tb-FeCo alloys and multilayers are studied as the second building block of the desired composite medium. In particular, the structural and magnetic properties are analyzed upon post-annealing. At temperatures above 400 K, irreversible effects on the structural properties are found, which also influence the magnetic properties. It is shown that these changes in properties cannot be prevented by tuning the composition or by a multilayer structure of the film. However, key insights on the structural and magnetic properties upon annealing are provided for future high-temperature devices. Afterward, the exchange-coupled ferrimagnetic/ferromagnetic bilayer is studied. Measurements on the dependency on temperature, the ferrimagnetic composition, and the thickness of the ferromagnet are carried out. Two distinct magnetic reversal mechanisms are revealed. The reversal characteristics depend critically on the thickness of the ferromagnetic layer. The underlying microscopic origin is revealed by high-resolution magnetic force microscopy. Above a certain thickness of the ferromagnet, the switching process is driven by in-plane domain wall propagation. In contrast, thinner ferromagnetic layers exhibit a nucleation-dominated reversal due to grain-to-grain variations in magnetic anisotropy. Although the realization of an exchange-coupled composite medium for magnetic recording can not be achieved, insights for the future realization of sub micron high energy density permanent magnets and spintronic devices are gained. In the second part of this work, topologically protected spin structures, including skyrmions and antiskyrmions, are investigated in Fe/Gd-based multilayers. Particularly in coexisting phases, different topologically protected magnetic quasi-particles may show fascinating physics and potential for spintronic devices. While skyrmions are observed in a wide range of materials, until now, antiskyrmions have been exclusive to materials with D2d or S4 symmetry. In this work, first and second-order antiskyrmions are stabilized for the first time by magnetic dipole-dipole interaction. Using Lorentz transmission electron microscopy imaging, coexisting first- and second-order antiskyrmions, Bloch skyrmions, and type-2 bubbles are observed, and the range of material properties and magnetic fields where the different spin objects form and dissipate is determined. The discovered phase pocket of metastable antiskyrmions for low saturation magnetization and uniaxial magnetic anisotropy values is confirmed by micromagnetic simulations and represents a recipe, which has to be satisfied for the stabilization of antiskyrmions by dipole-dipole interaction in other material systems. Furthermore, the nucleation process of the spin objects and the influence of an in-plane magnetic field are studied. Additionally, post-deposition techniques are employed to locally change the anisotropy of the samples and influence the nucleation and stability range of the spin objects. The gained knowledge significantly simplifies future investigations of antiskyrmions. Moreover, the coexisting phases of different topologically protected spin objects and their controlled nucleation provide great potential for further studies on magnetic quasi-particle interactions, spin dynamics, as well as for possible future applications in spintronics, namely the racetrack memory, skyrmionic interconnections, skyrmion-based unconventional computing, and sensor devices.