D. Lemarchand

Structural investigation of the metastable compound A1 in an as-cast FeNd eutectic alloy

Abstract In this paper some structural and chemical informations about the compound A1 are given. Transmission electron microscopy investigations reveal that it is composed of a mixture of two nanocrystalline compounds A1α and A1β, with atomic compositions close to Nd 20 Fe 80 and Nd 40 Fe 60 , respectively. Their formation is described in a metastable phase diagram including also NdFe 2 , and is confirmed by thermodynamic calculations on the basis of Miedemas model.

Investigation of the δ and μ phases in the NdFeAl system

Abstract Nd Fe Al alloys containing either δ or μ phase (Al content in the 2.5–11 at.% range) were studied by X-ray diffraction analysis and Mossbauer spectrometry. A lattice expansion of the δ phase (composition Nd 6 Fe 14− x Al x ) is observed, due to the substitution of Al for Fe in the 16 l 2 site of space group I 4/mcm. The room-temperature Mossbauer spectrum is paramagnetic for x = 2.8 and magnetic for x = 2. For x = 2, the mean iron moment is estimated to be 2.0 ± 0.1 μ B . Room-temperature Mossbauer spectra of the μ phase (Nd 33.3 Fe 66.7− x Al x with x = 5.3 and 3.7) are magnetic, and the results support a slight distribution of environments around the Fe atoms due to the substitution of Al for Fe.

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....

Transmission electron microscopy study of the μ phase in the Fe-Nd-Al system

Abstract Transmission electron microscopy was performed on the μ phase in the Fe-Nd-Al system. The structure of μ consists of a long period stacking of planes, typical of polytypism. These basal planes exhibit a diffraction pattern with a six-fold symmetry, characteristic of a two-dimensional hexagonal structure ( a =1.65 nm). A 12R type stacking sequence was recognized, with c = 15 nm.

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...

Microstructural and thermomagnetic investigation of rapidly solidified Nd-Fe(-Al) eutectic alloys

Abstract An eutectic Fe-Nd(-Al) alloy was investigated, where a 3-phase equilibrium Nd 5 Fe 17 + μ + Nd was found. Their stability is discussed for different heat-treatments. The evolution of the microstructures with a continuously variable cooling rate is studied.