Magnetization Curves Research Articles

Structural, magnetic, magnetocaloric behavior and magneto-transport, electrical polarization study in 3d based bulk and nano-crystalline multiferroic double perovskite Dy2MnCoO6

In this paper, we report a detailed investigation of the crystal structure, magnetic, magnetocaloric, magneto-transport and electrical polarization properties of a new multiferroic material in the polycrystalline and nanocrystalline form of the Dy2MnCoO6 double perovskite. Both compounds crystallized in the monoclinic structure with P21/n space group. The magnetic properties of both systems are mainly dominant ferromagnetic (FM) and weak antiferromagnetic (AFM). The FM/AFM coupling is related by the competing and combining functions of the radius and the magnetic moments of rare earth ions (i.e. 3d–4f exchange interactions). The reduction of the saturation magnetization in the isothermal magnetization curves can be explained by the existence of anti-phase boundaries and local anti-site defects in the system. Moreover, these materials hold reasonable values of magnetocaloric parameters and the absence of hysteresis makes the system a potential candidate for magnetic refrigeration. These compounds revealed two magnetic phase transitions, according to the appearance of two peaks in the temperature dependence of magnetic entropy change curves. The temperature dependent resistivity data for both the systems display semiconductor nature near room temperature and insulating like behavior at low temperature regime. The variable-range hopping conduction mechanism is used to best understand their transport mechanism. In addition, the electrical polarization loop at low temperature confirms the presence of ferroelectricity for both the studied systems. The decreases polarization under an external magnetic field evidence the weak magnetoelectric coupling. The coexistence of FM ordering with insulating behavior and ferroelectricity at low temperature promises new opportunities and improvements in next generation applications for information storage, spintronic, and sensors.

Quantum magnetism in Fe2Cu2 polymeric branched chains: insights from exactly solved Ising-Heisenberg model

The spin-1/2 Ising-Heisenberg branched chain, inspired by the magnetic structure of three isostructural polymeric coordination compounds [(Tp)2Fe2(CN)6X (bdmap)Cu2(H2O)] ⋅ H2O to be further denoted as Fe2Cu2 (Tp = tris(pyrazolyl)hydroborate, bdmapH = 1,3-bis(dimethylamino)-2-propanol, HX = acetic acid, propionic acid or trifluoroacetic acid), is rigorously studied using the transfer-matrix method. The overall ground-state phase diagram reveals three distinct phases: a quantum antiferromagnetic phase, a quantum ferrimagnetic phase and a classical ferromagnetic phase. In the zero-temperature magnetization curve, two quantum ground states are manifested as intermediate plateaus at zero and half of the saturation magnetization, while the magnetization reaches its saturated value within the classical ferromagnetic phase. The bipartite entanglement between nearest-neighbor Heisenberg spins is more pronounced in the quantum ferrimagnetic phase compared to the quantum antiferromagnetic phase due to a fully polarized nature of the Ising spins. A reasonable agreement between theoretical predictions for the spin-1/2 Ising-Heisenberg branched chain and experimental data measured for a temperature dependence of the magnetic susceptibility and a low-temperature magnetization curve suggests strong antiferromagnetic coupling between nearest-neighbor Cu2+-Cu2+ magnetic ions and moderately strong ferromagnetic coupling between nearest-neighbor Cu2+-Fe3+ magnetic ions in the polymeric compounds Fe2Cu2. A thermal entanglement between nearest-neighbor Cu2+-Cu2+ magnetic ions persists up to a relatively high threshold temperature T ≈ 224 K and undergoes a transient magnetic-field-driven strengthening.

