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[en] Annealing of the (1.1 nm Co₉₀Fe₁₀/2.2 nm Cu)x20 and (1.1 nm Co₉₀Fe₁₀/2.2 nm Cu₈₅Ag₁₀Au₅)x20 multilayers at 235 deg. C improved their magnetoresistance as compared to the virgin samples. Annealing at higher temperatures resulted in degradation of the magnetoresistance effect. This observation raised the motivation of a detailed structural study using small-angle X-ray scattering, wide-angle X-ray diffraction, electron diffraction and transmission electron microscopy with the aim to link the structural changes in the system to the changes in the magnetoresistance. The structure studies have shown that the maximum of the magnetoresistance observed after annealing at 235 deg. C is related to the separation of Co₉₀Fe₁₀ and Cu, which are partly intermixed at interfaces after the deposition process. The decay of the GMR effect at higher annealing temperatures is caused by an increase of the interface roughness, which led in the Co₉₀Fe₁₀/Cu multilayers to occurrence of non-continuous interfaces and to short-circuiting of magnetic layers. In the Cu₈₅Ag₁₀Au₅ multilayers, the combination of small-angle X-ray scattering and wide-angle X-ray diffraction has shown that Cu₈₅Ag₁₀Au₅ did not form an alloy with the nominal composition: Only a part of Au and Ag was dissolved in the copper structure; the remainder of Ag and Au formed precipitates

[en] We report on our work on magnetic properties and their correlation with local structure in Fe-Sc nanoglasses. Samples were synthesized with a nominal composition of Fe₉₀Sc₁₀ in an inert-gas condensation (IGC) process. X-ray diffraction, Moessbauer spectroscopy as well as magnetometric characterization methods were applied to characterize the samples. Magnetometric measurements revealed a significant change of magnetic properties in the Fe rich compound marked by an increase of the Curie point to temperatures well above 300 K, which is much higher than the transition temperature in regular metallic glasses of similar composition. The maximum magnetic hyperfine field obtained from low temperature Moessbauer spectroscopy was about 37.5 T, which is much more than observed in bcc-Fe. This newly identified ferromagnetic phase is attributed to the modified short-range-order in the interfaces of adjacent amorphous nanoparticles.

[en] In this study the structural and magnetization properties of a CoFe_2O_4-based ferrofluid was investigated using x-ray diffraction (XRD), transmission electron microscopy (TEM), energy dispersive x-ray spectroscopy (EDS), Mössbauer spectroscopy, and magnetic Compton scattering (MCS) measurements. The XRD diagram indicates that the nanoparticles in the ferrofluid are inverse spinel and TEM graph shows that the ferrofluid consists of spherical nanoparticles with an average diameter of 18± 1 nm, in good agreement with the size, 19.4 nm, extracted from line broadening of the XRD peaks. According to EDS measurements the composition of the nanoparticles is CoFe_2O_4. Mössbauer spectroscopy shows that the cation distributions are (Co_0_._3_8Fe_0_._6_2)[Co_0_._6_2Fe_1_._3_8]O_4. The MCS measurement, performed at 10 K, indicates that the magnetization of the nanoparticles is similar to magnetization of maghemite and magnetite. While the magnetization of the inverse spinels are in [111] direction, interestingly, the magnetization deduced from MCS is in [100] direction. The CoFe_2O_4-based ferrofluid is found to be stable at ambient conditions, which is important for applications.