Low Magnetic Moment Research Articles

Ab initio prediction of coexistence of two magnetic states in Mn[formula omitted]Sn ([formula omitted]Sc, Ti, and V) Heusler alloys under applied pressure

The structural, magnetic and electronic properties of Mn2YSn (Y=Sc, Ti, and V) Heusler alloys under applied hydrostatic pressure are studied by the first-principle calculations and Monte Carlo simulations. We find that two magnetic reference states with low and high magnetic moment at the low and high crystal lattice volume, respectively, can coexist together due to the almost equal energy under applied pressure of 3.4, −2.9 and −3.25 GPa for Mn2ScSn, Mn2TiSn, and Mn2VSn, correspondingly. The positive/negative pressure correspond to the uniform lattice contraction/expansion. We show that for all compounds, the low magnetic state (LMS) is characterized by the almost half-metallic behavior and it is maintained against hydrostatic pressure. However, the electronic structure of the high magnetic state (HMS) takes on a metallic character. For HMS, the magnetic exchange parameters and Curie temperatures are found to be sufficiently larger values as compared to those of LMS. To identify stable phases at given pressures, the phase diagrams are constructed. The pressure-induced switching mechanism between almost half-metallic and metallic states with different magnetization is proposed.

Influence of coordination structure of Fe-585DV/NxC4-x on the electrocatalytic performance of oxygen reduction reactions.

Fe-N-C material, known for its high efficiency, cost-effectiveness, and environmental friendliness, is a promising electrocatalyst in the field of the oxygen reduction reaction (ORR). However, the influence of defects and coordination structures on the catalytic performance of Fe-N-C has not been completely elucidated. In our present investigation, based on density functional theory, we take an Fe adsorbed graphene structure containing a 5-8-5 divacancy (585DV) defect as a research model and investigate the influence of the coordination number of N atoms around Fe (Fe-NxC(4-x)) on the ORR electrocatalyst behavior in alkaline conditions. We find that the Fe-N4 structure exhibits superior ORR catalytic performance than other N coordination structures Fe-NxC4-x (x = 0-3). We explore the reasons for the improved catalytic performance through electronic structure analysis and find that as the N coordination number in the Fe-NxC(4-x) structure increases, the magnetic moment of the Fe single atom decreases. This reduction is conducive to the ORR catalytic performance, indicating that a lower magnetic moment is more favorable for the catalytic process of the ORR within the Fe-NxC(4-x) structure. This study is of great significance for a deeper understanding of the structure-performance relationship in catalysis, as well as for the development of efficient ORR catalysts.

Unconventional Spin State Driven Spontaneous Magnetization in a Praseodymium Iron Antimonide.

Consolidating a microscopic understanding of magnetic properties is crucial for a rational design of magnetic materials with tailored characteristics. The interplay of 3d and 4f magnetism in rare-earth transition metal antimonides is an ideal platform to search for such complex behavior. Here the synthesis, crystal growth, structure, and complex magnetic properties are reported of the new compound Pr3 Fe3 Sb7 as studied by magnetization and electrical transport measurements in static and pulsed magnetic fields up to 56T, powder neutron diffraction, and Mößbauer spectroscopy. On cooling without external magnetic field, Pr3 Fe3 Sb7 shows spontaneous magnetization, indicating a symmetry breaking without a compensating domain structure. The Fe substructure exhibits noncollinear ferromagnetic order below the Curie temperature TC ≈380 K. Two spin orientations exist, which approximately align along the Fe-Fe bond directions, one parallel to the ab plane and a second one with the moments canting away from the c axis. The Pr substructure orders below 40K, leading to a spin-reorientation transition (SRT) of the iron substructure. In low fields, the Fe and Pr magnetic moments order antiparallel to each other, which gives rise to a magnetization antiparallel to the external field. At 1.4K, the magnetization approaches saturation above 40T. The compound exhibits metallic resistivity along the c axis, with a small anomaly at the SRT.

