Citation: Constantinescu, C.-D.; Petrescu, L.-G. Magnetic Materials, Thin Films and Nanostructures. Magnetochemistry 2023, 9, 133. https://doi.org/10.3390/ magnetochemistry9050133 Received: 5 May 2023 Revised: 12 May 2023 Accepted: 16 May 2023 Published: 19 May 2023 Copyright: © 2023 by the authors. Licensee MDPI, Basel, Switzerland. This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY) license (https:// creativecommons.org/licenses/by/ 4.0/). magnetochemistry Editorial Magnetic Materials, Thin Films and Nanostructures Catalin-Daniel Constantinescu 1, * and Lucian-Gabriel Petrescu 2, * 1 CNRS, University Aix-Marseille, LP3/UMR 7341 (Laboratoire “Lasers, Plasmas et Procédés Photoniques), Campus de Luminy, F-13009 Marseille, France 2 UPB—University “Politehnica” of Bucharest, Faculty of Electrical Engineering, “Technical and Applied Magnetism” Laboratory, RO-060042 Bucharest, Romania * Correspondence: catalin.constantinescu@cnrs.fr (C.-D.C.); lucian.petrescu@upb.ro (L.-G.P.) Abstract: In this first volume, we cover relevant aspects of chemical and physical processes of the production and characterization of magnetic materials in bulk, thin films, nanostructures, and/or nanocomposites, as well as modeling aspects involving such structures. Accordingly, this volume presents eleven original research and review works on the challenges and trends covering funda- mental and experimental work, with a special focus on the design, synthesis, and characterization of various types of magnetic materials, and the study of their structure–property relationships. State-of- the-art results on the development of new experimental concepts, leading to the transfer, chemical transformation, and high-resolution patterning of advanced thin films and nanomaterials, and to the design and fabrication of devices, are also presented and discussed. Keywords: magnetism; nanomaterials; nanostructures; nanoparticles; thin films; electromagnetic shielding; magnetotransport; single-molecule-magnets; magnetic shape memory polymers; magnetic soft materials Ever since antiquity, there have been legends circulating about the phenomenon that we generally call today “magnetism”. The best known is of a young shepherd from the island of Crete, named Magnes [1]. At one point in his life, while tending the sheep on Mount Ida, he noticed that the metal part of the sole and the nails of his boots were attracted to the ground on which he was treading. To find out what was going on, he began to dig, revealing a strange earth-black stone: a piece of lodestone, or “magnetite”. Magnetite is a natural ferrite exhibiting magnetic properties. Today, we know that is a stoichiometric mixed oxide consisting of FeO and Fe 2 O 3 , with the chemical formula Fe 3 O 4 , and its structure is of the “spinel” type. It is a “ferrimagnetic” material, and its Curie temperature is 858 K. Just to exemplify for the reader the importance of this mineral, the strongest natural magnet: it is critical in the understanding and evolution of terrestrial paleomagnetism, in the formation and evolution of rocks, and other areas [2]. Of course, observations of such phenomena have been made long before the appear- ance of the first forms of writing [3], so we cannot rely on such legends. This story might be apocryphal, but in this case, there are many similarities with historic reality, the most important being that the empirical discovery of magnetism and its mention was made by the Greeks, Indians, and Chinese through observing the properties of the rocks that contained the magnetite mineral [4]. Pliny the Elder (23–79 CE) himself wrote about a hill, somewhere on the banks of the Indus River, which was apparently made entirely of something mysterious that attracted iron. The inexplicable nature of magnetic attraction has been exploited over time by storytellers, meaning it has become difficult to separate truth from fiction. It was believed for a long time that there were islands that were com- pletely made up of magnetite and that, by virtue of the “special” properties of this mineral that is part of some rocks, could attract ships to the shore (they contained nails and iron beams in their structure). One of the explanations for the disappearances of the ships was that they had been destroyed on impact with such magnetic islands—a kind of ancient Magnetochemistry 2023, 9, 133. https://doi.org/10.3390/magnetochemistry9050133 https://www.mdpi.com/journal/magnetochemistry