Magnetic properties of nanocrystalline Fe,Ni(Fe) and Fe(Si) alloys

Results on magnetic properties of nanocrystalline pure Fe, Ni, and Fe(Si) alloys obtained in our Laboratory [1,2,3] are summarized. The grain size of powders, prod ced by ball-milling, was determined from X-ray line broadening and was 6-12 nm after about 350 hours of milling. The magnetic properties were studied by Barkhausen noise measurements technique and conventional magnetometry. The coercivity, H-C, determined from the Barkhausen-noise curves for both Fe and Ni-15%Fe showed an increasing tendency with decreasing grain size, d. This is accordance with the domain wall pinning at grain boundaries for which a 1/d law is expected. In case of Ni-15%Fe alloy a sharp decrease of H-C was observed at grain size below 20 nm which is the first experimental verification of the random anisotropy model for nanocrystalline solid solutions. Well detectable changes in the Mossbauer spectra were observed due to the grain boundaries at small grain sizes, and from the hyperfine magnetic field it was concluded that the average magnetization of nanocrystalline Fe is about 98% of the bulk value. This is in good agreement with our results obtained from the direct saturation magnetization measurements for both Fe and Ni(Fe) alloy.