Browsing by Author "Martínez-Blanco, D."

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    Hydrothermal synthesis of co nanoparticles : structure, morphology and magnetic properties
    (World Scientific, 2021) Bouelkreb, I.; Guittoum, A.; Hemmous, M.; Martínez-Blanco, D.; Gorria, P.; Blanco, J. A.; Boukherroub, N.
    We have investigated the crystal structure, the microstructural and morphological characteristics, as well as the magnetic properties of Co nanoparticles (NPs) synthesized by a hydrothermal method. A series of samples has been elaborated for different concentrations of sodium hydroxide. The analysis of X-ray diffraction patterns, using two different wavelengths, has evidenced the coexistence of both α-Co and β-Co phases in the samples. The lattice parameter for both phases is in good agreement with those values expected for their bulk Co counterparts; the grain sizes of NPs were found to be dependent on the NaOH concentration. The scanning electron microscope micrographs show that Co NPs are agglomerated forming micrometer-sized entities whose shape evolves, indicating that the synthesis process affects the morphology of the powdered samples. Magnetic measurements indicate that the coercivity is slightly larger, HC>200 Oe, for Co NPs with dendritic-like shape, probably due to an increase in the magnetocrystalline anisotropy
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    Microstructure and magnetic properties of nanostructured (Fe0.8Al0.2)100-xSix alloy produced by mechanical alloying
    (Elsevier, 2015) Boukherroub, Nadia; Guittoum, A.; Laggoun, A.; Hemmous, M.; Martínez-Blanco, D.; Blanco, J.A.; Souami, N.; Gorria, P.; Bourzami, A.; Lenoble, O.
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    The role of silicon on the microstructure and magnetic behaviour of nanostructured (Fe0.7Co0.3)100_xSix powders
    (Elsevier, 2017) Hocine, M.; Guittoum, A.; Hemmous, M.; Martínez-Blanco, D.; Gorria, P.; Rahal, B.; Blanco, J.A.; Sunol, J.J.; Laggoun, A.
    Single-phase(Fe0.7Co0.3)100 xSix nanostructured powders(x¼0,5, 10,15and20)havebeenelaboratedby mechanical alloyinginordertoinvestigatetheeffectofsilicononthemicrostructureandmagnetic properties ofthesealloys.AdisorderedFe(Co,Si)solidsolutionwithbodycentredcubic(bcc)crystal structure isformedafter72hofmillingforallthecompositions.TheadditionofSigivesrisetoapro- gressivedecreaseofthelatticeparameter,fromabout2.865ÅforthebinaryFe70Co30 compound downto 2.841Åforthepowderwith x¼20. ThesamplewiththeuppermostSicontentexhibitsthelowestvalue for themeangrainsize(E10nm)aswellasthelargestmicrostrain(above1.1%).Allthesamplesare ferromagnetic atroomtemperature,althoughthesaturationmagnetizationvaluereducesalmostlinearly by addingSitothecomposition.Asimilartrendisobservedforthehyperfine magnetic field obtained from theanalysisoftheroomtemperatureMössbauerspectra.Thehyperfine field distributionsshowa broad double-peakshapefor x40, whichcanbeascribedtomultiplelocalenvironmentsfortheFe atoms insideadisorderedsolidsolution
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    The role of siliconon the micro structure and magnetic behaviour of nanostructured (Fe0.7Co0.3)100_xSix powders
    (Elsevier, 2017) Hocine, M.; Guittoum, A.; Hemmous, M.; Martínez-Blanco, D.; Gorria, P.; Rahal, B.; Blanco, J.A.; Sunol, J.J.; Laggoun, A.
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    Structure, Microsctructure and Magnetic Properties of Ternary (Fe0.6Al0.4)100-xSix Nanostructured Powders: Effect of Si Addition
    (2019) Boukherroub, N.; Hemmous, M.; Guittoum, A.; Martínez-Blanco, D.; Souami, N.; Gorria, P.; Blanco, J.A.
    Nanostructured (Fe0.6Al0.4)100-xSix powders with x= 0, 5, 10, 15 and 20 at.% were elaborated by means of mechanical alloying for a fixed milling time of 72 h. We have investigated the effect of silicon addition on the microstructure and magnetic properties of these ternary alloys. X-ray diffraction experiments reveal that these powders are single-phase disordered solid solutions with body centered cubic crystal structure. The lattice parameter diminishesalmost linearly as the Si content increases. The mean crystallite size,, is around three times smaller for the samples with higher amount of Si (≈ 10 nm) compared with that of the binary alloy (27 nm). Moreover, the volume fraction of grain boundaries (fgb) seems to be higher with increasing the Si content, as well as both dislocation density (ρ) and lattice microstrain (<ε>),that follow alinear trend. The SEM images show that the Si helps in refining the shape and size of the powder particles, leading to a nearly homogeneous small particles.The addition of Si strongly affects the value of the saturation magnetization, Ms, that falls nearly an order of magnitude for the sample with 20 at.% Si, while the coercivity remains almost unchanged. The Mössbauer spectra show the presence of a sextet (ferromagnetic phase) and a singlet or a doublet (non ferromagnetic phase), except for the sample corresponding to x = 10, where only one singlet is observed in the spectrum.