ODF-based model considering compressive stress for modeling the magnetic properties of Grain-oriented electrical steels

Grain-oriented electrical steels (GOES) are widely used in the manufacturing of high efficiency energy conversion systems thanks to their excellent magnetic properties along the rolling direction. Nevertheless, on the one hand, GOES exhibit strong magnetic anisotropy, resulting in distinct magnetic properties regarding the direction of the applied magnetic field to the rolling direction. On the other hand, GOES undergoes changes in their magnetic properties due to the industrial manufacturing process and mechanical constraints during operation. In general, stress, and particularly compressive stress, deteriorates magnetic properties. This paper deals with the modeling of the magnetic behavior of GOES under compressive stress. The orientation distribution function (ODF) based approach recently applied to describe the B-H first magnetization curves of a conventional GOES without stress as well as under applied uniaxial mechanical tensile stress is extended to account for the effect of compressive stress, with different considerations of modeling. The magnetic properties and the sensitivity of the ODF-based model to the magnetization direction as well as to the applied compressive stress are analyzed. Oscillation issues inherent to the ODF-based model are also discussed.

The effect of different temperature rate on sol-gel approach derived M-type hexagonal BaFe12O19 using D-mannose as a fuel: Synthesis, structural, thermal gravimetric and magnetic properties

In this article, we reported that the BaFe12O19 powders were prepared using the effective sol-gel process under different calcination temperatures, i.e., 700–900 °C for 2 h. The structural effects of the temperature rate on the phase formation, morphological and magnetic properties of the as-prepared powders have been analyzed and discussed. The X-ray diffraction pattern confirmed the hexaferrite phase formation at calcined temperature range of 800 °C with no secondary phase and the particles size are about 45 nm–65 nm. The Fourier-transform infrared (FT-IR) spectra show that the intensity frequencies for hexaferrite site stretching were observed at 601 and 443 cm−1 from Fe–O and Ba–O bonds, respectively. The micro-sized flakes morphological structure with particle sizes ranging from 45 to 65 nm by strongly agglomerated powders of the hexaferrite phase is examined through the field emission scanning electron microscopy (FESEM) technique for the good-quality calcined 800 °C. Additionally, the effect of the calcination rates at 800 °C on the material features was analyzed by the energy-dispersive X-ray, X-ray photoelectron spectroscopy (XPS), etc. The magnetic properties, such as saturation magnetization and coercive field of the as-prepared nanomaterials were analyzed using the vibrating sample magnetometry (VSM) technique. The hysteresis loop of the BaFe12O19 nanomaterials calcined at 800 °C for 2 h showed excellent magnetic properties, with a higher saturation magnetization curve of 55.774 emu/g and a coercivity (Hc) of 5079 kOe. The dark brown colored annealed 800 °C nanomaterials can be useful as a ceramic color pigment, which has several industrial applications.

The SF and remanence evaluation of magnetic shields based on SST for low-frequency and degaussing situation

As the dominant shielding functional material, the permalloy sheet primarily determines the static and low-frequency shielding performances of magnetically shielded room (MSR). However, the lack of measurement of shielding sheets for practical use would lead to a non-negligible evaluation error in MSR performance. Therefore, an estimation technique of shielding factor (SF) and the remanence of MSR is proposed in this paper while considering the nonlinear magnetic characteristics of the permalloy sheet tested by a single sheet tester for low-frequency field and degaussing situation (L-D-SST). First, a high-accuracy measurement system, comprising L-D-SST (for exciting magnetic field and sensing the corresponding B and H) and the control system (for applying excitation to L-D-SST and amplifying, filtering, and collecting B and H signals), is established. Weak magnetic fields at low frequencies and decaying alternating demagnetizing field excitations are separately applied to the L-D-SST for basic magnetization curves (BM curves) and an anhysteretic magnetization curve (AM curve) tests. Furthermore, the BM and AM curves are respectively integrated with the FEM algorithm for accurate and reliable estimations of the SF and remanence of MSR in an operational state. In addition, the tested magnetic properties are applied for the optimization of MSR shielding quality.

