The huge influence of nanograins on the magnetic properties of iron-based Fe-Cu-Nb-B nanocrystalline alloys

In 1995 Skorvanek and O'Handley presented the first experimental evidence for a huge influence of nanograins on the magnetization of a nanostructured alloy. In this contribution experiments are described, performed on as-cast amorphous and nanostructured Fe79Cu1Nb7B13 alloys. In order to get nanostructured samples with different nanograin contents the samples were annealed at different properly chosen temperatures in vacuum. This led to the formation of nanograins embedded in a residual amorphous matrix. These nanograins consist of pure bcc Fe of about 5-6 nm in diameter. Their content can be enhanced without markedly changing their size when annealing at slightly higher temperatures. So an alloy series with the same nominal composition but different nanograin contents and residual amorphous matrices, i.e. a series of nanostructured alloys, was obtained. Our aim was to study the influence of increasing nanograin concentration on the magnetic properties of the coupled system amorphous matrix plus nanograins. We describe magnetization measurements over a wide temperature range, below and above the Curie temperature of the initial amorphous matrix. In a next step these measurements are evaluated in a molecular field approach assuming two different coupled ferromagnetic systems assigned to the amorphous matrix and the nanograins