The effect of C and (Er, Sm, Eu)2O3 doping and high isostatic pressing on superconducting properties of MgB2 phase and volume of cylindrical MgB2 ceramic samples

We present our research on the influence of pressure on the synthesis of the MgB2 phase and, consequently, on the superconducting properties of the MgB2 system. We investigated undoped, C-doped, and double-doped, i.e. C and Re2O3 Re = Sm, Eu, Er), MgB2 samples. We conducted comparative studies of critical temperature, irreversibility field, critical current and pinning force for ceramic samples annealed at ambient pressure and 1 GPa. Heat treatment under high isostatic pressing (HIP) of 1 GPa reduced the volume of the undoped MgB2 cylinder by 40%. This significantly increases the density, homogeneity and number of connections between the grains, and also eliminates voids in the undoped material. However, we did not observe any reduction in the volume of C-doped and double-doped MgB2 cylinders. Our research shows that the critical parameters of the MgB2 superconductor can be increased more effectively by doping C and the HIP process than by double doping C with Er, Sm or Eu and the HIP process. The HIP process improved the efficiency of pinning centers created by magnetic admixtures with a low magnetic moment (Sm and Eu), but on the other hand, reduced this efficiency for admixture with a high magnetic moment (Er).

Charge Radii of ^{55,56}Ni Reveal a Surprisingly Similar Behavior at N=28 in Ca and Ni Isotopes.

Nuclear charge radii of ^{55,56}Ni were measured by collinear laser spectroscopy. The obtained information completes the behavior of the charge radii at the shell closure of the doubly magic nucleus ^{56}Ni. The trend of charge radii across the shell closures in calcium and nickel is surprisingly similar despite the fact that the ^{56}Ni core is supposed to be much softer than the ^{48}Ca core. The very low magnetic moment μ(^{55}Ni)=-1.108(20) μ_{N} indicates the impact of M1 excitations between spin-orbit partners across the N,Z=28 shell gaps. Our charge-radii results are compared to abinitio and nuclear density functional theory calculations, showing good agreement within theoretical uncertainties.

A first-principles study on the effect of Cr, Mn, and Co substitution on Fe-based normal- and inverse-Heusler compounds: Fe3−xYxZ (x=0, 1, 2, 3; Y= Cr, Mn, Co; Z=Al, Ga, Si)

First-principles calculation has become one of the most reliable approaches in predicting structural, electronic, and magnetic properties for material applications. Alloys in Heusler structures have also attracted much attention recently since they can be easily synthesized and provide interesting properties for future spintronic applications. In this work, we investigate a series of Fe-based Heusler compounds Fe3−xYxZ (x = 0, 1, 2, 3; Y= Cr, Mn, Co; Z= Al, Ga, Si) with L21- and XA-type structures using first-principles calculations based on density functional theory. According to formation energy calculations and mechanical property analysis, most of the studied Heusler compounds are thermodynamically stable and could be synthesized experimentally. The Co substitution leads Fe3−xCoxZ to a ferromagnetic ground state like Fe3Z with a strong magnetization ranging from 4 to 6 μB/f. u. While replacing Fe with Cr or Mn, the exchange coupling between Cr (Mn) and its neighboring atoms generally tend to be anti-parallel. Among the antiferromagnetic compounds, Mn3Al and Mn3Ga are antiferromagnetic half metal while Mn3Si is ferrimagnetic half metal. These rarely found type of half metals with low magnetic moment and high spin polarization at the Fermi level are important for low energy consumption spintronic applications. The estimated Curie temperatures for Mn3Al, and Mn3Si and Co2FeSi (XA) are in good agreement with previously theoretical values, while for Fe3Al and Fe3Si, they are in good agreement with previous experimental results. The good consistency in Curie temperature demonstrates high reliability of our predictions based on first-principles calculations. As for the topological property aspect, we predict Fe2CrAl and Fe2MnAl as the 3-dimensional Weyl semimetal. Furthermore, Fe2CrSi is predicted to be the magnetic nodal-line semimetal. Interestingly, our mechanical property analysis demonstrates that Co3Si and Fe2CoSi (L21) exhibit ultraelastic metal behavior, which is of high potential in advanced mechanical industry. This work suggests that Heusler compounds are excellent candidates for future spintronics as well as for high-performance ultraelastic metals.

Development of Precise Shimming Technique With Materials Having Low Saturation Magnetization

