On the origin of remanence enhancement in exchange-uncoupled CoFe_2O_4-based composites

摘要

Abundant efforts are being devoted to the production of nanostructured composites based on ferrites where the exchange-spring mechanism yields larger energy products. However, experimental results occasionally contradict the predictions, and the origin of the phenomenology is not always thoroughly understood. Magnetic properties may eventually evolve in trends similar to that of exchange-spring magnets due to structural changes unrelated to exchange-coupling mechanisms at hard/soft interfaces. Thus, the evaluation of the possible sources of magnetic improvement is pivotal in determining and optimizing the extent of exchange-coupling in spring magnets. Here, we report the observation of remanence improvement and single-phase reversal behavior at room-temperature in CoFe_2O_4/FeCo composites, where the hard and soft phases are predominantly uncoupled. The results are explained in terms of the temperature evolution of the individual properties of CoFe_2O_4. Causes for the observation of single-phase magnetization reversal in exchange-uncoupled systems are discussed. Our results indicate that these type of phenomena must be taken into account in order to thoroughly understand the optimization required to improve the magnetic performance of CoFe_2O_4-based composites.