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Publications (159)
Through a combination of multimodal operando, as well as and ex situ , and in situ techniques: Unravelling the intrinsic factors underlying the electrochemical activation of maricite-NaFePO 4 .
Cobalt ferrite (CFO) is a promising candidate for magnetostrictive applications like actuators or sensors. We have recently shown that uniaxial magnetic anisotropy can be induced in CFO by reactive sintering using spark plasma sintering (SPS), which leads to an improvement of its magnetostrictive properties. However, the origin of the anisotropy an...
Exchange bias (EB) properties have become especially important in hollow magnetic nanoparticles (MNPs) due to the versatility and reduced size of these materials. In this work, we present the synthesis and study of the EB properties of iron-oxide-based hollow MNPs and their precursors Fe/iron oxide MNPs with core/void/shell structure. The two mecha...
Among iron oxide phases, magnetite (Fe3O4) is often the preferred one for nanotechnological and biomedical applications because of its high saturation magnetization and low toxicity. Although there are several synthetic routes that attempt to reach magnetite nanoparticles (NPs), they are usually referred as “IONPs” (iron oxide NPs) due to the great...
The currently existing magnetic hyperthermia treatments usually need to employ very large doses of magnetic nanoparticles (MNPs) and/or excessively high excitation conditions (H × f > 1010 A/m s) to reach the therapeutic temperature range that triggers cancer cell death. To make this anticancer therapy truly minimally invasive, it is crucial the de...
The influence of both the Co addition and the internal stress on the atomic level magnetism is comparatively studied in Ni50Mn37Sn13 and Ni45Mn38Sn13Co4 alloys by magnetic measurements and 119Sn Mössbauer spectroscopy. The results show that the saturation magnetization and the hyperfine field follow the same temperature trend. The internal stress s...
ThMn12 nitrides are good candidates for high performance permanent magnets. However, one of the remaining challenges is to transfer the good properties of the powder into a useful bulk magnet. Thus, understanding the denitrogenation process of this phase is of key importance. In this study, we investigate the magnetic and structural stability of th...
A series of (Nd1−xSmx)Fe11Ti alloys with the ThMn12 crystal structure have been fabricated and characterized in order to promote a strong uniaxial anisotropy in NdFe11Ti without the need of nitrogenation. The compounds show small changes in the lattice parameters and cell volume, as well as Curie temperature and spontaneous magnetization. The aniso...
We present results concerning the fabrication of a new magnetorheological fluid with FeCo magnetic nanoparticles (NPs) as magnetic fillers. These NPs have been fabricated by using the chemical reduction technique and show a pure crystalline phase with size ranging among 30–50 nm and high magnetization, 212 ± 2 A m² kg⁻¹. They agglomerate due to the...
The influence of quenching rate and nitrogenation in melt-spun Nd1.2Fe10.6Mo1.4 has been investigated in terms of microstructure, phase formation and magnetic properties. Increasing the quenching rate leads to smaller grain size. However, it also implies a change in the crystallized phase structure. We obtained a pure ThMn12 (1:12) structure at que...
Local heat generation from magnetic nanoparticles (MNPs) exposed to alternating magnetic fields can revolutionize cancer treatment. However, the application of MNPs as anticancer therapy is limited by serious drawbacks. Foremost among these are the fast uptake and biodegradation of NPs by cancer cells and the unpredictable magnetic behavior of NPs...
The soft magnetic properties in iron-based nanocrystalline alloys have generally been achieved through the addition of nonmagnetic additives, but this has the unwanted effect of reducing the saturation magnetization. In a recent advance, it was shown that magnetically soft nanostructured alloys could be prepared from a simple, binary Fe-B amorphous...
Magnetic nanoparticles have been largely proposed as means of technological tools due to its value in different fields, especially in biomedicine. Herein, we present a robust, highly reproducible and low-cost method to obtain superparamagnetic magnetite nanoparticles (MNP-II) of about 15±5 nm diameter by thermal decomposition of [Fe(acac)3] in a on...
A systematic study of the magnetic and structural properties dependence on the particle size was realized. For this, commercial NdFeB powder was separated into five different mean particle sizes using sieves. Besides, from the original powder, eleven samples were also produced by mechanical milling assisted by surfactant, using various milling time...
We present results of the synthesis and characterization of Fe—Co—V high magnetization ferromagnetic nanoparticles (NPs) fabricated by two physical routes: laser ablation in liquid flow and mechanical ball milling. As characterizing techniques, we used dynamic light scattering, X-ray diffraction, transmission and scanning electron microscopy, and m...
