Saturation Magnetization Measurements Research Articles

Observation of Hydrostatic‐Pressure‐Modulated Giant Caloric Effect and Electronic Topological Transition

AbstractPhase transition is a fundamental phenomenon in condensed matter physics, in which states of matter transform to each other with various critical behaviors under different conditions. The magnetic martensitic transformation features significant multi‐caloric effects that benefit the solid‐state cooling or heat pumping. Meanwhile, the electronic topological transition (ETT) driven by pressure has been rarely reported in martensitic systems. Here, the modulation effects of hydrostatic pressure on phase transitions in a magnetic martensitic alloy are reported. Owing to the huge volume expansion during the transition, the martensitic transition temperature is driven from 339 to 273 K by pressure within 1 GPa, resulting in highly tunable giant baro‐ and magneto‐caloric effects (BCE and MCE) in a wide working temperature range. Interestingly, an ETT is further induced by pressure in the martensite phase, with a sudden drop of the measured saturation magnetization around 0.6 GPa. First‐principles calculations reveal a sharp change in the density of states (DOS) due to the orbit shift around the Fermi level at the same pressure and reproduce the experimental observation of magnetization. Besides, the ETT is accompanied by remarkable changes in the lattice parameters and the unit‐cell orthorhombicity. The study provides insight into pressure‐modulated exotic phase‐transition phenomena in magnetic martensitic systems.

Magnetic microscopy using Hall effect sensors biased with pulsed currents

In this article, we describe the programs for instrument control, data acquisition, and analysis developed to adapt a Scanning Magnetic Microscope for the Delta Mode technique. This adaptation led to the elimination of thermoelectric effects and introduced a novel approach to data acquisition during mapping by employing a pulsed current bias for Hall effect sensors. When comparing the adapted system to a commercial magnetometer, we observed average errors of 1.2 % in the measurement of saturation magnetization, utilizing a nickel sphere with 99 % purity. Furthermore, through a sample holder with three cylindrical cavities, we investigated a methodology to characterize samples at the microgram level with different magnetizations, simulating the interaction between the induced magnetic fields. The theoretical and experimental results emphasized the geometric possibilities in the design of a sample holder to estimate magnetizations of various samples simultaneously, demonstrating the effectiveness of the Scanning Magnetic Microscope with Delta Mode.

Study of CoCe0.05Fe1.95O4-polypyrrole composite for efficient electromagnetic interference shielding

The synthesis of nanocomposites with magnetic and microwave absorbing properties was achieved via sol-gel process merge with the self-combustion methodology. The X-ray diffraction results showed that nanocomposites consisted of a single spinel phase and no impurities were detected. The hysteresis loop showed the nanocomposites' ferromagnetic character. Measurements of saturation magnetization, alternating current susceptibility, cation distribution, and Curie temperature were taken to evaluate the magnetic properties. The permittivity (ε′, ε″) varied as a function of frequency in accordance with Maxwell-Wagner type interfacial polarization. The actual and fictitious components of microwave permeability showed a maximum at lower frequencies and decreased as frequency increased. Due to its superparamagnetic behavior, the composite has potential applications in shielding technologies.

Magnetic properties of (Ni0.81Fe0.19/SiO2)n multilayers for high frequency on-wafer inductor applications

We investigated the magnetic properties of multilayer stacks of Ni81Fe19 thin films separated with SiO2 intended for use in inductors operating at sub-GHz frequencies. We measured saturation magnetization, anisotropy field, coercivity, and complex permeability of sputtered multilayer structures consisting of thin film stacks of 5, 10, 15, 20, and 25 layers, ranging from 160 to 1455 nm in total magnetic material thickness. Our analysis indicates that multilayer stacks composed of repeated layers thinner than 115 nm generally maintained the desired magnetic properties found in individual thin films, such as high permeability, low anisotropy, and low coercive field. Moreover, the multilayer stacks did not exhibit unwanted characteristics such as stripe domain formation and decreased value of real permeability, which commonly occurred in single thicker films. These properties make them suitable for on-wafer inductor applications.

