P. Kwapuliński

Optimization of soft magnetic properties in nanoperm type alloys

Abstract In the present paper, it was shown that soft magnetic properties of the group of amorphous alloys Fe–X2–B22 (X=Cr, Zr and Nb) can be optimized (magnetic permeability increases about five times) by applying 1-h annealing at temperatures: 600, 600, 650 and 700 K for the Fe78B22, Fe76Cr2B22, Fe76Zr2B22 and Fe76Nb2B22 alloys, respectively. This effect is attributed to annealing out of free volumes formed into material during fabrication and for the Fe76Zr2B22 alloy also to a formation of a nanocrystalline phase. Using isothermal measurements of magnetization (magnetic balance), it was shown that the process of formation of nanocrysalline phase can be described by Johnson–Mhel–Avrami kinetic. Activation enthalpy of this process was deduced as 3.2 eV and the power law exponent 3.4.

Nanocrystallisation of amorphous alloys based on iron

Abstract In the present paper, the FeCu1–X–Si13B9 alloys (X=Zr, Cr) were investigated by making use of different experimental techniques: X-ray diffraction, HREM, magnetic and electric measurements (permeability, coercive field, magnetisation, electrical resistivity). It is shown that soft magnetic properties of all examined alloys can be optimised by applying well-defined thermal annealing (magnetic permeability increases more than 20 times). This effect can be attributed to the formation of a nanocrystalline phase αFe(Si) with a mean grain size from 10 to 30 nm. The optimisation annealing temperature depends on the atomic radius of the alloying additions. In the case of the Fe74Cu1Cr1Zr2Si13B9 alloy, interaction of Zr and Cr atoms causes an increase of 1-h optimisation annealing temperature Tap of more than 200 K compared to Tap of Fe74Cu1Cr3Si13B9.

Optimisation of soft magnetic properties in Fe–Cu–X–Si13B9 (X=Cr, Mo, Zr) amorphous alloys

Abstract In the present paper a group of Fe–Cu–X–Si 13 B 9 (X=Cr, Mo, Zr) amorphous alloys has been examined by applying different experimental techniques—magnetic permeability, magnetic after-effect, coercive force and electrical resistivity measurements. It has been shown that their soft magnetic properties can be optimised by 1-h thermal annealing at the temperature close to the crystallisation temperature. This leads to an increase of permeability and a decrease of coercive force, thermal instability (magnetic after-effect intensity) and electrical resistivity of the material. The optimisation effect is discussed in terms of different processes—(i) a formation of a nanocrystalline phase with the grain size much smaller than the ferromagnetic exchange length, (ii) an annealing out of microvoids formed during the fabrication process and also (iii) a decrease of the effective magnetostriction constant. The temperature of optimisation annealing treatment is always higher than the Curie temperatures of the materials and varies approximately linearly with the atomic radius of the alloying additions.

Magnetic properties of Fe74Cu1CrxZr3−xSi13B9 amorphous alloys

Abstract Optimisation of soft magnetic properties in the Fe 74 Cu 1 Cr x Zr 3− x Si 13 B 9 group of amorphous alloys has been examined by applying different experimental techniques. It has been shown that 1-h annealing treatment at elevated temperatures leads to a significant increase of magnetic permeability determined at room temperature. This effect has been attributed to annealing out of microvoids and to formation of nanocrystalline phase.