Interfacial exchange coupling is known to improve the permanent magnetic performance (i.e., maximal energy product) in composites of magnetically hard and soft particles. The prevailing strategy, employed in a plethora of compositions, consists in maximizing the coupling between the hard and soft phases and optimizing material parameters such as particle size or phase composition. In CoFe2O4-FeCo nanocomposites, it is experimentally shown that interparticle uncoupling in combination with the sizes of the soft phase grains below the single-domain threshold leads to enhanced magnetic properties at room temperature, while maximizing exchange coupling implies a collapse in coercivity and hence in the maximal energy product. The results are corroborated by micromagnetic calculations and the origin of the exchange-induced softening is discussed. It is emphasized that engineering interfaces in order to optimize, rather than maximize, the degree of exchange coupling are a necessary requirement to improve the energy product in nanocomposite magnets and to successfully develop advanced rare-earth-free permanent magnets.
Energy Product Enhancement in Imperfectly Exchange-Coupled Nanocomposite Magnets
Bertoni G;de Julian Fernandez C;Sangregorio C;
2016
Abstract
Interfacial exchange coupling is known to improve the permanent magnetic performance (i.e., maximal energy product) in composites of magnetically hard and soft particles. The prevailing strategy, employed in a plethora of compositions, consists in maximizing the coupling between the hard and soft phases and optimizing material parameters such as particle size or phase composition. In CoFe2O4-FeCo nanocomposites, it is experimentally shown that interparticle uncoupling in combination with the sizes of the soft phase grains below the single-domain threshold leads to enhanced magnetic properties at room temperature, while maximizing exchange coupling implies a collapse in coercivity and hence in the maximal energy product. The results are corroborated by micromagnetic calculations and the origin of the exchange-induced softening is discussed. It is emphasized that engineering interfaces in order to optimize, rather than maximize, the degree of exchange coupling are a necessary requirement to improve the energy product in nanocomposite magnets and to successfully develop advanced rare-earth-free permanent magnets.I documenti in IRIS sono protetti da copyright e tutti i diritti sono riservati, salvo diversa indicazione.