Since the pioneering work of Stoner and Wohlfarth over six decades ago, the subject of magnetic behavior of single- (mono)domain particles has held enormous fascination. Magnetization reversal in such monodomain particles occurs often via coherent rotation of spins. As a consequence of this rotation mechanism, magnetic nanoparticles show high coercivities, which lie between soft and hard permanent magnetic materials. The ability to control the magnetism in this type of particles make them very attractive for applications (e.g., particularly in information storage). Moreover, the research on magnetic nanoparticles has shown hopes for the application in the field of biology and medical applications (e.g., drug-targeting, cancer therapy, lymph node imaging, or hyperthermia).

Detailed information on the properties of single-domain nanoparticles is needed before making use of these nanoparticles for any applications. Also the synthesis of such particles by reproducible means is of great importance. The superspins of single-domain particles fluctuate on the timescale modeled by the Néel-Brown theory. The superspins undergo so-called blocking in an ensemble of magnetic nanoparticles with dilute concentration, namely, where interparticle interactions are negligible. However, in dense ensembles interaction effects lead to collective states such as superspin glass behavior or superferromagnetism. Several reports on these subjects as well as on superparamagnetism in the very dilute limit have been made in the last decade. This special issue will focus on the preparation, characterization, structural and magnetic properties, and various possible applications of magnetic nanoparticles. We hope that this will become an important international platform for researchers to summarize the most recent progress and to exchange ideas in the field of magnetic nanoparticles. Potential topics include, but are not limited to:

• Synthesis of magnetic nanoparticles
• Nanoparticle superlattices or supracrystals
• Templated self-organization of nanoparticles
• Superparamagnetism
• Superspin glass behavior
• Superferromagnetism
• Surface spin glass states
• Magnetic core-shell nanoparticles
• Magnetic nanostructures by lithography
• Applications of magnetic nanoparticles
• Simulations and modeling of magnetic nanostructures
• Magnetization dynamics and LLG modeling of magnetic nanoparticles

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