Synthesis and magnetic properties of FeNi<Subscript>3</Subscript>/Al<Subscript>2</Subscript>O<Subscript>3</Subscript> core-shell nanocomposites

In this study, FeNi<Subscript>3</Subscript>/Al<Subscript>2</Subscript>O<Subscript>3</Subs cript> core-shell nanocomposites, where individual FeNi<Subscript>3</Subscript> nanoparticles were coated with a thin layer of alumina, were fabricated by a modified sol-gel method. Several physical characterizations were performed on the samples of FeNi<Subscript>3</Subscript>/Al<Subscript>2</Subscript>O<Subscript>3</Subs cript> nanocomposites with different thickness of Al<Subscript>2</Subscript>O<Subscript>3</Subscript> shell. The encapsulation of FeNi<Subscript>3</Subscript> nanoparticles with alumina stops FeNi<Subscript>3</Subscript> agglomeration during heat treatment, and prevents interaction among the closely spaced magnetic FeNi<Subscript>3</Subscript> nanoparticles. The Al<Subscript>2</Subscript>O<Subscript>3</Subscript> insulating shell improves the soft magnetic properties of FeNi<Subscript>3</Subscript>. The study of the complex permeability of the samples shows that the real part μ’ of the permeability of the sample with Al molar content of 20% (Al/(Fe+Ni)) is as high as 12, and independent of frequency up to at least 1 GHz. The tunneling magnetoresistance arising from the presence of the Al<Subscript>2</Subscript>O<Subscript>3</Subscript> shell have also been studied. Copyright EDP Sciences/Società Italiana di Fisica/Springer-Verlag 2005