Intrinsic and domain magnetism of nanocrystalline Fe, Fe(Si) and Ni(Fe) alloys produced by ball-milling

Beke, DL [Beke, Dezső (Szilárdtestfizika...), author] Institute of Physics (UD); Szabó, S [Szabó, Sándor (Nukleáris technik...), author] Institute of Physics (UD); Daróczi, L [Daróczi, Lajos (Szilárdtestfizika), author] Institute of Physics (UD); Kis, Varga M [Kis-Varga, Miklós (Anyagtudomány), author] Institute for Nuclear Research; Posgay, Gy; Harasztosi, L [Harasztosi, Lajos (villamosmérnök), author] Institute of Physics (UD)

English Scientific Abstract (Journal Article)
    Experimental results in ball-milled nanocrystalline Fe, Fe(Si) and Ni(Fe) alloys, based on our measurements of the temperature dependence of magnetization, Barkhausen-noise, hysteresis loops and Mössbauer-effect are reviewed and compared with results of measurements obtained on nanocrystalline samples produced by other techniques. It has been shown that the intrinsic magnetic properties (the saturation magnetization (Ms), the hyperfine magnetic field in the Mössbauer spectra, and the Curie-temperature (Tc)) are almost independent of the grain size (d) down to about 6 nm. This is in accordance with the newest experimental results obtained on nanocrystalline Fe produced by inert gas evaporation [1] and on Ni produced by severe plastic deformation consolidation of ball-milled powders [2] and by electrodeposition [3]. The grain size dependence of coercivity (Hc) has been found to be similar to what can be expected from the classical and random anisotropy model. The differences observed between the Hc vs grain size curves can be explained by different sample preparation techniques and to different materials. A definite correlation between the magnetic Barkhausen-noise (MBN) and the grain shape has been found in Fe which can be attributed to the formation of lamellar and textured grain structure. In Ni -- where no texture formation was observed -- there was a maximum on the MBN curve versus grain size at the same d where the sharp drop in Hc at small d values was obtained. Furthermore it was also shown -- by the separation of the effect of grain size and the residual strain (by relaxing it in an appropriate heat treatment) -- that in nanocrystalline Ni the coercivity is practically independent of the residual strain.
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    2021-10-21 22:50