Single step nanocrystallization of FeCuNbSiB/CoPt(Cu) soft/hard magnetic multilayer microwires

Abstract

Nanocrystalline composite FeCuNbSiB/CoPt(Cu) soft/hard magnetic multilayer microwires with controlled magnetic behaviour have been prepared by a single step annealing process. Cu has been used as addition element or as underlayer to the CoPt in a percentage which has been favourable to the reduction of the annealing temperature for the formation of the nanocrystalline state. The suitable choice of the materials used for the soft magnetic nucleus (Finemet) and for the hard deposited layer (Cu doped CoPt or Cu/CoPt system) allowed to tailor the magnetic behaviour by inducing simultaneously ultrasoft and hard nanocrystalline phases in the nucleus and outer layer, respectively, after annealing. The magnetic measurements confirm the formation of two magnetic phases, corresponding to the ultrasoft FeCuNbSiB and hard CoPt-based magnetic materials. A substantial contribution of the hard magnetic phase after the thermal treatment, as a result of the formation of a nanocrystalline structure with a L10 hexagonal phase both in CoPtCu and CoPt/Cu layers with effect on the enhancement of the hard magnetic properties and the development of the bi-phase behaviour has been obtained.