Magnetic field shimming using low saturation magnetization material was tested to realize spatial magnetic field homogeneity of less than 1 ppm. The magnetic moment per unit mass were measured for three candidates, that is, Nickel, magnetic fluid and magnetic putty, and it was verified that those have low magnetic moments suitable for precise shimming below 1 ppm. The magnetic shimming test was performed using MRI magnet for MuSEUM experiment at 1.2 T with iron plates, Ni thin plates and magnetic putty. The magnetic shimming with iron plates was conducted employing the two step shimming scheme, and the homogeneity could be reached to 0.29 ppm peak-to-peak (ppm <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$_\text{pp}$</tex-math></inline-formula> ) after six shimming trials. Then, the precise shimming was carried out with Ni thin plates and magnetic putty, and the homogeneity could be reached to 0.16 ppm peak-to-peak with Nickel and 0.17 ppm <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$_\text{pp}$</tex-math></inline-formula> with magnetic putty. No deformation of putty in the magnetic field was observed even after two months. The magnetic field monitoring for two months showed that magnetic field strength and homogeneity largely depended on the temperature, and the temperature of the magnet room has to be controlled within <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$\pm$</tex-math></inline-formula> 0.35 degC under the circumference condition of the shimming test in order to keep the magnetic field change and the homogeneity within <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$\pm$</tex-math></inline-formula> 0.1 ppm. In addition, it is showed that the refilling of LHe in the MuSEUM magnet system should be performed once per 29 days The practical implementation method for magnetic putty was suggested for the existing magnet system by using plastic spacers with holes.

Discontinuity in the Electronic Structure and Magnetic Order of β-Co1+xGa1-x.

The present work reports on the calculated electronic and magnetic structure of the binary Co-Ga system at high Co content. -CoGa adopts a simple cubic CsCl type structure. Well-ordered CoGa does not exhibit collective magnetism but is a paramagnetic, metallic compound. Neither Co nor Ga deficiency induces magnetic order; however, ferromagnetism is observed for Co-Ga anti-site disorder. The magnetic moment per cell increases by up to approximately 1.2 in the completely disordered body-centered cubic structure. With increasing Co content, CoGa maintains the CsCl type structure and becomes ferromagnetic. Most importantly, a discontinuity of the magnetic order with composition is observed at about 10% excess Co, where a change from a low magnetic moment state to a high moment state is observed. This is accompanied by a change in the electronic structure and transport properties. The discontinuity is forced by the increasing exchange splitting related to the localized moment of the additional Co atoms that replace Ga. Subsequently, the magnetic moment increases continuously up to 2.5 for . For , the structure changes to a face-centered cubic structure with random site occupation and the magnetic moment further increases. Above the magnetic discontinuity, the Curie temperature increases linearly with the Co content from the onset of ferromagnetism, until it reaches its maximum in pure Co.

Opportunities for nitrogen-vacancy-assisted magnetometry to study magnetism in 2D van der Waals magnets

Exploring and understanding magnetism in two-dimensional (2D) van der Waals (vdW) magnetic materials present a promising route for developing high-speed and low-power spintronics devices. Studying their magnetic properties at the nanoscale is challenging due to their low magnetic moment compared to bulk materials and the requirements of highly sensitive magnetic microscopy tools that work over a wide range of experimental conditions (e.g., temperature, magnetic field, and sample geometry). This Perspective reviews the applications of nitrogen-vacancy center (NV) based magnetometry to study magnetism in 2D vdW magnets. The topics discussed include the basics, advantages, challenges, and the usage of NV magnetometry.

A DFT Study on the Activity Origin of Fe-N-C Sites for Oxygen Reduction Reaction.

Iron-nitrogen-carbon materials have been known as the most promising non-noble metal catalyst for proton-exchange membrane fuel cells (PEMFCs), but the genuine active sites for oxygen reduction reaction (ORR) are still arguable. Herein, by the thorough density functional theory investigations, we unravel that the planar Fe2 N6 site exhibits excellent ORR catalytic activity over both FeN3 and FeN4 sites, and the potential-determining step is determined to be the *OH hydrogenation step with an overpotential of 0.415 V. The ORR activity of Fe2 N6 site originates from the low spin magnetic moment (1.11 μB ), which leads to high antibonding states and low d-band center of the Fe center, further leads to weak binding strength of *OH species. The density of FeN4 sites only has little influence on the ORR activity owing to the similar interaction between active site and intermediates in ORR. Our research sheds light on the activity origin of iron-nitrogen-carbon materials for ORR.

