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- Ahniyaz, Anwar, et al.
(author)
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Preparation of iron oxide nanocrystals by surfactant-free or oleic acid-assisted thermal decomposition of a Fe(III) alkoxide
- 2008
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In: Journal of Magnetism and Magnetic Materials. - : Elsevier BV. - 0304-8853 .- 1873-4766. ; 320:6, s. 781-787
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Journal article (peer-reviewed)abstract
- A new non-hydrolytic, alkoxide-based route was developed to synthesize iron oxide nanocrystals. Surfactant-free thermal decomposition of the iron 2-methoxy-ethoxide precursors results in the formation of uniform iron oxide nanocrystals with an average size of 5.6 nm. Transmission electron microscope study shows that the nanocrystals are protected against aggregation by a repulsive surface layer, probably originating from the alkoxy-alkoxide ligands. Addition of oleic acid resulted in monodisperse nanocrystals with an average size of 4 nm. Mössbauer analysis confirmed that the nanocrystals mainly consisted of maghemite. Analysis of the magnetic hysteresis loop measurements and the zero field and field cooled measurements displayed an excellent fit to established theories for single-domain superparamagnetic nanocrystals and the size of the magnetic domains correlated well to the crystallite size obtained from transmission electron microscope.
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- Andreeva, M. A., et al.
(author)
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Nuclear resonant reflectivity with standing waves for the investigation of a thin 57Fe layer buried inside a superconducting Si/[Mo/Si]45/57Fe/Nb multilayer
- 2008
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In: Nuclear Instruments and Methods in Physics Research Section B. - : Elsevier BV. - 0168-583X .- 1872-9584. ; 266:1, s. 187-196
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Journal article (peer-reviewed)abstract
- A special multilayer sample Si/[Mo/Si]45/57Fe/Nb has been prepared for the depth selective investigations of the hyperfine fields in thin iron layer at low temperatures above and below the superconducting transition in the top Nb layer (Tc 8 K) by means of the nuclear resonant reflectivity with standing waves. The periodic multilayer [Mo/Si]45 below the iron layer in our sample was used as “a standing wave generator”. A weak magnetic hyperfine splitting in the 57Fe layer was detected just at low temperature. A slight variation of the nuclear resonant reflectivity time spectra measured above and below Tc was observed. At first it was supposed that this change of the spectrum shape is caused by the spatial modulation of ferromagnetic domains in the 57Fe layer caused by a proximity effect. A closer analysis, however, reveals that the spectrum variations are due to just the changes of the relative weights of the magnetic and paramagnetic phases in 57Fe layer.
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- Shahri, F., et al.
(author)
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Effects of heat treatment on the structure and magnetic properties of Al-Ge added Fe73.5-xSi13.5B9Nb3Cu alloys
- 2007
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In: Physical Review B. Condensed Matter and Materials Physics. - 1098-0121 .- 1550-235X. ; 76:2, s. 024434-
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Journal article (peer-reviewed)abstract
- In this work, we have studied the effects of the coaddition of Al(1.5 at. %)/Ge(1 at. %) and heat-treatment temperature on the structure and magnetic properties of rapidly quenched pure Fe73.5-xSi13.5B9Nb3Cu (FINEMET) alloys prepared by the single roller melt spinning process. Two series of as-spun and heat-treated alloys, 400, 480, 560, 640, and 730 degrees C for 1 h in vacuum (10(-6) Torr), were studied using various techniques such as x-ray diffraction (XRD), transmission electron microscopy (TEM), differential scanning calorimetry (DSC), Mossbauer spectroscopy, and B-H loop tracer. Mossbauer analysis carried out on both series of alloys heat treated at 560 degrees C revealed the presence of two phases, Fe3Si phase with D0(3) structure and a residual amorphous phase with reduced hyperfine field (16.9 T) compared to those of Al/Ge added (22.5 T) and pure FINEMET (similar to 23.4 T) alloys, in close agreement with XRD and TEM results. The highest maximum permeability, saturation magnetization, and the lowest coercivity were obtained for both series of alloys when heat treated at 560 degrees C. However, the magnitude of coercivity was lower for the Al/Ge substituted alloy (heat treated at 560 degrees C) compared to that of the pure FINEMET alloy. This is due to the substitution of Al atoms for Fe as confirmed by our XRD and Mossbauer results. Further, a higher ferromagnetic amorphous phase Curie temperature (T-C,T-am) was detected for the Al/Ge added alloy (322 degrees C) compared to that of the pure FINEMET alloy (317 degrees C), which is believed to be mainly related to the presence of Ge atoms in the amorphous matrix. Furthermore, the removal of stress and the setup of nanocrystallization for both series of alloys gave rise to a higher collinear magnetic moment angle. However, this was not the case for the samples heat treated at temperatures above 560 degrees C, for which the formation of the Fe-B hard magnetic phase was confirmed by our XRD, TEM, and Mossbauer results. Finally, the structural-magnetic properties relationship is discussed for various samples studied in this work.
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