Effects of Mg Substitution on the Structural with Rietveld Analysis, Magnetic and Magnetocaloric Properties of Ni-Cu-Cd Bulk Ceramics

Bulk ceramics with optimized density are highly prioritized over ferrite nanoparticles to fabricate devices for their optimal magnetic saturation, lower coercivity, and anisotropy, enhanced resistance, etc. To achieve such bulk specimen using Ni0.5-yMgyCu0.2Cd0.3Fe2O4 disc samples are sintered at 1423 K keeping the heating and cooling rate at 10 K and 5 K respectively. In due course, structural as well as theoretical Rietveld analysis, optical, and magnetic properties have been analyzed using these bulk samples. XRD has explored structural properties and after that these values have analyzed with the Rietveld refinement procedure and obtained goodness of χ2 (1–2) value and other parameters such as lattice parameters, crystal structures, cation distribution, and maximum entropy mapping. Surface morphology and grain size have examined from the as-grown surface without further polishing and annealing by electron microscopy and revealed a decreasing trend of grain size 6.1 µm to 4.2 µm. UV–Vis spectroscopy characterization ensured optical properties for bulk as well as nanopowders and the band gap has been found in the range of 1.4 to 1.6 eV and is increasing with Mg content. Magnetic hysteresis loop exhibits a less decreasing nature up to y = 0.3 of magnetic saturation along with the Law of Approach to saturation which compiles magnetic anisotropy. The temperature-dependent magnetization curves exhibit a sharp decreasing value (i.e. dM/dT maximum) at Curie point, decreasing from 630 K to 505 K with increasing Mg content. At.3 T magnetic field the changes in relative cooling power value have been found in the range 53.82Jkg-1 to 37.79Jkg-1 which could be considered as potential for magnetocaloric refrigeration.

Composite "Crosslinked Polyvinyl Alcohol-Magnetite" as a Stimuli-Responsive Matrix for Optical Methods.

The preparation and application of the composite material "crosslinked polyvinyl alcohol-magnetite" as a sensitive matrix for use in digital colorimetry and optical micrometry methods are discussed. The material was synthesized in the form of spherical granules (for micrometry) and thin films (for digital colorimetry). The obtained composites were characterized by the registration of magnetization curves. It was shown that the amount of grown Fe3O4 particles in the polymer gel is in linear dependence with the iron salt concentrations in the impregnating solutions. The composite granules were applied to determining monosaccharides using optical micrometry. The optimal pH value for the total amount of monosaccharides' determination was 8.6. The study of the analytical response of composite granules and films performed with a low limit of detection (7.9 mmol/dm3) of both glucose and fructose and a possibility of the control of high alcohol contention in water media. The granules were used to determine the total carbohydrate content in samples of natural honey and syrups with high fructose contents, while the films were used to control the alcohol content in hand antiseptics. The results obtained are in good agreement with the data provided by the manufacturers.

Quantized magnetic flux in a two-band superconducting condensate with a type-Kagome pinning center lattice

In this work we studied the vortex-configuration in a mesoscopic superconducting square in presence of an external magnetic field H applied parallel to its surface vector. We study the magnetization curves in a complete loop, the magnretic induction and the superconducting-electron density for the sample considering Neumann boundary conditions for the order parameter, via length Gennes extrapolation . The sample presents a pinnin center as a Kagome-type laticce at different critical temperature. We solve the generalized time-dependent Ginzburg-Landau equations for a two-condensate system using the Link-variable method considering a Field-Cooling process. Our results show that the vortices are always located at the pinning centers in non-conventional configurations, due to cuopling used.

Structural and magnetic transformations in the system YBaCo4O7+X (x = 0, 0.1, 0.2)