Most studies of magnetic nanoparticle-based hyperthermia utilize iron oxide nanoparticles smaller than 20 nm, which are intended to have a superparamagnetic behavior (SP-MNPs). However, the heating power of larger magnetic nanoparticles with non-fluctuating or fixed magnetic dipoles (F-MNPs) can be significantly greater than the one of SP-MNPs if h...
Magnetic hyperthermia has the potential to play an important role in cancer therapy and its efficacy relies on the nanomaterials selected. Superparamagnetic iron oxide nanoparticles (SPIONs) are excellent candidates due to the ability of producing enough heat to kill tumor cells by thermal ablation. However, their heating properties depend strongly...
Nd-xZrxFe10Si2 alloys have been prepared in the tetragonal ThMn12-type structure by arc-melting and melt spinning and then nitrogenated to improve their magnetic properties. For x = 0.4 and 0.6 the Curie temperature and magnetic anisotropy fields increases from 280 to 300 °C to about 390 °C and from 2.8 to 3 Tesla to 4.5–5 Tesla respectively. The s...
A new hybrid inorganic-organometallic salt has been obtained from the reaction of the Keggin-type silicotungstate anion with ferrocene in a water/methanol mixture as a result of the partial oxidation of ferrocene molecules to ferrocenium cations. Single-crystal X-ray diffraction analysis reveals the presence of four ferrocenium (FeIII) cations and...
The effect of combined mechanical and thermal treatments in the magnetostructural properties is studied in a Ni-Mn-Sn metamagnetic shape memory alloy, by X-ray diffraction, powder neutron diffraction, calorimetry, magnetometry and ¹¹⁹Sn Mössbauer spectroscopy. A Ni50Mn35Sn15 alloy has been mechanically milled and then annealed at different temperat...
We report a thorough structural and magnetic study of Fe3Sn produced either by solid state reaction or by mechanical alloying in order to figure out which of the two techniques is most suitable for obtaining the purest Fe3Sn alloy. Solid state reaction of Fe and Sn starting powders results in a pure sample (100%) of Fe3Sn. The extraordinary purity...
We report the study of Zr1-xCexFe10Si2 (x = 0.0, 0.3 and 0.6) compounds, with tetragonal ThMn12 structure, by means of neutron diffraction and Mössbauer spectroscopy to understand the role of Ce in the increasing magneto-crystalline anisotropy. Fitting of the ⁵⁷Fe Mössbauer spectra to the three Fe atomic positions, namely 8i, 8j and 8f, indicate th...
While suitable texture has been developed in Nd2Fe14B/α-Fe nanocomposites via thermomechanical processing methods such as die upsetting by incorporating low melting point eutectic Nd-Cu additives, significant grain coarsening occurs during this process due to the high temperature and long timescales involved, resulting in a loss of exchange couplin...
In this work, we report the effects of partial substitution of Ce by Sm in CeFe9Co2Ti alloys on their magnetic and structural properties. The alloys were prepared in bulk and melt-spun ribbons. The alloys present the ThMn12 phase in the full range of substitutions, and reach anisotropy fields above 8 T for the best alloy. After heat treatment, melt...
Lignin conversion processes produce carbon rich residues1,2 that can be converted into valuable materials such as magnetic activated carbons (MACs). Such lignin-derived MACs can be further used as functional substrates for hydrotreating NiMo catalysts. In this work, we studied the activity of different NiMo-MACs for the catalytic conversion of lign...
Discontinuous multilayer (DML) thin films, which consist of nano-granular metals (NGMs) embedded in a dielectric matrix, have attracted significant interest as engineered plasmonic metamaterials. In this study, a systematic layer-by-layer deposition of three-dimensional sub-wavelength periodic plasmonic DML structures via the radio frequency sputte...
The influence of defects and local stresses on the magnetic properties and martensitic transformation in Ni50Mn35Sn15 is studied at macroscopic and atomic scale levels. We show that both the structural and magnetic properties of the alloy are very sensitive to slight microstructural distortions. Even though no atomic disorder is induced by milling,...
In this work, we present a complete study of the influence of Nb and Cu addition on the crystallization behavior of Nd-lean Nd–Fe–B melt-spun alloys. Alloys with compositions Nd10−x−y Fe84B6Nb x Cu y (x = 1, y = 0 and x = 0.5, y = 0.5) were melt-spun at different wheel speeds (15–40 m s−1) to obtain samples in amorphous, highly disordered and nanoc...
