Magnetic properties of stress/field annealed nanocrystalline FeCoNbB alloys

Amorphous CoxFe84-xNb7B9 (21 less than or equal to x less than or equal to 33) ribbons were prepared by the planar how casting. The samples were annealed at the temperatures 550 degrees C and 600 degrees C with magnetic field of 400 kA/m applied in the plane of the ribbon transversally to the ribbon axis. Tensile stress sigma(a) ranging from 0 to 150 MPa was applied along the ribbon length. From the analysis of the hysteresis loops and Delta E-effect measurements it can be concluded that the stress/field-induced anisotropy results from a competition of two contributions. The type and magnitude of anisotropy can be controlled by the stress applied during annealing. The transversal anisotropy induced by the field-only annealing changes to the longitudinal one when the applied stress increases. The change of anisotropy easy direction at oo is well displayed by the dependence of magnetic properties on sigma(a). The best nanocrystalline samples exhibit H-c as low as 4 A/m and Delta E-effect above 50%. (C) 1999 Elsevier Science B.V. All rights reserved.