The modification of magnetic and elastic properties of YBaCo4O7+x (x = 0, 0.1) cobaltite series at a small controlled deviation x = 0, 0.1, 0.2 from stoichiometry has been investigated. The non-stoichiometric cobaltites with x > 0.1 are found to be separated into two structural phases with different values of x under certain synthesis and heat-treatment conditions of the YBaCo4O7+x system (x = 0, 0.1, 0.2). A non-trivial magnetic behavior is observed in stoichiometric YBaCo4O7. Magnetic moment ΔM = MFC–MZFC induced by an external magnetic field (an analog of thermo-residual magnetization) exhibits anomalies at magnetic phase transition temperatures TN1 and TN2 that coincide with Young’s modulus anomalies. Conversely, in the magnetic susceptibility curves taken in the FC and ZFC modes, phase transitions are not discerned. When x deviates from stoichiometry, the ratio between two magnetic ions Co3+/Co2+ changes, the induced moment ΔM increases, and a residual ferromagnetic moment of ∼ 10-2μB appears in the magnetization curves at low temperatures. At a slight deviation from the oxygen stoichiometry in the samples, the structural distortion disappears, and the anomalies in the elastic characteristics near the TN region rapidly diffuse and vanish. It has been found that when YBaCo4O7+x cobaltites deviate from stoichiometry, the evolution of their magnetic properties is similar to that observed at the transition from Y-based to Ca-based cobaltite. Two scenarios of the cobalt subsystem magnetic behavior with an increasing fraction of cobalt Co3+ ions have been discussed.

Stress-induced changes in magnetite: insights from a numerical analysis of the Verwey transition

SUMMARY Magnetic susceptibility behaviour around the Verwey transition of magnetite (≈125 K) is known to be sensitive to stress, composition and oxidation. From the isotropic point (≈130 K) to room temperature, decreasing magnetic susceptibility indicates an increase in magnetocrystalline anisotropy. In this study, we present a model which numerically analyses low-temperature magnetic susceptibility curves (80–280 K) of an experimentally shocked (up to 30 GPa) and later heated (973 K) magnetite ore. To quantify variations of the transition shape caused by both shock and heating, the model statistically describes local variations in the Verwey transition temperature within bulk magnetite. For the description, Voigt profiles are used, which indicate variations between a Gaussian and a Lorentzian character. These changes are generally interpreted as variations in the degree of correlation between observed events, that is between local transition temperatures in the model. Shock pressures exceeding the Hugoniot elastic limit of magnetite ($ \ge $5 GPa) cause an increase in transition width and Verwey transition temperature, which is partially recovered by heat treatment. Above the Verwey transition temperature, susceptibility variations related to the magnetocrystalline anisotropy are described with an exponential approach. The room temperature magnetic susceptibility relative to the maximum near the isotropic point is reduced after shock, which is related to grain size reduction. Since significant oxidation and cation substitution can be excluded for the studied samples, variations are only attributed to changes in elastic strain associated with shock-induced deformation and annealing due to heat treatment. The shocked magnetite shows a high correlation between local transition temperatures which is reduced by heat treatment. The model allows a quantitative description of low-temperature magnetic susceptibility curves of experimentally shocked and subsequently heat-treated polycrystalline magnetite around the Verwey transition temperature. The curves are accurately reproduced within the experimental uncertainties. Further applications for analysing magnetite-bearing rocks seem possible if model parameters, such as for oxidation are included into the model.

Low temperature garnet phase formation in Mn-substituted Y3Fe5-xMnxO12 nanoparticles via citrate combustion synthesis

In this article, we report on the formation of a low-temperature garnet phase in Mn-substituted Y3Fe5-xMnxO12 (x = 0, 0.05, 0.15, and 0.25) nanopowders. We studied the structural, microstructural, static, and dynamic magnetic properties of Mn-substituted Y3Fe5-xMnxO12 (YIG) nanopowders calcined at two different temperatures. The Mn-substituted garnet powders were synthesized using the citrate combustion method followed by calcination at 800 and 1200 °C for 3 h. An increase in Mn substitution (x = 0.15, 0.25) favored the growth of a single garnet phase at low temperatures, even at 800 °C. The lattice constant of these samples ranged from 12.3815 to 12.3679 Å. Microstructural and morphological studies revealed the growth of homogeneous and dense particles, with an average particle size in the range of ∼35–58 nm, close to the single-domain particle size in YIG. Microwave resonance spectra and magnetic hysteresis curves revealed the formation of a ferromagnetic phase in undoped and Mn-doped garnet ferrites at room temperature. The maximum saturation magnetization (26 emu/g) was observed for the sample with Mn content x = 0.05 at 1200 °C, while the largest coercivity (33 Oe) was found for the sample with Mn content x = 0.15 at 1200 °C, among all the samples. The increase in Mn content led to a decrease in peak-to-peak linewidth of FMR spectra from 698.8 to 569.4 G at 800 °C and from 916 to 614.7 G at 1200 °C. This study suggests that Mn substitution in YIG garnet improves structural properties and enhances magnetic anisotropy.

