Nanocrystallization and Surface Magnetic Structure of Ferromagnetic Ribbons and Microwires

The nano-crystals nucleation and growth mechanism in the bulk and at the surface of alloys under the application of a magnetic field or a constant tensile stress during thermal treatment are studied. Clear differences have been found in the nano-crystals growth mechanisms and nano-crystallization of the bulk and surface of the ribbons depending on the treatment in ribbons. The use of a tensile stress is found to activate the nucleation rate, while the use of applied field during thermal annealing produces a completely different effect which does not activate the grain growth in the bulk, but produces ordered arrangements of nano-grains at the surface of the ribbon. In micro-wires the studies show an unusual temperature dependence of the coercive field, consequence of a coexistence of blocked and unblocked particles, and the typical decreasing behaviour of the remanence increasing temperature.