2018 - Sustainable Industrial Processing Summit & Exhibition
4-7 November 2018, Rio Othon Palace, Rio De Janeiro, Brazil
| Magnetic Materials - Physics and Future Aspects Roland Groessinger1; 1VIENNA UNIVERSITY OF TECHNOLOGY, FACULTY OF PHYSICS, Wien, Austria; PAPER: 274/SISAM/Keynote (Poster) POSTER ABSTRACT: All magnetically ordered materials exhibit a quantum-mechanic mediated exchange between the electron spins of neighbouring atoms: this means that the electronic structure plays the dominant role. In the case of metallic systems, most important are the 3d-metals and alloys, where the band structure of the 3d-electrons and the position of the Fermi level with respect to the spin-up and down electrons determine the state and magnitude of magnetic ordering. This phenomenon is also responsible for the large magnetic moment in metallic 3d-systems (about 2.2 μB) [1]. Due to the strong direct exchange between the 3d-electrons, most of these metals or alloys exhibit a magnetic ordering temperature above room temperature, which makes them invaluably important for modern techniques. For practical applications, extrinsic properties such as the microstructure essentially determines the magnetic behaviour, especially the shape of the hysteresis loop, and consequently the losses. Examples here are Fe-Si alloys (transformers, generators etc) or new systems such as amorphous and nanocrystalline alloys. In nanocrystalline alloys, where the exchange coupling acts over the grain boundaries, this way reducing the anisotropy and consequently the coercivity [2]. The other important group of magnetic elements are the rare earths (La,...Gd,...Lu). There, the effect of the crystal electrical field on the 4f levels and the coupling between the 4f moments (orbital moment L) on the crystallographic axis, causes high magnetocrystalline anisotropies and/or high values of magnetostriction [3]. Therefore, nowadays, alloys between 4f-elements and 3d-elements are used for providing not only high-quality permanent magnets (such as Sm-Co or Nd-Fe-B) but also high- magnetostrictive systems (such as (Tb,Dy)-Fe). Within this presentation, the fundamental aspects of magnetism — which limits also the achievable magnetization density — are summarised and discussed. Some aspects of the future development in different magnetic materials will also be discussed. References: [1] Magnetic Properties of Metals; Group III, Vol 19 (Landolt-Börnstein); Chapt. 7.1.2.3 [2] Herzer, G; Nanocrystalline Soft Magnetic Materials, Physica Scripta 1993, T 49: 307 [3] Clark AE; IEEE Trans Magn. 21 (1985) 1945-47 |
