Dear Colleagues,

Producing and handling nm- to µm-scale magnetic particles has been brought to a high degree of perfection over the last two decades. The surface functionalization and the specific attachment of biomolecules to magnetic particles have also advanced through state-of-the-art surface chemistry and biochemical linking system.

Meanwhile, a competition has been established worldwide to realize magnetic nanoparticles through either a bottom-up or a top-down approach. The bottom-up approach has produced some nice results such as core-shell nanoparticles or interesting morphologies such as star-shaped magnetite particles. Recently, a new bottom-up preparation method for magnetic nanoparticles and complex structures has attracted attention because it is based on focused electron beam induced deposition, a direct writing method for the fabrication of nanostructures whose lateral resolution can compete with that of advanced electron-beam lithography. The top-down approach is usually based on multilayer systems, which are then produced into micro- or nanostructures using e-beam lithography strategies. In contrast to the alternative, the bottom-up approach, in which nanoparticles are synthesized by chemical bonding of atoms, the top-down approach has the charm of integrating complex magnetic interactions into the multilayer systems and, thus, also into the resulting nanostructures. On the other hand, especially in ternary or quaternary alloy systems, starting from multilayer systems, the composition responsible for the physical properties can be transferred very precisely into the resulting micro- or nanostructures.

Spinels and Heusler alloys have also been added to simple material systems, such as cobalt phases or the Fe oxides, which were initially the focus of research. The Heusler alloys, especially, have high magnetizations and small magnetocrystalline anisotropies, and, thus, shift the superparamagnetic limit to larger particle diameters with simultaneously higher magnetic moments.

This Special Issue will assess the currently realizable particle and bead properties along both preparation avenues with resulting magnetization, magnetic moment, and superparamagnetic limits in the range from about 10 nm to 1 mm. The governing questions to be answered are how small and reliable can magnetic nanoparticles be produced? What is the yield of the respective production method? Are there alloys with very special properties? How fast, precise, and efficient can these nanoparticles or beads be transported into microfluidic systems? How large is the expected magnetic interaction with magnetoresistive sensors? How easily can these nanoparticles or beads be functionalized? Are new applications as functions of nanoparticles or bead size in sight?

Consequently, this Special Issue will cover a wide range of topics ranging from the simulation-based design, fabrication, and characterization of magnetic nanoparticles or beads, their interaction with magnetoresistive sensors, and the prediction of new applications.

Prof. Dr. Andreas Hütten
Guest Editor

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• Simulation-based design magnetic nanoparticles or beads
• Top-down and bottom-up fabrication of magnetic nanoparticles or beads
• Yield of fabrication methods, extended superparamagnetic limit
• Interaction range with magnetoresistive sensors
• Prediction of new applications