Role of Griffiths phase on magnetocaloric properties and critical behavior of half-doped manganites [La0.5Sr0.5-xCaxMnO3(x = 0, 0.25, 0.5)

In this article, a comprehensive study of the effect of calcium substitution on structural magnetic, magnetocaloric properties, and role of Griffiths phase on magnetocaloric properties of half-doped manganites La0.5Sr0.5-xCaxMnO3(x=0,0.25,0.5)] have been presented. A structural phase transition I4/mcm - Pbnm is observed in the whole series. The system exhibits two magnetic transitions for Ca-00 and Ca-25, whereas only one phase transition is observed for Ca-50. Paramagnetic (PM)-ferromagnetic (FM) transition is observed in the whole series and ferromagnetic (FM) - antiferromagnetic (AFM) phase transition is only observed in Ca-25. Interestingly, short range FM clusters exist in the PM matrix of Ca-50, which is a signature of Griffiths phase (GP). The confirmation of GP has been carried out by performing iso-field magnetization measurements at 200 Oe, 500 Oe, and 1 kOe, respectively. Further magnetocaloric properties have been discussed on the basis of isothermal magnetization curves recorded at certain temperature intervals. Calcium substitution favors the enhancement of magnetic entropy change in the series, especially for Ca-50, a magnetic entropy change of 4.5J/(kgK) with relative cooling power of 180J/kg under 5T magnetic field was observed. Iso-field magnetization and magnetocaloric effect along with critical behavior analysis have been carried out to probe the GP and other inhomogeneities present in the respective series.

Dual-phase superconductivity in high-pressure high-temperature synthesized TaNbZrHfTi

We report on a novel TaNbZrHfTi-based high entropy alloy (HEA) which demonstrates distinctive dual-phase superconductivity. The HEA was synthesized under high pressures and high temperatures starting from a ball milled mixture of elemental metals in a large-volume Paris–Edinburgh cell with P ≈ 6 GPa and T = 2300 K. The synthesized HEA is a phase mixture of BCC (NbTa)0.45(ZrHfTi)0.55 with Tc1 = 6 K and FCC (NbTa)0.04(ZrHfTi)0.96 with Tc2 = 3.75 K. The measured magnetic field parameters for the HEA are lower critical field, Hc1(0) = 31 mT, and a relatively high upper critical field, Hc2(0) = 4.92 T. This dual-phase system is further characterized by the presence of a second magnetization peak, or the fishtail effect, observed in the virgin magnetization curves. This phenomenon, which does not distort the field-dependent magnetization hysteresis loops, suggests intricate pinning mechanisms that could be potentially tuned for optimized performance. The manifestation of these unique features in HEA superconductivity reinforces phase-dependent superconductivity and opens new avenues in the exploration of novel superconducting materials.

Resolving the Interpretation of Magnetic Coercivity Components From Backfield Isothermal Remanence Curves Using Unmixing of Non‐Linear Preisach Maps: Application to Loess‐Paleosol Sequences

