Inhomogeneous Properties of Ionic Semi-Spin-Glasses Studied by Mössbauer Spectroscopy

Fe 1−x Si x (0.15 < x < 0.375) alloys have been prepared by a rapidquenching technique. X-ray diffraction patterns show that these alloys consist of submicron grains between 100 and 300 nm. The DO 3 cubic symmetry could be obtained for Si content up to 34 at.% Si. This feature is particularly interesting since alloys containing more than 26 at.% Si and cast with usual techniques consist of a mixture of Fe 3 Si and Fe 5 Si 3 . The magnetization, Curie temperature and resistivity data for these fine-grained alloys are consistent with those for bulk alloys for Si content below 25 at.% Si. In contrast, the structural and physical data for single-phase alloys with 28-34 silicon content are reported for the first time. Within this composition range, the magnetization and Curie point values roughly correspond to those suggested by the extrapolation of existing data. However, the resistivity shows an unexpected marked increase above 25 at.% Si. The values of resistivity, magnetization and effective anisotropy of soft-magnetic nanocrystalline Fe 2 Si are found to be 200 µ cm, 0.6 T and 15 kJ m −3 respectively, suggesting that this alloy has potential for highfrequency applications.

Section: Methodsmentioning

confidence: 99%

Structural and magnetic properties of metastable Fe_1-xSi_x(0.15<x<0.34) alloys prepared by a rapid-quenching technique

Varga

Mazaleyrat

Kováč

et al. 2002

“…The analysis of Mössbauer spectra was performed using the Mosfit program [17]. The values of isomer shift were quoted relative to that of bcc-Fe at 300 K. In the case of amorphous alloys, the description only consists in a discrete distribution of hyperfine field or of quadrupolar splitting linearly correlated with that of isomer shift, below and above the Curie point of the asquenched amorphous alloy, respectively.…”

Section: Methodsmentioning

confidence: 99%

Influence of microstructure on the magnetic and mechanical behaviour of amorphous and nanocrystalline FeNbB alloy

Škorvánek

Švec

Grenèche

et al. 2002

The formation of a nanocrystalline structure and its influence on the magnetic and mechanical properties in a ternary Fe 80.5 Nb 7 B 12.5 alloy has been investigated using a variety of complementary methods. The crystallization studies performed by DSC calorimetry, magnetization and electrical resistivity measurements have confirmed a two-stage nature of the primary crystallization process. The microstructure in the series of heat-treated amorphous and nanocrystalline specimens with different volume fractions of crystalline phase was examined by transmission electron microscopy, x-ray diffraction and 57 Fe Mössbauer spectrometry. The results obtained by a combination of static magnetic measurements and Mössbauer spectrometry have indicated a higher degree of structural and magnetic inhomogeneity of the residual amorphous phase after nanocrystallization. Striking differences in the magnetic hardening regime at elevated temperatures have been observed for the samples with different volume fractions of nanocrystalline particles. The strongest magnetic hardening effects are visible for the samples exhibiting a medium degree of crystallinity, while the best soft-magnetic properties are obtained for the samples where the primary crystallization process is nearly finished. The ductility tests have revealed that the transition from ductile to brittle behaviour develops predominantly in an amorphous phase just before crystallization and the subsequent crystallization causes only slight changes in the embrittlement level. On the other hand, the hardness is rather insensitive to the structural relaxation processes before crystallization and its value increases proportionally to the volume fraction of precipitated nanocrystalline grains.

“…Transmission Mössbauer spectra were measured using a conventional constant acceleration spectrometer as a function of temperature, between 4 K and room temperature (RT). Experimental Mössbauer spectra were fitted with Brand's NORMOS program [10] and with the MOSFIT program developed by Teillet and Varret [11] using two components below the amorphous Curie temperature (T C ): one crystalline magnetic sextet for crystalline α-Fe, when present, and a distribution of hyperfine fields (P (B hf )) to describe the sextet with broadened and overlapped lines assigned to the amorphous phase. Above T C , the quadrupolar doublets with broad lines are reproduced with distributions of quadrupole splitting, P ( ).…”

Section: Methodsmentioning

confidence: 99%

Magnetic and Mössbauer study of multiphase Fe-Zr amorphous powders obtained by high energy ball milling

Pizarro¹,

Garitaonandia²,

Plazaola³

et al. 2000

The amorphous system Fe-Zr has been extensively studied due to its particular magnetic behaviour, especially in the concentration range around 90 at.% Fe, only accessible by rapid quenching. We have extended the study to lower Fe content alloys, by using mechanical alloying to synthesize Fex Zr100 - x amorphous powders with x = 65, 70, 75. Mössbauer spectra and magnetization measurements have been performed as a function of temperature. Different magnetic measurements were performed to characterize the Curie temperatures of these multiphase samples and hyperfine field (Bhf ) distributions, P (Bhf ), were used to fit Mössbauer spectra below the Curie temperature (TC ) and quadrupole splitting distributions, P ( ), above TC , in agreement with the amorphous structures. The hyperfine field distributions of as-milled samples are characterized by two maxima and are fitted with two Gaussian curves that evolve with temperature in position, intensity and width. This bimodal behaviour has been also found in higher Fe content FeZr alloys as well as in ternary alloys with boron, and with nickel, and can be interpreted as arising from different neighbourhood Fe sites. The rather uncommon P ( ) are also interpreted in the same terms.