ANNUAL REPORT - MTA SzFKI

I. METALLURGY AND MAGNETISM
L.K. Varga, I. Balogh, É. Fazakas # , P. Kamasa, G. Konczos, Gy. Kovács + , J. Pádár, L.
Pogány, F.I. Tóth
Metallurgy. — The bulk glass forming ability (GFA) of Cu-based alloys have been
studied in collaboration with the Materials Science Department of Miskolc University,
Hungary. Several compositions have been prepared, following the bulk GFA criteria
published so far in the literature, such as Cu 100-x-y-z Zr x Ti y Ag z , Cu 100-x Mm x Al y where Mm
means Mischmetal.
Surveying all the Cu-based amorphous alloys published in the literature so far, it turned
out that the atomic mismatch condition of Egami and Waseda is fulfilled for all the Cubased
bulk amorphous alloys, the λ value being above 0,3. Combining the chemical
coordinates of Miedema (y) with the atomic mismatch (x), the glass forming and non-glass
forming regions were found separated by the following curve: y=|10|∆Φ * |-39 |∆(1/n ws 1/3 |-1|
and x=|1-R x /R Cu | for the binary Cu-based alloys.
The glass forming ability of Al-based alloys (mainly of Al 85 Mm 5 Ni 8 Co 2 type
compositions) has been investigated during the compaction of powders obtained by gas
atomising and chopping the rapidly quenched ribbons.
Soft magnetic nanocrystalline alloys. — Based on a Quasi-DC hysterograph, an
experimental technique has been developed to obtain the true “static” hysteresis curve.
This is the so-called “ballistic “method to obtain the hysteresis loop by integrating the
measured incremental permeability (µ incremental = µ diff ) versus biasing DC field, H DC . In
addition, it was demonstrated that it is possible to decompose the quasi-static hysteresis
loop into two contributions deriving from domain magnetization rotation (DR) and domain
wall movement (DWM) (Fig. 1 and Fig. 2) and this decompositon was modelled
theoretically by the hyperbolic T model. The hyperbolic T model was further improved by
splitting it in 3 overlapping hysteretic contributions: one DR and two DWM (jumping and
annihilation) parts. Softwares have been developed to carry out measurements of
reversible magnetization at very small excitation (H ~