Structural, dielectric and magnetic properties of Nickel-Chromium substituted Magnesium ferrites, Mg1–Ni Fe2-xCrxO4 (0 ≤ x ≤ 0.7)

In this paper, we report the structural, dielectric, and magnetic properties of Mg1–xNixFe2-xCrxO4 (0 ≤ x ≤ 0.7) ferrites synthesized via a solid-state process. The XRD patterns indicated forming a single-phase cubic spinel structure with a Fd-3 m space group for all samples with crystallite sizes ranging from 31.63 to 73.52 nm. Scanning Electron Microscopy (SEM) showed the formation of dense microstructure with an average grain size of 129.2 to 414 nm. The elemental analysis (EDS) confirmed the chemical purity for all the prepared samples. The saturation magnetization (Ms) was found to be maximum for the composition x=0.3, after which it decreased due to the lower magnetic moment of Cr3+ ion (3 μB) than that of Fe3+ ion (5 μB). The samples' maximum magnetic saturation and coercivity are 62.04 emus/gm and 6.8 KOe, respectively. The measured sample's dielectric constant (ε') and loss tangent (tan δ) decreased with the increased applied field frequency, showing normal behavior. This can be explained in light of Maxwell–Wagner interfacial polarization and hopping of electrons between the Fe2+ ↔ Fe3+ ions. Thus, the synthesized Ni-Cr substituted MgFe2O4 ferrite material is promising for recording materials.

Synthesis, characterization, and multifunctional applications of novel metal complexes based on thiazolylazo dye

AbstractHerein, a novel ligand, namely, N,N‐dimethyl‐4‐((4‐(pyridin‐2‐yl)thiazol‐2‐yl)diazenyl)aniline, and its solid Mn (II), Co (II), Ni (II), and Cu (II) complexes have been synthesized and characterized. The photophysical properties of the thiazolyl azo ligand, L, have been investigated in various solvents of different polarities. The absorption and fluorescence maxima of the ligand show a strong dependence on the solvent polarity. The metal ions sensing response to Mn (II), Co (II), Ni (II), and Cu (II) ions were also investigated in ethanolic solutions. The novel solid complexes of hexacoordinate Mn (II), Co (II), Ni (II), and Cu (II) of the ligand have the molar ratio 2:1 (M:L) and general chemical formula [M2(L)(H2O)4Cl4]·nH2O. The presence of metal–metal interaction was proved by the low magnetic moment values μeff of metal complexes. The UV–Vis spectra of the ligand and its metal complexes displayed bands characteristic to different types of transitions inside the molecules. The metal complexes show additional absorption bands of very low intensity around 650–690 nm attributed to d–d transitions within the metal ion indicating octahedral geometry. The geometry of the ligand and its complexes was also theoretically confirmed using the DMOL3 program and density functional theory (DFT). The free ligand and its metal complexes have been studied for their DNA‐binding properties using steady‐state absorption and emission techniques. They demonstrated successful binding properties against CT‐DNA in an intercalative mode. Additionally, the ligand and its metal complexes have also been successfully applied to polyester fabrics as disperse dyes. Multifunctional properties such as color representation, colorimetric data (L*, a*, b*, C*, h*, K/S), and fastness properties of the dyed samples have been discussed and evaluated in detail. These dyes have proven their efficiency in dyeing polyester fabrics, as they give satisfactory results in fastness properties, colorimetric data. Moreover, the antioxidant and antitumor activities for the synthesized compounds were evaluated.

Effects of Bi doping on structural and magnetic properties of cobalt ferrite perovskite oxide LaCo0.5Fe0.5O3

Literature reports on magnetic transition of LaFe0.5Co0.5O3 are highly ambiguous. The present study is an endeavour to address that particular issue of this ferrite perovskite. Here we report the low temperature sol-gel synthesis of pure and Bi-doped La1-xBixFe0.5Co0.5O3 (x = 0, 0.1 & 0.2) perovskites. All the samples were characterized by powder X-ray diffraction, X-ray photoelectron spectroscopy, field emission scanning electron microscopy, energy dispersive X-ray (EDX) analysis and magnetization studies. LaFe0.5Co0.5O3 crystallizes in a single phase rhombohedral (R-3c) structure. Substitution of Bi at the A-site results in structural transition. La0.9Bi0.1Fe0.5Co0.5O3 exhibits mixed rhombohedra (R-3c) and orthorhombic (Pbnm) phases, whereas La0.8Bi0.2Fe0.5Co0.5O3 is single phase orthorhombic (Pbnm). Favourable grain growth and good crystallinity observed in Bi doped samples are possibly due to the low melting temperature of Bi containing La1-xBixFe0.5Co0.5O3. EDX analysis confirms the chemical homogeneity of the samples. XPS studies and bond valence sum calculations confirm the nominal cationic oxidation states of the ions. Magnetization measurements reveal the weak ferromagnetic nature of La1-xBixFe0.5Co0.5O3 (x = 0, 0.1 & 0.2) which is associated to the canted antiferromagnetic structure. The magnetically active subsystem of Fe3+ ions are responsible for weak ferromagnetism which is explained by the antisymmetric Dzyaloshinskii–Moriya interaction, whereas the Co3+ ions remain predominantly in the low spin state. The increase in magnetic transition and the lower magnetic moment with an increase in Bi content can be related to the weakening of Dzyaloshinskii–Moriya interaction due to structural modification and local lattice distortion associated to the stereochemically active 6s2 lone pair electrons of the Bi3+ ions. Our results confirm the high structure sensitivity of magnetic properties of cobalt ferrite perovskite.

