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Mössbauer study of the Heusler-type Fe2MAl compounds for M = V, Cr, Fe, Co, Ni

Popiel E., Zarek W., Tuszyński M.

Nukleonika

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2004

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Vol. 49,suppl.3

49-52

EN

The crystal structure and magnetic properties of Fe2MAl compounds for M = V, Cr, Fe, Co and Ni were investigated by X-ray, magnetostatic and Mössbauer effect methods. It was found that the investigated compounds possess not perfectly ordered fcc structure of the L21-type. With increasing number of 3d electrons of M component the transition from the paramagnetic to ferromagnetic behaviour follows. Mössbauer spectra were analysed by a hyperfine field distribution method. They are characterictic of the ferromagnetic phase for M = Fe, Co and Ni and indicated the early observed preference of these atoms for the Fe sites.

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Mössbauer study of the El Hammami olivine-bronzite meteorite

Zarek W., Popiel E., Tuszyński M., Teper E.

Nukleonika

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2004

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Vol. 49,suppl.3

59-62

EN

The phase composition of the El Hammami meteorite was investigated by X-ray, magnetostatic, Mössbauer effect and environmental scanning electron microscopy methods. Performed investigations indicated that this meteorite consists of aluminosilicates, olivine (Mg,Fe)2SiO4, pyroxene (Ca,Mg,Fe)SiO3, kamacite (bcc Fe-Ni alloy) and troilite (FeS). Some inclusions of Ti and Cr were observed by scanning electron microscopy. The concentration of Ni in kamacite was determined by comparison of the Mössabauer spectra of Fe-Ni phase in the meteorite with those for synthetic bcc Fe-Ni alloys (5, 10, 25% Ni).

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57Fe Mössbauer study of stilpnomelane and associated chlorite from Polish granite pegmatites

Malczewski D., Popiel E., Sitarek A.

Nukleonika

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2004

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Vol. 49,suppl.3

43-48

EN

This paper reports the results of 57Fe Mössbauer study of stilpnomelane K0.6Fe6(Si8Al)(O,OH)27 .2H2O from Żółkiewka (Lower Silesia, Poland). Stilpnomelane in paragenesis with chlorite, tourmaline, claevelandite and zeolites has been found in granite pegmatites in quarries at Żółkiewka. The samples of naturally weathered stilpnomelane and chlorite from the same fragment of rock were also studied. The Mössbauer spectrum of an untreated sample could be fitted to two Fe2+ doublets and two Fe3+ doublets. The Fe2+ doublets have similar isomer shifts, but they distinctly differ in values of quadrupole splittings. Ferric iron, octahedrally coordinated occurs in three different environments represented by two doublets. The first of them, assigned to combined M1 + M2 positions and the second one assigned to M3 site with parameters IS = 0.36 mm/s and QS = 2.07 mm/s is visible in the spectra up to 880°C. This doublet is characteristic of stilpnomelane and can be regarded as a "fingerprint" of this mineral. After heating at 200°C, the relative content of Fe2+, ÓFe2+/ÓFe, decreases to 0.22 what means a 50% decrease in comparison to the initial value observed in the untreated sample. At about 1000°C, complete breakdown of the stilpnomelane structure takes place and the Mössbauer spectrum consists of two sextets and two ferric doublets. Abnormally high content of Fe2+ in naturally weathered stilpnomelane (0.70) comparing to the untreated sample of stilpnomelane (0.45) indicates that the sample had to be subjected to hydrothermal processes operating locally. Almost the same contents of divalent iron and hyperfine parameters of Fe2+ and Fe3+ doublets in weathered stilpnomelane and associated chlorite suggest that the process of chlorite transformation into stilpnomelane seems to be very probable.

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Crystal order and magnetic properties of Fe2.4V0.6Al alloy studied by magnetostatic and Mössbauer methods

Popiel E., Zarek W., Kapuśniak Z., Tuszyński M.

Nukleonika

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2003

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Vol. 48,suppl.1

65-70

EN

Performed investigations showed that the magnetic properties of the Fe2.4V0.6Al alloy markedly depend on the degree of atomic order of its cubic structure. The atomically disordered alloy with A2 (bcc) type structure exhibits ferromagnetic properties. Its Mössbauer spectra can be described by the hyperfine field distribution connected with various local environments of Fe atoms. Alloys with B2 (sc) and DO3 (fcc) type structure do not exhibit magnetic transition above 4.2 K. High values of the magnetization and its strongly non-linear variation with magnetic field intensity in a wide temperature range suggest the presence of magnetic iron clusters in these alloys. Superparamagnetic relaxation times of the order of 10-9 s and 5 × 10-8 s correspond to the largest magnetic clusters with a magnetic moment of 4 × 103 žB in B2 and 104 žB in DO3-type structure, respectively. Mössbauer spectra of these alloys confirm lack of the magnetic order and also suggest the presence of the Fe magnetic clusters with those relaxation times. It was shown that the increase of atomic order of the crystal structure causes formation of the Fe magnetic clusters and disappearing of the magnetic order.