Marek Kuzminski

Nanocrystalline metallic glass-an unusual particulate medium

The expectation that nanocrystalline Fe-based metallic glass may show a variety of magnetic phases is confirmed experimentally. It is shown that, depending on the annealing conditions (resulting in controlled crystallite size as well as the volumetric fraction of the crystalline phase), the particles exhibit superparamagnetic or superferromagnetic behavior at temperatures above the Curie point of the amorphous matrix. At sufficiently low temperatures (around room temperature), the samples behave ferromagnetically as expected for typical nanocrystalline metallic glass. >

Magnetoresistance in nanocrystalline Fe-based metallic glass

The ferromagnetic anisotropy of resistivity as well as the effective resistivity of nanocrystalline Fe-based metallic glasses with different volumetric fraction of crystalline phase have been studied. It has been shown that the ferromagnetic anisotropy of resistivity can be considered as a sum of two independent contributions of the opposite sign-positive, originating from the residual amorphous matrix and negative from the crystallites. >

Indication of Intrinsic Macroscopic Forces Affecting Magnetic Properties of Fe-Nb/Mo-Cu-B-Si Ribbons

Si-rich (at.% Si >; 12) Fe-Nb/Mo-Cu-B-Si nanocrystalline ribbons are already successfully used in industry. Still the impact of intrinsic macroscopic stresses on magnetic anisotropy is not known in enough detail. Domain structure, hysteresis loops and surface chemistry have been studied in the as-annealed (nanocrystalline) state as well as the response to surface removal by etching. Creep-induced anisotropy established during annealing was found to be the essential source of the observed anisotropy. Apparently smooth gradient of transversal to longitudinal creep-induced anisotropy was identified from air-side center across the ribbon width as well as across the ribbon thickness. The relative rise of transversal anisotropy due to surface removal points to different surface etching efficiency. Raman spectroscopy confirmed the presence of ferrous oxides on both the ribbon surfaces. The existence of a defined oxide layer generating the macroscopic stress was not indicated.

The influence of superparamagnetic particle size distribution and ferromagnetic phase on GMR in melt spun Cu-Co granular alloys

Magnetic characteristics and structure of granular Cu/sub 90/Co/sub 10/ alloy were investigated in order to explain their relationship with electric transport properties. The annealed sample contains mainly Co-particles with sizes of a few nanometers and some much larger particles or agglomerations, which are not superparamagnetic. It is shown that the ferromagnetic phase contribution to the total magnetization (calculated applying the new, invented method) and differentiated surface to volume ratio of superparamagnetic particles are the main sources of the observed deviation of the magnetoresistance characteristics from that expected theoretically for superparamagnetic particles of equal size.