E Nunes

Single magnetic domain precipitates of Fe/Co and Fe and Co in Cu matrix produced from (Fe-Co)/Cu metastable alloys

Structural and magnetic properties of nanocrystalline Fe2Co and (Fe2Co)0.30 Cu0.70 alloys prepared by high energy ball milling have been studied basically by x-ray, Mossbauer spectroscopy and magnetization measurements. For the Fe2Co alloy case, the Mossbauer measurements indicate that the sample with 160 hours of milling has two magnetic components with the same average hyperfine parameters: one magnetic crystalline component associated with the bcc Fe2Co phase and another component attributed to the small particles of the same bcc Fe2Co phase (SP-Fe2Co). (Fe2Co)0.30Cu0.70 alloys have been prepared by milling in two different ways: (1) starting from the mixture of Fe2Co milled alloy and pure Cu powders (sample I) and (2) milling of the elemental powder mixture of Fe, Co and Cu (sample II). The x-ray diffraction and bulk magnetization results of samples I and II indicate the formation of a (Fe2Co)0.30Cu0.70 supersaturated solid solution, with features of a ferromagnetic material and Tc at about (420±1) K. High temperature magnetization measurements of the (Fe/Co)Cu milled materials show particle precipitation effects. Heat treatment at 675 and 875 K of the final milled materials leads to different results: in the sample I case to the precipitation of single magnetic Fe/Co particles into the Cu matrix, and in the case of sample II the precipitation of single magnetic particles of Fe and of Co into the Cu matrix.

Solubility study of Fe0.95Pb0.05 alloy prepared by high energy ball milling

Abstract In this work Pb 0.05 Fe 0.95 nanostructured alloy was prepared by high energy ball milling under argon atmosphere. X-ray diffraction (XRD), differential scanning calorimetry (DSC) and Mossbauer measurements were performed in the milled samples to study the alloying process and the structural variation with milling time. XRD and DSC results of Pb 0.05 Fe 0.95 alloy indicate the presence of free Pb metal for milling times shorter than 20 h. On the other hand, XRD and Mossbauer results show that the final Pb 0.05 Fe 0.95 alloy (sample milled for 310 h) is constituted by four nanocrystalline phases: b.c.c.-Fe, possibly with Pb impurities trapped in it, Fe/Pb phase and finally two Fe oxide phases (Fe 1− x O and Fe 3 O 4 ). The relative areas corresponding to these phases in the Mossbauer spectrum are 58% for the b.c.c.-Fe, 12% for the b.c.c. Fe/Pb alloy, and 30% for the Fe oxide phases. The Fe/Pb phase, with approximate composition Fe 0.71 Pb 0.29 , is being reported for the first time and it is also shown that this phase is thermally stable up to 650 K.

Amorphization of obtained by milling under different atmospheres

In the present work, high-energy milling under two different atmospheres was applied to the intermetallic compound and to the chemical elemental powders of Er and Fe with stoichiometric composition. Sample A is the compound milled under Ar, sample B the compound milled under and sample C the elemental powders milled under atmosphere. X-ray diffraction (XRD) and Mossbauer spectroscopy (MS) results of the samples A and B show a segregation process with increase of the milling time. Under atmosphere, the initial compound was nearly dissociated with 50 h of milling, while with Ar atmosphere the segregation process was completed with 100 h of milling. From the analysis of the XRD and MS results, it was possible to observe the appearance of other phases at intermediate milling times, in both samples A and B. One phase was associated with an amorphous alloy with a magnetic ordering temperature, obtained by AC magnetic susceptibility, at about 190 K, a second phase was attributed to nanocrystallites of and a third one associated with an fcc Er high-pressure phase stabilized by N atoms. In the case of sample B, for milling times longer than 400 h, XRD and MS results indicate the presence of an Fe-Er-N disordered alloy, with magnetic ordering temperature above room temperature. The XRD and MS results of sample C show the formation of an amorphous phase, with about 87% of MS relative area in this phase at 68 h of milling.

Low field magnetic studies of some alloys

Polycrystalline pure Gd and (x = 0.15, 0.25, 0.27 and 0.50) alloys have been studied by low field magnetic susceptibility , magnetization and electrical resistivity measurements. Measurements were also performed on samples with low demagnetizing factor geometry in order to study the ground state properties of these systems. For hexagonal close-packed (hcp) samples the effect of spin reorientation is indicated by a broad peak in the susceptibility curve and it shifts rapidly to lower temperatures with increasing La content in Gd metal. The spin reorientation effect is not observed in the samples with La concentration higher than 15%. The and resistivity measurements indicate a ferromagnetic transition at for 15% La concentration. For the Sm-type structure sample, with x = 0.27, two magnetic transition peaks are observed at 135 K and 113 K and helical antiferromagnetic order is suggested. Finally, the results for the x = 0.50 alloy with double hexagonal close-packed (dhcp) crystalline structure indicate a spin-glass magnetic phase type, below . Observed magnetization remanent effects, in this latter case, give additional support for the presence of the spin-glass phase.

Synthesis and characterization of nanostructured iron compounds prepared from the decomposition of iron pentacarbonyl dispersed into carbon materials with varying porosities

This work describes the production and characterization of carbon-iron nanocomposites obtained from the decomposition of iron pentacarbonyl (Fe(CO)5) mixed with different carbon materials: a high surface area activated carbon (AC), powdered graphite (G), milled graphite (MG), and carbon black (CB). The nanocomposites were prepared either under argon or in ambient atmosphere, with a fixed ratio of Fe(CO)5 (4.0 mL) to carbon precursor (2.0 g). The images of scanning electron microscopy and the analysis of textural properties indicated the presence of nanostructured Fe compounds homogeneously dispersed into the different classes of pores of the carbon matrices. The elemental Fe content was always larger for samples prepared in ambient atmosphere, reaching values in the range of 20–32 wt%. On the other hand, samples prepared under argon showed reduced Fe content, with values in the range 5–10 wt% for samples prepared from precursors with low surface area (G, MG, and CB) and a much higher value (~19 wt%) for samples prepared from the precursor of high surface area (AC). Mössbauer spectroscopy and X-ray diffractometry showed that the nanoparticles were mostly composed of iron oxides in the case of the samples prepared in oxygen-rich ambient atmosphere and also for the AC-derived nanocomposite prepared under argon, which is consistent with the large oxygen content of this precursor. For the other precursors, with reduced or no oxygen content, metallic iron and iron carbides were found to be the dominant phases in samples prepared under oxygen-free atmosphere. The samples prepared in ambient atmosphere and the AC-derived sample prepared under argon exhibited superparamagnetic behavior at room temperature, as revealed by temperature-dependent magnetization curves and Mössbauer spectroscopy.