Preparation of Functionalized Magnetic Polystyrene Microspheres and Their Application in Food Safety Detection.

Based on the specific binding of sulfonic acid groups to melamine, β-agonists and other compounds, Fe3O4 nano-magnetic beads were coated with polystyrene using an improved micro-suspension emulsion polymerization method, thus forming core-shell magnetic polystyrene microspheres (Fe3O4@PS) with Fe3O4 as the core and polystyrene as the shell. These functionalized microspheres, which can be used as magnetic solid-phase extraction (MSPE) adsorbent, were prepared after further sulfonation. These microspheres were characterized by Fourier transform infrared spectroscopy (FTIR), scanning electron microscopy (SEM), transmission electron microscopy (TEM), particle size analysis and saturation magnetization measurement. The results showed that these sulfonated magnetic polystyrene microspheres had favorable sphericity. The particle size of these microspheres ranged from 1 μm to 10 μm. Additionally, these microspheres had good dispersion and magnetic responses in both inorganic and organic solvents. Moreover, these functionalized magnetic polystyrene microspheres were tested and evaluated by high performance liquid chromatography tandem mass spectrometry (HPLC-MS/MS). The results indicated that these sulfonated magnetic polystyrene microspheres (Fe3O4@SPS) could effectively adsorb such illegal additives as β-agonists and melamine in the food matrix.

Room temperature ferromagnetism in oxygen-deficient gallium oxide films with cubic spinel structure

Oxygen-defective gallium oxide (Ga2O3-x with 0.4 < x < 0.7) thin films with cubic spinel structure were deposited on c-cut epi-polished sapphire wafers using thermal evaporation technique by keeping specific values of oxygen partial pressure in the evaporation chamber. The preparation method and post-treatment conditions induced distinct oxygen stoichiometries in the films which exhibit a ferromagnetic-like behavior at room temperature. Despite the measured saturation magnetization values do not exhibit a straightforward correlation to the oxygen stoichiometry of the films, the presence of oxygen vacancies and defects is presumably the origin of the unconventional magnetic behavior. Strong magnetic irreversibility exhibit by the magnetization measurements performed using field-cooling and zero-field-cooling protocols indicate the presence of disordered magnetic moment distributions which are likely non-collinear. Theoretical and experimental results available in the literature corroborate with the assumptions that oxygen vacancies and defects appear as the main reason for room-temperature ferromagnetism. All films exhibit soft magnetic behavior at room temperature, exhibiting remanent magnetizations between 7% and 20% of the saturation magnetization which saturated magnetic moments is estimated as 0.43 and 1.24 Bohr magneton per oxygen vacancy. The present results extend the functionalities of this interesting material, which is already investigated for applications in several technological areas, for possible uses in the areas of spintronics and emerging areas of the optospintronics.

Studies of the correlations between physical properties and complex permeability of NiFe thin films

We investigated the physical properties of Ni81Fe19 thin films intended for use in inductors operating at high frequencies. With a variety of characterization techniques, we measured saturation magnetization, anisotropy field, resistivity, and complex permeability of sputtered films with thicknesses in the range of 16–910 nm. We correlated the physical properties of the films with their complex permeability. Our analysis indicates that films under 100 nm have the characteristics most suitable for use in inductor structures. Such films would exhibit high permeability, allow inductors to operate at high frequencies and, at the same time, minimize eddy current losses.