D assemblies of magnetic nanoparticles are of great potential for designing novel nanostructured materials with enhanced collective magnetic properties. In that challenging context, a new assembly strategy is presented to prepare chains of magnetic nanoparticles that are well-defined in structure and in spatial arrangement. The 1D assembly of iron...
High-performance Mn-rich P2-phase Na2/3Mn0.8Fe0.1Ti0.1O2 is synthesized by a ceramic method, and its stable electrochemical performance is demonstrated. 23Na solid-state NMR confirms the substitution of Ti4+ ions in the transition metal oxide layer and very fast Na+ mobility in the interlayer space. The pristine electrode delivers a second charge/d...
The current study reports on the prepara-tion of 10–13 nm ZnO nanoparticles homoge-neously doped with Fe 2+ ions ((Zn 0.97 Fe 0.03)O) and the manipulation of their ferromagnetic response at room temperature with an appropriate post-processing. The homogeneous spatial distribution of iron is studied at atomic column level through high-resolu-tion tr...
Thiol-capped Au nanoparticles with a permanent magnetic moment were prepared using a new two-step chemical process. The two-step process opens up a new facet of fundamental research on the mechanism of the induced ferromagnetism in intrinsically nonmagnetic materials by investigating independently the nano-size and chemical effects on the magnetism...
The aim of this work is to develop a new low-T-c magnetic implant material with high heat generation and self-controlled capability for hyperthermia treatments based on a new class of Mn1+xTixFe2-2xO4 spinel ferrite. Magnetic Mn1+xTixFe2-2xO4 ferrites were successfully prepared by a coprecipitation technique. The structural and magnetic properties...
An approach to the design of a suitable system for technological applications, such as magneto-rheological fluids with controllable performance, showing high saturation magnetization and low coercivity and remanence, is presented. This approach is based on the synthesis of stable iron nanoparticles with a relatively thick polymeric coating -the non...
An approach to the design of a suitable system for technological applications, such as magneto-rheological fluids with controllable performance, showing high saturation magnetization and low coercivity and remanence, is presented. This approach is based on the synthesis of stable iron nanoparticles with a relatively thick polymeric coating -the non...
Fe-rich Fe–Al alloys present a large variety of magnetic behaviors and mechanical deformation of those alloys affects largely their magnetism. At room temperature alloys can be ferromagnetic, paramagnetic or show magnetic inhomogeneities, and at low temperatures spin-glass and re-entrant spin-glass phenomena have been found. Unfortunately, the mech...
In this work, it is demonstrated that capping with trioctylphosphine oxide (TOPO) induces a ferromagnetic response in free-standing ZnO nanoparticles upon calcination without the necessity of metallic doping. Samples were synthesized by precipitation of zinc acetate solutions in a basic medium followed by capping with TOPO and heat treatment in sta...
The correlation between the x-ray absorption spectra and the magnetic properties for Al doped ZnO nanostructures prepared by mechanical alloying has been studied in order to clarify the origin of the
room-temperature ferromagnetism in the Al doped ZnO nanostructures. Room-temperature ferromagnetism is induced in nanostructured ZnO-Al powders by mi...
We study the influence of different Al/Si ratios on the magnetic and structural properties of mechanically disordered powder Fe75Al25−xSix alloys. The results indicate that addition of Si to binary Fe-Al alloys makes the disordering more difficult. The study of the hyperfine fields indicates that there is an inversion of the behavior of the hyperfi...
We show that bulk gold (Au) exhibits temperature-independent paramagnetism in an external magnetic field by x-ray magnetic circular dichroism spectroscopy at the Au L(2) and L(3) edges. Using the sum-rule analysis, we obtained a magnetic moment of 1.3 × 10(-4) μB/atom in an external magnetic field of 10 T and a paramagnetic susceptibility of 8.9 ×...
The magnetic and electrical transport properties of regioregular poly(3-hexylthiophene)-capped Au nanoparticles (NPs) doped with iodine have been investigated to clarify the effectiveness of conductive polymer capping on the induction of ferromagnetism in Au. The room-temperature magnetization curve of the undoped polythiophene-capped Au NPs exhibi...
Dodecanethiol capped Ag nanoparticles (NPs) have been independently synthesized by the well-known Brust method under the same physical-chemical conditions. The obtained NP present similar sizes (∼2 nm ) but different magnetic behaviors. The extended x-ray absorption fine structure analyses at the K -edge of Ag did not reveal any noticeable structur...
The magnetic and optical properties of regioregular poly(3-hexylthiophene)-capped Au nanoparticles (NPs) have been investigated in order to clarify the effectiveness of polythiophene capping on the induction of ferromagnetism in Au. The room-temperature magnetization curve of the polythiophene-capped Au NPs exhibits a clear hysteresis behavior with...