AbstractUnmixing of remanent magnetization curves, either isothermal remanent magnetization (IRM) or backfield IRM, is widely used in rock magnetic and environmental magnetic studies to discriminate between magnetic coercivity components of different origins. However, the wide range of physical properties of natural magnetic particles gives rise to an ambiguous interpretation of these components. To reduce this ambiguity and provide a straightforward interpretation of coercivity components in terms of domain state, interactions, and constituent magnetic phases, we combined backfield IRM unmixing with unmixing of nonlinear Preisach maps for two typical mid‐latitude northern hemisphere loess‐paleosol sequences. Both backfield IRM and nonlinear Preisach maps unmixing are based on the same non‐parametric algorithm, and provide similar endmembers (EMs) in the two sections studied. The first EM (EM1) has a low median coercivity (∼21 mT) and is a non‐interacting single domain (SD) magnetite/maghemite of pedogenic origin. The second EM (EM2) has a moderate median coercivity (∼60 mT) and is a mixture of pseudo‐single domain/multidomain, SD magnetite/maghemite and non‐interacting SD hematite, all of eolian origin. The same EM1 found in both sections suggests that this component's grain size and coercivity are independent of pedogenesis intensity. The same EM2 indicates that a similar magnetic population is being transported and deposited, irrespective of the dust source area and loess granulometry. The approach outlined here provides strong evidence that non‐parametric backfield IRM unmixing isolates physically realistic EMs. Unmixing nonlinear Preisach maps elucidates these EMs in terms of domain states and their constituent magnetic phases.

Correlation between the structural phase transition and magnetic properties of sol-gel synthesized nanoparticles

The La2CoFeO6 (LCFO) nanoparticles were synthesized using the sol-gel method and calcined at 600 , 800 , and 1000 . The X-ray diffraction data confirm the successful formation of LCFO nanoparticles. The crystallite size was observed to increase from ∼13 nm to ∼26 nm as the calcination temperature rose. Detailed Rietveld analysis revealed the coexistence of both orthorhombic (Pnma: S.G. 62) and rhombohedral ( : S.G. 167) phases in the LCFO samples. A two-phase Rietveld refinement demonstrated a structural phase transition (from Pnma to ) as the calcination temperature increased. FESEM micrographs exhibited a granular morphology for the LCFO nanoparticles, and the grain size was observed to increase with the elevated calcination temperature. Magnetization curves illustrated an increase in magnetization with a decrease in crystallite size or a reduction in calcination temperature for LCFO nanoparticles. At higher calcination temperatures, the rhombohedral phase displayed significant antisite disorder, resulting in the disruption of long-range ferromagnetic ordering in the material and a subsequent decrease in maximum magnetization.

Magnetic characterisation of ferromagnetic material

In magnetic and electromagnetic non-destructive testing, the physical properties of the material are often not well known or completely unknown. The design of the non-destructive testing systems that provide the magnetisation is often oversized in order to get enough magnetic saturation (e.g. in magnetic flux leakage method or in magnetoscopy method). An improvement of the device performances, expressed usually by the signal to noise ratio, can be obtained only when the designer of the device well knows the material characteristic in terms of magnetic curve, the curve that links the magnetic field strengths to the magnetic flux density. A good device must be able to saturate the material sample under test but not to overcame determinate values. In fact, when the magnetisation is low, the leakage of the flux is negligible, while when the magnetisation is too strong the material tends to be like air and the leakage flux is negligible too. The experimental characterisation is derived from the technique adopted for the testing of soft magnetic material adopted in electrical machines or electromechanical actuators. In the present paper will be presented some material characterisation useful for the non-destructive testing of railway track, metallic ropes or reinforcement iron.

Determination of phase transformation kinetics under magnetic fields: Modeling based on magnetization and application in a Fe-1 wt.%Cu alloy

A phase transformation model based on magnetization is proposed in this paper, which accurately tracks the change in the phase transformation volume fraction with time/temperature f-T/t by analyzing phase transformation magnetization curves under a magnetic field. This allows for the determination of kinetic parameters related to the nucleation and growth processes such as the phase transformation rate df/dt-T/t and Avrami exponent n, enabling quantitative analysis of phase transformation kinetics under magnetic field effects. Additionally, the phase transformation magnetization under a magnetic field can be accurately fitted by combining the volume fraction calculation model with the Johnson–Mehl–Avrami equation, thus also obtaining the kinetics parameters. The aforementioned two models are applied to study the isothermal and isokinetic transformations of austenite (γ) to ferrite (α) in Fe-1 wt. %Cu alloys, demonstrating the effects of external conditions through variations in kinetic parameters.