Modeling of the Kinetics of Strain‐Induced Martensite Transformation and the Transformation‐Induced Plasticity Effect in a Lean‐Alloyed Metastable Austenitic Stainless Steel

This article investigates the influence of temperature and strain on second‐phase transformation strengthening and the resulting mechanical properties in a lean AISI 301LN austenitic stainless steel within a temperature range of −60 to 180 °C. The volume fraction of martensite evolved is determined using nondestructive magnetic Ferritescope measurements that are adjusted by using a calibration factor of 1.7, which is established using the saturation magnetization measurements, X‐ray, and neutron diffraction measurements. The kinetics of strain‐induced martensite transformation (SIMT) as a function of strain and temperature is accurately described by a set of modified constitutive Boltzmann sigmoidal equations at temperatures below 75 °C. For this steel, the Md (30/50) temperature is determined as 61 °C. The absolute Md temperature is established as ≈109 °C, and no athermal transformation to martensite is observed upon cooling to −270 °C using cryogenic neutron diffraction facilities. Extended JMAK analysis of the transformation is used to shed light on the mechanism of martensitic transformation. It is found that the transformation‐induced plasticity (TRIP) effect due to SIMT is at a maximum at 75 °C, which is the maximum elongation temperature (MET) and calculations are performed regarding alloy development which will reduce the MET to room temperature.

Microstructure, magnetic, and dielectric interplay in NiCuZn ferrite with rare earth doping for magneto-dielectric applications

The homogeneous conglomerate of ferrite oxide samples with increasing concentration of Neodymium and Lanthanum in the steps 0.02 with the chemical formula Ni0.6Cu0.2Zn0.2Fe2-x(Nd0.5La0.5)xO4 (0 ≤ x ≤ 0.10) were achieved by novel citric acid-metal nitrate sol–gel auto-ignition method. The nano-regime crystallites products were achieved by using Ni, Cu, Zn, La, Nd and Fe nitrates and keeping the metal nitrate to citrate ratio 1:1. The products of ensured recipe in the form of chemical formula resulted in precursor powders were calcined for removal of desiccated impurities. The ready blends were subjected to an exhaustive examination with distinctive characterizations. The completion of the reaction and phase formation temperature was confirmed by thermal analysis and structural confirmations were received by X-ray diffraction (XRD), Scanning electron microscopy (SEM), and Fourier transform infrared (FTIR) spectra. The analytics regarding the local symmetry in crystalline solids and understandings about the ordering phenomenon were discussed with the support of FTIR spectra. The diffractograms contributed to the corroboration that the powders obtained were bearing single phase and spinel structure. Evaluation of TEM and DLS confirms fine particle nature of the particles. SEM analysis and EDAX indicated that the samples were having dense, homogeneous and expected stoichiometric cation ratios. The neodymium and lanthanum content influenced the measured saturation magnetization negatively and coercivity positively. The heightened values in electrical conductivity, high ε′ and low dielectric losses in combination with high saturation magnetization, low coercivity, observed in the present samples make them prospect candidate for microwave and electromagnetic shielding applications.

Thermal decomposition characteristics of retained austenite and its influence on impact toughness of B-containing 9Cr1Mo1Co(FB2) steel during the two-step tempering

The decomposition kinetics of retained austensite (RA) and the effect of its decomposition on the impact toughness of FB2 steel during the two-step tempering were studied by employing differential scanning calorimetry (DSC), magnetic saturation measurement (MSM) and transmission electron microscopy (TEM). Furnace-cooling from 1100 °C produces 9.7vol.% filmy RA due to the contributions to Ms from the C enrichment (MS(Che) = 102 °C) and the high internal stress (ΔMS(stress) = -93.3 °C). With the increase of the first step tempering temperature from 570 °C to 630 °C for 1–10 h, RA involves into the different decomposition characteristics, forming θ phase, M3C particles, filmy M3C and M7C3, and also leading to the volume fraction of the carbon-depleted RA transformed into martensite fγRA→M decrease from 87.6% to 0.0% during the subsequent cooling process. During the second step tempering at 670 °C, these θ and M3C particles evolve into spherical M23C6, while film-like M3C and M7C3 evolve into filmy M23(C,B)6. Deteriorated by the filmy M23(C,B)6, the impact toughness increase from 72 J/cm2 to 118 J/cm2 with the increase of fγRA→M from 0% to 87.6%. While for the samples with fγRA→M=0, enhancing the second step tempering temperature to 690 °C for 10 h can further promote the spheroidization of filmy M23(C,B)6 and reduce hardness, resulting in the enhancement of impact toughness from 72 J/cm2 to 112 J/cm2. In summary, a two-step tempering process (570 °C for 1–5 h plus 670–690 °C for 10 h) for RA-containing FB2 steel is suggested to obtain excellent impact toughness and high hardness.