Enhanced performance of Bi2Te3-based thermoelectric materials by incorporating Bi2Fe4O9 magnetic nanoparticles

Thermoelectric (TE) materials have been extensively investigated to solve the energy crisis and alleviate environmental pollution. Currently, n-type and p-type Bi2Te3 based are the only commercialized TE materials. However, their application has been severely limited by the low TE figure of merit (ZT) of p-type Bi2Te3-based TE materials. Here, we demonstrate that the TE performance of p-type materials could be improved by incorporating Bi2Fe4O9 magnetic nanoparticles. Bi2Fe4O9 magnetic nanoparticles could effectively scatter low-energy carrier and improve the carrier quality. The synergistic effect of boundary scattering and magnetic particles scattering lead to the increase of Seebeck coefficient and decrease of thermal conductivity. Finally, the maximum ZT value 1.1 is obtained at 393 K, which is 13% higher the pure sample. The average ZT value of the nanocomposite consisting Bi2Fe4O9 magnetic nanoparticles is 0.98 in the temperature range of 303–483 K, exhibiting an increase of 11%. Overall, the results indicate that magnetic nanoparticles with low saturation magnetic moment have positive effect on the performance of TE materials.

Magnetic force microscopy contrast formation and field sensitivity

The magnetic force microscope (MFM) is an established experimental tool for imaging stray fields with high spatial resolution and sensitivity. The MFM contrast can however contain contributions from the sample topography, variations in the surface Kelvin potential and magnetic contributions arising from grain-to-grain variations of the areal density of the magnetic moment, apart from the contrast generated by the micromagnetic pattern of the sample. Differential imaging techniques can be used to disentangle these contrast contributions. The calibration of the response of the MFM tip on different spatial wavelengths of the field allows a quantitative determination of the magnetic vector field in the plane parallel to the sample surface scanned by the tip. Generally, the tip becomes less sensitive for smaller spatial wavelengths. Obtaining a high spatial resolution thus requires a high measurement sensitivity that can be obtained by MFM operation in vacuum and by using high-quality factor cantilevers. As a result, field sensitivities better than 80μT/Hz can be obtained, even with low magnetic moment tips.

Localization of rare earth ions in an inhomogeneous magnetic field toward their magnetic separation

Efficient extraction and recycling methods are an important issue for rare earth elements (REE). The significant differences in their magnetic moments make magnetic separation a promising step. Although the magnetic field gradient manipulation of ions seemed to be impossible, the robust enrichment of some paramagnetic RE ions was found in the vicinity of the magnet. The studies in recent years resolved the physical paradox of why, despite the Brownian motion of the ions, there is a reproducible enrichment of RE ions in magnetic field gradients. The existence of trigger process and energy barrier was proved. However, these studies usually used only high paramagnetic ions, e.g., Dy(III) or Ho(III). This work verifies the theory of the possible magnetic separation for 8 different rare earth ions, respectively. For this purpose, concentration distribution in rare earth chloride solutions were measured using a Mach-Zehnder interferometer. The magnetic field was assured by a Halbach configuration to enhance the effect. The results show the classification of RE solutions into 2 classes: Class I contains the REs with low magnetic moment, whereas Class II includes the REs of high magnetic moment. Only the latter group shows the enrichment of ions in the vicinity of the magnet which encourages the implementation of magnetic separation into existing hydrometallurgical technology to enhance the selectivity of REE.