Robust Algorithms for the Analysis of Fast-Field-Cycling Nuclear Magnetic Resonance Dispersion Curves

Fast-Field-Cycling (FFC) Nuclear Magnetic Resonance (NMR) relaxometry is a powerful, non-destructive magnetic resonance technique that enables, among other things, the investigation of slow molecular dynamics at low magnetic field intensities. FFC-NMR relaxometry measurements provide insight into molecular motion across various timescales within a single experiment. This study focuses on a model-free approach, representing the NMRD profile R1 as a linear combination of Lorentzian functions, thereby addressing the challenges of fitting data within an ill-conditioned linear least-squares framework. Tackling this problem, we present a comprehensive review and experimental validation of three regularization approaches to implement the model-free approach to analyzing NMRD profiles. These include (1) MF-UPen, utilizing locally adapted L2 regularization; (2) MF-L1, based on L1 penalties; and (3) a hybrid approach combining locally adapted L2 and global L1 penalties. Each method’s regularization parameters are determined automatically according to the Balancing and Uniform Penalty principles. Our contributions include the implementation and experimental validation of the MF-UPen and MF-MUPen algorithms, and the development of a “dispersion analysis” technique to assess the existence range of the estimated parameters. The objective of this work is to delineate the variance in fit quality and correlation time distribution yielded by each algorithm, thus broadening the set of software tools for the analysis of sample structures in FFC-NMR studies. The findings underline the efficacy and applicability of these algorithms in the analysis of NMRD profiles from samples representing different potential scenarios.

Optimizing the Sintering Conditions of (Fe,Co)1.95(P,Si) Compounds for Permanent Magnet Applications.

(Fe,Co)2(P,Si) quaternary compounds combine large uniaxial magnetocrystalline anisotropy, significant saturation magnetization and tunable Curie temperature, making them attractive for permanent magnet applications. Single crystals or conventionally prepared bulk polycrystalline (Fe,Co)2(P,Si) samples do not, however, show a significant coercivity. Here, after a ball-milling stage of elemental precursors, we optimize the sintering temperature and duration during the solid-state synthesis of bulk Fe1.85Co0.1P0.8Si0.2 compounds so as to obtain coercivity in bulk samples. We pay special attention to shortening the heat treatment in order to limit grain growth. Powder X-ray diffraction experiments demonstrate that a sintering of a few minutes is sufficient to form the desired Fe2P-type hexagonal structure with limited secondary-phase content (~5 wt.%). Coercivity is achieved in bulk Fe1.85Co0.1P0.8Si0.2 quaternary compounds by shortening the heat treatment. Surprisingly, the largest coercivities are observed in the samples presenting large amounts of secondary-phase content (>5 wt.%). In addition to the shape of the virgin magnetization curve, this may indicate a dominant wall-pining coercivity mechanism. Despite a tenfold improvement of the coercive fields for bulk samples, the achieved performances remain modest (HC ≈ 0.6 kOe at room temperature). These results nonetheless establish a benchmark for future developments of (Fe,Co)2(P,Si) compounds as permanent magnets.

Antioxidant activity and cytotoxicity of greigite nanoparticles synthesized by hydrothermal technique.

The effects of 180, 210, and 230°C reaction temperatures on the structural and magnetic properties of synthesized iron sulfide nanoparticles were studied. The Rietveld refinement analysis result of the X-ray diffraction data indicated that greigite was the dominant phase in all samples. The sample was prepared at 210°C for 18h and had a greater wt% ratio of the greigite phase. The crystallite and particle sizes increased with increasing reaction temperatures. Scanning electron microscope images confirmed the presence of aggregation of synthesized rod-shaped nanoparticles. The magnetic hysteresis curves of all samples showed ferromagnetic behavior at room temperature. The magnetic saturation of three samples increases with increased reaction temperature, but the coercive force has the opposite behavior. Antioxidant activity and cytotoxicity of the sample synthesized at 210°C were investigated. This sample killed cancer cells at relatively moderate and high concentrations with high viability of normal cells, demonstrating the sample's suitability for use in killing cancer cells while avoiding normal cells.