Evolution of physical properties of amorphous Fe-Ni-Nb-B alloys with different Ni/Fe ratio upon thermal treatment

Amorphous ribbons (Fe-Ni)(81)Nb(7)B(12) with Ni/Fe = 0, 1/6, 1/3 and 1 were prepared by planar flow casting. Thermal treatment of samples was performed in vacuum at temperatures chosen to map the evolution of selected properties in the course of transformation from amorphous state. The coefficient of thermal dilatation exhibits changes at temperatures close to the glass transition, Curie and crystallization temperatures; these effects are enhanced or suppressed by cyclic thermal treatments up to the vicinity of these temperatures. The values of saturation magnetostriction lambda(S) allow to infer about processes taking place in the investigated materials, especially with respect to formation of new magnetic phases or magnetic anisotropy. Complex processes of structural transformations induced by thermal treatment are strongly affected by Ni percentage. A transitional, magnetically harder phase, which is formed at lower temperatures preferentially near surfaces of the Ni-richest alloy, produces characteristic hysteresis loop shape. This shape disappears after annealing at higher temperatures and enables the material to show the lowest coercivity of the whole alloy series. The saturation magnetic polarization reflects mainly the resulting Curie temperature, which falls with increasing Ni percentage. Magnetic hysteresis loops were also used in the study of dynamics of magnetic domains by MOKE. Domain shape evolution is shown in dependence on composition and thermal treatment as well as a function of applied magnetic field, ranging from remanent sample state to magnetic saturation. (C) 2010 Elsevier B.V. All rights reserved.