Investigation on magnetic properties of mechanically alloyed τ-MnAlC with Fe addition

The influence of Fe addition on thermal stability, crystallography, and magnetic properties of τ-Mn51Al47C2 was investigated. Alloys with composition Mn51-xFexAl47C2 (x = 0, 0.5, 1, 2, and 4) were synthesized by mechanical alloying method. High purity of τ-Mn(Fe)AlC up to 98% could be obtained after 10 h of milling, then annealed at 1050 °C for 1 h, and followed by an aging process at appropriate temperatures from 515 to 540 °C for 50 min. It was found that the thermal stability of both ε and τ phases was enhanced by the addition of Fe up to 4 at.% into MnAlC alloy through a shifting of ε-to-τ transformation temperature to high temperature region and a reduction in c/a ratio of Fe doped τ-MnAlC compared to iron free τ-MnAlC. While the magnetization and Curie temperature of Fe doped τ-MnAlC showed a reduction compared to iron free τ-Mn51Al47C2, coercivity seems not to be significantly affected. Ab initio calculation showed a lower magnetic moment of Fe (μFe = 1.77 μB) compared to Mn (μMn_average = 2.36 μB) in τ-Mn(Fe)AlC when Fe substituted Mn position at 1a site.

Structural aspects and magnetic properties of Nd3+ doped nickel-zinc ferrites

Magnetic properties and structural analysis of Nd(Neodymium) doped Ni0.65Zn0.35Fe2O4 using XRD, Rietveld Analysis, FTIR Spectroscopy and VSM are reported.Confirmation of secondary phase formation with increased Nd content is established. Cation distribution for neodymium substituted nickel-zinc ferritesis proposed by considering the deficiency of Fe3+ in NiZnFe2O4 due to secondary phase formation of NdFeO3. The quality of present cation distribution was confirmed through close agreement of experimentally calculated lattice constant and Rietveld refinement. Changes in saturation magnetization with increased Nd content are explained on the basis of intensifying effect on energy exchange (inter-sublattice) between Ni–O–Nd and Ni–O–Fe concnerning Fe–O–Fe interaction, effect of replacing lower magnetic moment Nd3+ (3.62 μB) in place of Fe3+ (5 μB) and exchange developed between the cations existing at B-sites due to creation of oxygen vacancies.

Synthesis of FePt Nanoparticles by Photoreduction and Chemical Reduction in Poly(ethyleneimine).

Using poly(ethyleneimine) (PEI) polymer substrates, spherical FePt nanoparticles (NPs) with diameter <10 nm have been synthesized by photoreduction and chemical reduction in aqueous media at room temperature. In the photoreduction approach, PEvI acts as both the template into which the metal ions are coordinated and as a reductant when irradiated by ultraviolet light. In the chemical reduction method, PEI acts as only a template, with NaBH4 as the reductant. The as-prepared NPs were characterized using X-ray diffraction (XRD), transmission electron microscopy (TEM), and vibrating sample magnetometry (VSM). Starting from the same precursor state and relative concentrations, the as-prepared NPs from both methods are spherical, crystalline solid solutions with a chemically disordered face-centered cubic (fcc) structure. The as-prepared NPs from both methods are superparamagnetic with some contribution from a ferromagnetic phase. The photoreduced NPs have broad size distribution of (5 ± 1.0 nm), an expanded lattice (3.913 Å), and relatively lower magnetic moment (0.02 emu/g) compared to the narrower size distribution (4 ± 0.7 nm), shortened lattice (3.890 Å), and a dominant moment (15 emu/g) of the chemically reduced NPs. The difference in the rate of particle formation apparently leads to a low efficiency of FePt NP formation via photoreduction compared to chemical reduction.

Effects of ball milling duration and sintering temperature on mechanical alloying Fe3Si

Fe3Si is under interest as a ferromagnetic electrode of magnetic tunneling junctions (MTJs). Its crystalline structure is important for achieving high device efficiency. This work focuses on mechanical alloying of 3:1 ratio of 99% pure Fe and Si powder mixtures by ball milling and sintering. The mixtures were ball-milled for various durations up to 20 h. Then, they were sintered from 400°C to 800°C for 4 h in Ar. SEM images and particle size analysis show significant reduction in average particle size of the mixtures after ball milling for 20 h. The longer duration of ball milling process promotes powder distribution. It results in agglomerated and smooth samples after sintering. XRD analysis indicates that Fe3Si phase appeared after 5 h of mechanical ball milling without sintering. More peaks of Fe3Si phase present at sintering temperatures higher than 600°C, while Fe2Si phase diminishes. However, the amount of Fe2O3 phase increases when sintering at these high temperatures, which strongly affects the magnetic properties of the samples. Magnetic hysteresis loops measured by vibrating-sample magnetometer (VSM) show lower magnetic moments of these samples. Saturation magnetization of the sample decreases more than 95% when sintered at 800°C, agreeing with high content of Fe2O3.