Procesos de magnetización en nanocompuestos granulares de ferrita de NiZn/SiO2 y Fe/SiO2

Abstract

En el presente trabajo, se estudió el comportamiento magnético de diferentes sistemas granulares nanoestructurados y los mecanismos de reversión de la magnetización operantes, relacionándolos con la naturaleza, tamaño medio de grano, relativa abundancia de las fases presentes e interacción entre ellas. Dos conjuntos de sistemas magnéticos granulares fueron sintetizados: uno, formado por partículas nanocristalinas de Ni0,5 Zn0,5 Fe2O4 inmersas en una matriz de SiO2, fabricado mediante la técnica de molienda de alta energía y técnicas de química húmeda, como sol-gel e impregnación, y el otro conjunto, consistente de partículas nanocristalinas de óxidos de hierro inmersas, también, en una matriz de SiO2, pero sintetizado por aleado mecánico.

The aim of this work is to study the magnetic behavior of granular nanostructured systems and the involved magnetization reversal mechanisms, relating them with the resulting microstructure. For this purpose, two groups of granular magnetic systems were synthesized. One of them is formed by Ni0,5 Zn0,5 Fe2O4 nanocrystalline particles immersed in a SiO2 matrix synthesized by mechanical alloying and chemical methods, such as sol-gel and wet impregnation techniques. The other group of samples, consisting of nanocrystalline particles of iron oxides also dispersed in a SiO2 matrix, was synthesized by mechanical alloying. From the structural and magnetic characterization, it is found that NiZnFe2O4/SiO2 systems are formed by monodomain particles of NiZn ferrite, having a broad particle-size distribution and a high degree of agglomeration. Such agglomerates of ferrite, strongly coupled by the exchange interaction, are surrounded by the silica phase. The magnetization reversal mechanism operating in these particles is the coherent rotation in all the composites studied, with the exception of those synthesized by the wet impregnation method. In this later case, two reversal modes are acting simultaneously: coherent rotation, for smaller particles, and nucleation and propagation of inverse domains, for those of bigger sizes. For the granular system composed of iron oxides and silica, synthesized by mechanical alloying, the structural and magnetic evolution of the composites during the mechanical milling is studied. The milling process promotes the formation of different iron oxides, resulting in nanocomposites with magnetic properties strongly dependent on the phases formed and their microstructure.