Functionalized Nanomagnets: Perspectives in Materials Science and Medicine
Michael Farle (Universität Duisburg-Essen)

Let’s dream of materials that convert energy reversibly by temperature changes between day and night or provide a non-invasive treatment of cancer. These visions may be realized by using magnetic nanoparticles that are functionalized to be biocompatible or environmentally stable and recyclable, which are low-cost and allow the design of self-healing materials.
Starting with a discussion of basic concepts of magnetic properties with a focus on how to tune parameters in a nanomagnet, I will highlight selected state-of-the-art experimental approaches [1,2] that allow us to experimentally analyze multifunctional particles with single particle or even atomic precision. The apparently complex behavior of hybrid metal/metal, metal/oxide, or oxide/oxide interface materials –core-shell materials - can be understood from the three fundamental interactions in magnetism: magnetic exchange due to orbital overlap, spin-orbit interaction due to inner- and intra-atomic relativistic effects (e.g., crystal field effects) and the long-range magnetic dipolar interaction. Several examples will be presented, including the formation of above-room-temperature ferromagnetic interface layers between core/shell antiferromagnetic shells, the design of a macroscopic magnet with a monopole-like magnetic response [3] and the first magnonic dispersion measured in single magnetotactic bacteria.
Work supported by European Union and Deutsche Forschungsgemeinschaft. The fruitful collaboration with many colleagues and students is thankfully acknowledged.
[1] M. Farle Imaging techniques: Nanoparticles atoms pinpointed NATURE (News and Views) 542 (2017) 35
[2] Zi-An Li, et al. Magnetic Skyrmion Formation at Lattice Defects and Grain Boundaries Studied by Quantitative Off-Axis Electron Holography, Nano Lett. 17 (2017) 1395–1401, and Nat. Comm. 8 (2017) 15569
[3] Franziska Scheibel, Detlef Spoddig, Ralf Meckenstock, Aslı Çakır, Michael Farle, and Mehmet Acet Shell-ferromagnetism in a Ni-Mn-In off-stoichiometric Heusler studied by ferromagnetic resonance AIP Advances 7 (2016) 056425