Towards ferrite based rare-earth free permanent magnets: from model systems to new technological applications

Resumen

Permanent magnets are essential in many applications of very relevant technological areas (transport, communications technology, energy) and are present in virtually all smart devices. However, they are not without controversy and have generated in recent years serious economic and political problems, as well as having important repercussions on the environment. In 2012 the global alarm was raised due to the monopoly derived from the strategic geographical situation of the so-called rare earths, fundamental constituent elements of these materials. Advances in nanoscience and nanotechnology are key in the search for alternatives to permanent magnets based on rare earths. In this sense, and in a general way, this thesis work combines fundamental studies in nanomagnetism with energetically efficient technological processes in order to be able to develop permanent magnets free of competitive rare earth of last generation, as well as to implement new technological applications. To this end, the objectives set out in the present study have included: 1) The study of rare earth-free magnetic systems exploiting anisotropy, shape and microstructure in both model systems (epitaxial layers and manganese nanowires) and in isotropic ferrite powders. 2) The search for general relations to improve / enhance the magnetic properties of rare earthfree materials based on nanostructured ferrites by effective, reproducible and scalable methods. 3) Understanding and controlling the microstructural effects on the magnetic properties of treated and refined ferrite isotropic powders. 4) The development of new methodologies to enhance the properties of permanent magnets based on isotropic ferrite powder, and the prototyping of new applications making use of the permanent magnets free of developed rare earths. From the scientific point of view, it is necessary to highlight the microscopic determination of the magnetization reversal processes in model systems as well as the experimental demonstration of the generic effects induced by engineered microstructure (tensions and grain size) on the magnetic properties in processed isotropic powders. From the technological point of view, to review the development of an efficient, reproducible and scalable methodology to produce isotropic powder with improved magnetic properties (coercivity and / or (BH)max product) as well as the design and prototyping of new technological applications..