Electron-beam evaporated bismuth ferrite (BiFeO3) thin films and characterization

The BiFeO3 (BFO) thin films made by the electron beam evaporator are systematically investigated. As the most difficult part of this work, the preparation process is repeated until the optimal deposition power and elemental composition of BFO are obtained. With the help of X-ray diffraction and Raman spectroscopy, we specify precisely that the sample annealed at the temperature of 650 °C is the purest BFO phase with rhombohedral R3c structure. The Scanning Electron Microscopy images provide the surface morphology and cross-sectional thickness of each sample for the further performance analysis. With the aim of understanding the changes in the chemical bond structure of BFO samples at the different annealing temperatures, we applied X-ray photoelectron spectroscopy and the result indicates that the absorption of oxygen is increasing with the raising of the annealing temperature. Finally, we measured the magnetic property and resistivity of BFO samples to explore their applications. The saturation magnetization measurement shows the correlation between the magnetization of BFO and microstructures such as phase structure, grain size. Meanwhile, the electronic resistivity explains the close relationship between the resistivity and surface morphology.

Effect of Annealing on the Characteristics of CoFeBY Thin Films

In this study, the addition of Y to CoFeB alloy can refine the grain size to study the magnetic, adhesion and optical properties of as-deposited and annealed CoFeB alloy. XRD analysis shows that CoFeB(110) has a BCC CoFeB (110) nanocrystalline structure with a thickness of 10–50 nm under four heat-treatment conditions, and a CoFeB(110) peak at 44° (2θ). The measurements of saturation magnetization (MS) and low frequency alternate-current magnetic susceptibility (χac) revealed a thickness effect owed to exchange coupling. The maximum MS of the 300 °C annealed CoFeBY film with a thickness of 50 nm was 925 emu/cm3 (9.25 × 105 A/m). The maximum χac value of the 300 °C annealed CoFeBY nanofilms with a thickness of 50 nm was 0.165 at 50 Hz. After annealing at 300 °C, CoFeBY nanofilms exhibited the highest surface energy of 31.07 mJ/mm2, where the thickness of the nanofilms was 40 nm. Compared with the as-deposited CoFeBY nanofilms, due to the smaller average grain size after annealing, the transmittance of the annealed nanofilms increased. Importantly, when a CoFeB seed or buffer layer was replaced by a CoFeBY nanofilm, the thermal stability of the CoFeBY nanofilms was improved, promoting themselves on the practical MTJ applications.

Low Cost Corn Cobs-Based Magnetic Nanocomposite for Massive Adsorption of Cu(II) Ions from Aqueous Media

ABSTRACT A low-cost corn cobs-based magnetic nanocomposite was prepared, characterised and investigated for the adsorption of Cu(II) ions from aqueous media. Several characterisation studies were executed to confirm the formation of the adsorbent. Furthermore, the magnetic property of the prepared adsorbent was confirmed by saturation magnetisation measurements. An adsorption scenario was proposed and executed to address the optimal adsorption conditions for the removal of Cu(II) ions by the prepared adsorbent. The optimal adsorption conditions were found to be pH 6.0, 10.0 min contact time and 0.5 g/L adsorbent dose. The adsorption process was rapid with a reasonable adsorption capacity. The adsorption process was found to follow the Langmuir isotherm model with pseudo-second-order kinetic. Moreover, the process is spontaneous and exothermic. Taking into account the pros of low cost, easy separation, environmental friendliness and appropriate adsorption capacity, the prepared corn cobs-based magnetic nanocomposite is an outstanding adsorbent for the removal of Cu(II) ions from aqueous media.

