A. Fnidiki

Tb/Fe amorphous multilayers: transformations under ions irradiation

Abstract Amorphous Tb/Fe multilayers were irradiated with Kr, Xe, Pb and U ions at various fluences and investigated by 57 Fe Mossbauer spectrometry at 300 K. Two processes are generally evidenced. The demixtion of Fe and Tb atoms at the interfaces produces an increase of the pure Fe thickness in the center of iron layer. The mixing of layers destroys progressively the layered structure and at high ions fluence the samples exhibit magnetic properties of amorphous alloys. The electronic stopping power threshold of mixing is estimated.

Influence of magnetic interactions on magnetic and magnetoresistive properties of Cu80Fe10Ni10 ribbons

Magnetic and magnetotransport properties measurements of Cu80Fe10Ni10 (at. %) melt spun and annealed ribbons were combined to study the magnetic interactions present in this system. Those ribbons are composed of magnetic FeNi rich precipitates embedded in a nonmagnetic Cu rich matrix. When the precipitates are small enough, they have a superparamagnetic behavior. Upon annealing the precipitates get larger and progressively turn ferromagnetic. The relatively high magnetoresistive properties are attributed to the presence of those superparamagnetic precipitates. Using Mossbauer spectrometry, Zero Field Cooled/Field Cooled and magnetization curves, the presence of interactions among the precipitates was evidenced, which degrades the magnetoresistance properties. Using Allia model, the magnetic coherence length Rm between the precipitates was calculated and compared with the mean free path of the electrons λ, with the precipitates size and the mean distance between them. Three different regimes were observed....

Effect of annealing on the magnetic and structural properties of amorphous Fe/Tb multilayers

Abstract Amorphous sputtered Fe/Tb Multilayers were annealed at different temperatures in a high-vacuum furnace and investigated at 300 K by conversion electron Mossbauer spectrometry and by high-angle X-ray diffraction, in order to study the effects of annealing on the structural and magnetic properties. At low annealing temperatures, a demixing process can be observed, which sharpens the interfaces and increases the perpendicular anisotropy. At intermediate temperatures, the mixing of the layers progressively destroys the layered structure and the sample exhibits the magnetic properties of the corresponding amorphous alloy. At higher annealing temperatures, the crystallization of α-Fe is observed.

The influence of microstructure on magnetoresistive properties of Cu80Fe5Ni15 ribbons

The influence of microstructure on magnetoresistive properties of Cu80Fe5Ni15 (at. %) melt-spun and annealed ribbons was studied. The microstructure was characterized by means of energy filtered transmission electron microscopy, small angle neutron scattering and atom probe tomography. Giant magnetoresistance (GMR) measurements were made at low temperature. The samples were annealed for 2 h at different temperatures from 400 °C to 600 °C in order to modify their microstructure and thus their GMR properties. The magnetic behavior was correlated to the structural data to explain the GMR properties that are observed. A precise structural characterization, using atom probe tomography, small angle neutron scattering and energy filtered transmission electron microscopy, is presented. It reveals that no precipitates or clusters are present into the core grains of the as spun state; thus the sample is a solid solution. The magnetic properties measurements indicate that the ribbon exhibits a superparamagnetic beha...

Xe ions irradiation on bcc-Fe/Tb multilayers

Abstract Two bcc-Fe/Tb MLs with t Fe far from and close to the limit of crystallization of Fe layers were irradiated with Xe ions at various fluences and investigated by 57 Fe Mossbauer spectrometry at 300 K. Two structural effects were evidenced: the usual mixing of layers and a demixing of the Fe and Tb atoms at the interfaces. The first process, observed in the two samples, destroys progressively the layered structure and leads to the formation of the corresponding amorphous alloy at high fluence. The second process, observed only at low fluence before the step of mixing for the multilayer close to the limit of crystallization of Fe layers, features the thermal metastability of this multilayer which relaxes towards a minimal energy state. It increases the pure iron part in the center of the iron layers, thus sharpening the interfaces.

Fe-implanted 6H-SiC: Direct evidence of Fe3Si nanoparticles observed by atom probe tomography and 57Fe Mössbauer spectroscopy

In order to understand ferromagnetic ordering in SiC-based diluted magnetic semiconductors, Fe-implanted 6H-SiC subsequently annealed was studied by Atom Probe Tomography, 57Fe Mossbauer spectroscopy and SQUID magnetometry. Thanks to its 3D imaging capabilities at the atomic scale, Atom Probe Tomography appears as the most suitable technique to investigate the Fe distribution in the 6H-SiC host semiconductor and to evidence secondary phases. This study definitely evidences the formation of Fe3Si nano-sized clusters after annealing. These clusters are unambiguously responsible for the main part of the magnetic properties observed in the annealed samples.

Fe implantation effect in the 6H-SiC semiconductor investigated by Mössbauer spectrometry

P-doped 6H-SiC substrates were implanted with 57Fe ions at 380 °C or 550 °C to produce a diluted magnetic semiconductor with an Fe homogeneous concentration of about 100 nm thickness. The magnetic properties were studied with 57Fe Conversion Electron Mossbauer Spectrometry at room temperature (RT). Results obtained by this technique on annealed samples prove that ferromagnetism in 57Fe-implanted SiC for Fe concentrations close to 2% and 4% is mostly due to Fe atoms diluted in the matrix. In contrast, for Fe concentrations close to 6%, it also comes from Fe in magnetic phase nano-clusters. This study allows quantifying the Fe amount in the interstitial and substitutional sites and the nanoparticles and shows that the majority of the diluted Fe atoms are substituted on Si sites inducing ferromagnetism up to RT.P-doped 6H-SiC substrates were implanted with 57Fe ions at 380 °C or 550 °C to produce a diluted magnetic semiconductor with an Fe homogeneous concentration of about 100 nm thickness. The magnetic properties were studied with 57Fe Conversion Electron Mossbauer Spectrometry at room temperature (RT). Results obtained by this technique on annealed samples prove that ferromagnetism in 57Fe-implanted SiC for Fe concentrations close to 2% and 4% is mostly due to Fe atoms diluted in the matrix. In contrast, for Fe concentrations close to 6%, it also comes from Fe in magnetic phase nano-clusters. This study allows quantifying the Fe amount in the interstitial and substitutional sites and the nanoparticles and shows that the majority of the diluted Fe atoms are substituted on Si sites inducing ferromagnetism up to RT.