The origin of the room-temperature ferromagnetism (RTF) in ZnO-based dilute magnetic semiconductors remains controversial. We experimentally demonstrate here that it is possible to induce RTF in ball milled (ZnO)1−x/Alx without any ferromagnetic dopant. Our work shows that RTF in (ZnO)1−x/Alx (x = 0–0.5) can be realized simply by milling a mixture...
Zirconium oxide inclusion in Bi2212 superconducting tapes and bulks was studied as possible artificial pinning centers (APC). In order to analyze the zirconium oxide APC addition in Bi2212 samples, magnetization measurements were performed in bulks and transport properties measurements were performed on tapes. In magnetization measurements, the cri...
Different dodecanethiol capped Au nanoparticles (NP) with similar sizes (∼2 nm ) but different ferromagnetic signals at room temperature have been investigated by means of x-ray absorption spectroscopy at the Au L<sub>3</sub> -edge. The reversion of the x-ray magnetic circular dichroism signal with the change of sign of the external applied magneti...
Evolution of static magnetic properties of a set of enhanced γ-Fe2O3/SiO2 nanocomposites with different iron concentration has been studied on the basis of their corresponding hysteresis loops, zero-field/field-cooled (ZFC/FC) magnetization curves and transmission electron microscopy images. The lack of coercivity in all compositions, as well as th...
Neutron diffraction patterns were acquired in situ from a melt-spun amorphous Fe74Nd5B18Cr3 alloy upon heating at constant rates of 1.7×10-2 and 1.3 K/s. The diffraction patterns revealed the following decomposition reaction with two different intermediate routes: amorphous-->Fe3B/Nd2Fe23B3 (at 1.7×10-2 K/s) or Fe3B/Nd2Fe14B (at 1.3 K/s)-->Fe/Fe2B/...
The field-induced magnetic anisotropy (Ku) and the hyperfine interactions in nanocrystalline Fe94−xNb6Bx (x=10, 12, and 14) alloys have been investigated with particular attention paid to the origin of Ku in the bcc-Fe/amorphous soft magnetic nanostructures. The 57Fe Mo¨ssbauer spectra from the Fe–Nb–B alloys suggest that the solute content in the...
The crystallization process of mechanically alloyed Fe75Zr25 metallic glasses is investigated by means of both thermo-magnetization and in situ neutron powder thermo-diffraction experiments in the temperature range 300–1073 K. It was found that the crystallization takes place in a two-step process, involving firstly the appearance of metastable Fe...
With the aim of studying the relationship between structure and magnetism of Fe1-xAlx alloys, annealed and as-crushed samples with 0.25 <= x <= 0.425 been studied. X-rays and Mossbauer spectra show that the nearest neighborhood of each Fe atom plays a major role when determining the magnetic behavior of each Fe atom. In fact, these techniques allow...
In the present paper we report the magnetic characterization of silver-iron oxide nanocomposite obtained by the chemical microemulsion method. TEM images and X-ray diffractograms show that the nanocomposite consists of Ag nanoparticles of ∼ 7 nm surrounded by a quasiamorphous matrix. The ZFC–FC curves and Mössbauer spectra obtained at different tem...
To clarify the influence of the coherent field-induced anisotropies (Ku) on the exchange softening effect in magnetic nanostructures, the soft magnetic properties of both bcc-Fe and D03-Fe(Si)-based nanocrystalline alloys annealed under static and rotating fields were surveyed. The random anisotropy model with Ku predicts that the grain size (D) de...
A representative nanocomposite made of ferrimagnetic [gamma]-Fe2O3 and antiferromagnetic [alpha]-Fe2O3 nanoparticles with estimated weight fractions of ~90 and ~10%, respectively, and grown in transparent silica xerogels has been characterized by Mössbauer spectroscopy with respect to the temperature. The changes of the hyperfine parameters of the...
A description of the growth processes of maghemite ([gamma]-Fe2O3) nanoparticles in a silica matrix (SiO2) synthesized under a classic sol-gel method is proposed in order to explain the observed magnetic behavior at different stages of the sample heat treatment. Analytical electron microscopy studies reveal the appearance of large iron oxide aggreg...
Ever since the first studies of magnetic Au nanoparticles (NPs) were published, few have been the element specific techniques or microscopic probes used to unequivocally determine the origin of their novel magnetic behavior. Here, we report muon spin relaxation (μSR) results of dodecanethiol capped Au NPs, showing the inherent signature of an order...