Magnetic properties of γ-Fe2O3 nanoparticles in a porous SiO2 shell for drug delivery

A method is presented for synthesizing core–shell nanoparticles with a magnetic core and a porous shell suitable for drug delivery and other medical applications. The core contains multiple γ-Fe2O3 nanoparticles (∼15 nm) enclosed in a SiO2 (∼100–200 nm) matrix using either methyl (denoted TMOS-γ-Fe2O3) or ethyl (TEOS-γ-Fe2O3) template groups. Low-temperature Mössbauer spectroscopy showed that the magnetic nanoparticles have the maghemite structure, γ-Fe2O3, with all the vacancies in the octahedral sites. Saturation magnetization measurements revealed that the density of γ-Fe2O3 was greater in the TMOS-γ-Fe2O3 nanoparticles than TEOS-γ-Fe2O3 nanoparticles, presumably because of the smaller methyl group. Magnetization measurements showed that the blocking temperature is around room temperature for the TMOS-γ-Fe2O3 and around 250 K for the TEOS-γ-Fe2O3. Three dimensional topography analysis shows clearly that the magnetic nanoparticles are not only at the surface but have penetrated deep in the silica to form the core–shell structure.

An efficient and simple procedure to prepare chemically stable and partially carbon-cleaned magnetite from solid-state synthesis for clinical practices in medical oncology

As far as medical applications for clinical diagnosis and therapy in oncology are concerned, the use of stables magnetic nanoparticles relies on the magnetocaloric response of their ferrofluid suspensions to an applied alternating current magnetic field. To assure their effectiveness as an advanced material for such a medical technology, some critical properties, as any tendency of the nanoparticles to self-agglomerate and of the magnetic core component to somehow change their chemical nature, must be rigorously inhibited. A sample of chemically stable nanoparticles of magnetite ( Fe23+Fe2+O42-) was synthesized through the method consisting of burning a synthetic commercial maghemite (γFe23+O32-) with admixed sucrose, to partially reduce Fe3+ → Fe2+. The residual carbon, formed on burning the sucrose, tends to coat the nanoparticles and acts as a protective layer hindering the freshly synthesized hot magnetite from being promptly re-oxidized, on cooling the sample in the open-air atmosphere. As a drawback, this carbon layer tends to be a thermal insulator and must be removed, in order to make the magnetite nanoparticles able to be used as a magnetocaloric material and dissipate heat. A chemically gentle removal of the residual carbon was assayed by treating the sample with H2O2 under stirring or sonication either for 30 min or 60 min. The intrinsic atomic and crystalline structures and other essential properties of this core-shell system were assessed by gas adsorption analysis (BET), powder X-ray diffraction, Fourier-transform infrared spectrometry, Mössbauer spectroscopy and transmission electron microscopy. Theoretical analyses based on the density functional theory (DFT) were used to interpret the harmonic infrared spectra for the produced magnetite. The efficiency in removing the residual carbon layer formed on the magnetite grain surface was checked by saturation magnetization measurements and CHN elemental analysis. The heat releasing ability of the prepared magnetic sample was evaluated under an AC-induced magnetic field. These results evidenced that the treatment with H2O2 was efficient enough to remove, even though not completely, most of the residual carbon layer, which made the saturation magnetization and the heat released by the treated samples significantly greater than that of the untreated carbon-coated grains. The resulting nano-magnetite was found to be a sufficiently clean material for being used for hyperthermia-based procedures, particularly for medical diagnosis and therapy, in oncology.

