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Crystallization of amorphous Fe-Cr-B alloys investigated with high heating rates

Kamasa P, Varga L K, Myśliński P, Rassolov S G, Maksimov V, Idzikowski B

Materials Science Poland

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2008

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Vol. 26, No. 4

947--952

EN

Rapid annealing of metallic glasses results in their physical properties different from those stemming from isothermal or non-isothermal annealing with slow heating rates. Differential thermal analysis (DTA) with heating rates up to 2500 K min-1 was applied to investigate amorphous alloys of the composition Fe85-xCrxB15 (x=0, 1, 5) in order to follow the crystallization process. The results have been compared with those obtained with the usual low heating rate processes available from the commercial DSC method. Simultaneously recorded high heating rates magnetic susceptibilities complement the thermal measurements and reveal an interesting phenomenon of suppression of the decomposition of the residual amorphous phase when the heating rates exceed 1250 K min-1, 550 K min-1 and 250 K min-1 for x=0, 1 and 5, respectively. Both, the high heating rate and the Cr addition facilitate the formation of nanostructure which is stable against a further decomposition.

2

Scalling approach to describe the nanocrystallization kinetics in Al based bulk amorphous alloys.

Fazakas E., Varga L.K.

Archives of Materials Science

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2004

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Vol. 25, nr 4

365-372

EN

The scalling approach was found to apply to the nano-crystallization stage in the framework of the Johnson-Mehl-Avrami theory of nucleation and growth phenomena. By rescalling the time axis for each annealing temperature, the data fall on a universal curve of the JMA form x(tau) = 1 - exp(- tau n In 2), where tau = t/t1/2, with t1/2 = t1/2 (Tann) is related to the nucleation rate and is taken the time at which crystallization is 50% complete. The scalling time parameter, t1/2, was found to diverge with decreasing annealing temperature, defining a characteristic freezing temperature, Tf. Ts parameter can be fitted to a Williams-Landel-Ferry temperature dependence, suggesting a correlation between Tf and Tg (the glass transition temperature).

3

Micromagnetic calculations of magnetic structures in nanoparticles.

Kakay A., Varga L.K.

Archives of Materials Science

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2004

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Vol. 25, nr 4

431-439

EN

Remnant states of sphere-like particles have been investigated for different ferromagnetic metallic materials by numerical micromagnetic calculations in order to establish the critical radius for the monodomain-vortex transition. The obtained radii have been compared with those obtained earlier by order of magnitude estimates and analytical micromagnetic calculations. A hard-axis oriented vortex state has been found as a transition between the monodomain and easy-axis oriented vortex magnetization states.

4

Metal-metal and metal-insulator type soft magnetic nanocomposite.

Varga L.K., Mazaleyrat F.

Archives of Materials Science

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2004

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Vol. 25, nr 4

311-320

EN

Some new developments in the field of soft magnetic nanocomposites are reviewed concerning their high temperature and high frequency limit of applicability. Magnetic decoupling temperature gives the temperature limits, which can be best determined through the temperature dependence of the coercive field distribution. The frequency limit can be improved by dimminishing the effective permeability, and the thickness by increasing the resistvity. Examples are given for all these possibilities presenting the stress annealed Finemet, pulse deposited nano-Fe/Fe-oxide multilayers and plasma sprayed bulk amorphous thick layers.