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The influence of the structure of metastable τ - phase on magnetic hysteretic properties of Мn55.5Аl44С0.5 alloy

Alexander Korznikov 1Zbigniew Pakiela 2Galia Korznikova 1Krzysztof J. Kurzydlowski 2

1. Institute for Metals Superplsticity Problems, Russian Academy of Sciences, Ufa, Russian Federation
2. Warsaw University of Technology, Faculty of Materials Science and Engineering (InMat), Wołoska 141, Warszawa 02-507, Poland


Ferromagnetism of Mn-Al system alloys is determined by a metastable τ-phase, which is usually stabilized by small amount of C. This phase formed under specific thermal treatment, it has an ordered L10 type face centered tetragonal structure and exhibits rather high value of magnetic anisotropy constant. For a given chemical composition the as-cast state the coercivity value is usually low. The improvement of magnetic properties may be attained by plastic deformation. For studying domain structure and magnetic hysteretic hysteretic properties the samples with different structural states of τ- phase were processed by means of deformation and thermal treatment. After annealing at 900°C the cast samples were cooled in the oil. During this processing the coarse grained nonmagnetic ε-phase transformed into a needle type τ-phase. Subsequent extrusion under different temperature - strain rate conditions and additional annealing enables formation of τ-phase with submicron mean grain size (0.5-0.7 μm) and different dislocation density(109-1011сm-2). It is shown that coercivity increases from 303 to 368 kA/m as the grain size decreases in submicron grained samples, and does not depend on the dislocation density. In these samples most of the grains in the initial nonmagnetized state have multidomain structure and contain several domains with alternating antiparallel directions of magnetization divided by straight parallel Bloch type domain walls. The estimation of the criterion of single domain state suggests that magnetization occurs by means of nucleation of the reverse domains in submicron structural state and by means of domain walls displacement in nanocrystalline state. That means that in spite of significant refinement of τ-phase a single domain state has not been achieved in either of the structural states under study.


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Presentation: Poster at E-MRS Fall Meeting 2006, Symposium I, by Alexander Korznikov
See On-line Journal of E-MRS Fall Meeting 2006

Submitted: 2006-04-26 06:21
Revised:   2009-06-07 00:44