The Effect of Severe Plastic Deformation on the Corrosion Resistance of AISI Type 304L Stainless Steel

The AISI type 304L stainless steel (SS) was solution annealed at 1050 °C and cryo-rolled at liquid nitrogen (L-N2) temperature (77 K) under severe plastic deformation (SPD). The thickness reduction through cryo-rolling plastic deformation was carried out up to 90% (designated as CR-90) of initial thickness. The cryo-rolling during rolling at liquid N2 temperature (77 K), resulted in transformation induced plastic deformation of the austenite γ-phase into α’- martensite phase. The phase transformation was characterized by x-ray diffraction (XRD) and saturation magnetization (Ms) measurement. The microstructure was measured by using optical microscopy (OM), scanning electron microscopy (SEM) and transmission electron microscopy (TEM). The XRD peak positions confirmed the martensite (α’) phase formation. Saturation magnetization (Ms) value of the cryo-rolled specimens shows increasing linearity with cryo-rolling, and transformed to bct martensite (α’). The measured corrosion rate of the cryo-rolled specimens as per ASTM A-262 practice-C test (Huey test) ranges from 6.6 mpy or 0.167 mm/yr (CR 0) to 12.9 mpy or 0.328 mm/yr (CR 90), indicating the effects of severe deformation of strain-induced martensite with the cryo-rolling. Further, the role of severe deformation of strain-induced martensite with the cryo-rolling on AISI type 304L SS and also influence on the corrosion resistance are investigated in detail. The deformation microstructure roles, i.e., the phases and volume percentage induced by the different percentage of the cryo-rolling that influences the corrosion resistance properties and corresponding corrosion resistance in nitric acid have been investigated.

High photocatalytic activity of magnetically separable ZnO and Ag/ZnO supported on Mg-ferrite nanoparticles

Facile precipitation–deposition method has been used to prepare magnetically recoverable MgFe2O4/ZnO and MgFe2O4/ZnO/Ag nanocomposites. The valuation of photocatalytic activity of prepared powders was carried out using Congo red (CR) as a model of chemical pollutants, under visible light irradiation. The XRD, FE-SEM, TEM, DRS and VSM were applied to characterize the prepared nanocomposites. Structural, compositional and morphological analysis showed the successful formation of the nanocomposites with spherical shapes. The particle sizes of all the compositions were in the range of ∼39–69 nm. The MgFe2O4/ZnO and MgFe2O4/ZnO/Ag nano-photocatalyst showed higher degradation efficiency than the pure ZnO and Mg-ferrite. The enhanced photocatalytic activity of the nanocomposites is attributed to the development of a suitable internal structure between ZnO and MgFe2O4. The measured saturation magnetization of the nanocomposites with and without doping of Ag were 8.09 and 7.71 emu/g, respectively, indicating that these photocatalysts could be quickly separated from the reaction solution by an external magnetic field.

Electrodynamic theory of ferromagnetic resonance and its applications in precise measurements of ferromagnetic linewidth, permeability tensor and saturation magnetization

This review paper describes the state of the art in measurements of ferromagnetic linewidth, permeability tensor and saturation magnetization employing electrodynamic theory of ferromagnetic resonance. It is shown that the electrodynamic theory allows significant improvements of measurement accuracy of these parameters with respect to the commonly used perturbation and magnetostatics theories. Contrary to the perturbation method the electrodynamic theory is not limited to small samples. It allows determination of the resonance frequencies and Q-factors for arbitrary size spherical and cylindrical gyromagnetic samples in suitably chosen metal enclosures. Results obtained with the electrodynamic theory for very small samples are identical to those obtained with perturbation and magnetostatics theories. Results of measurements of the ferromagnetic linewidth, permeability tensor and saturation magnetization at microwave frequencies are presented.

Mutual Verification of Phase Fraction Analysis Techniques for Steels Comprising Deformation Induced Martensite Phases: Neutron-Diffraction-Based Rietveld Texture Analysis and Saturation Magnetization Measurement

Mutual Verification of Phase Fraction Analysis Techniques for Steels Comprising Deformation Induced Martensite Phases: Neutron-Diffraction-Based Rietveld Texture Analysis and Saturation Magnetization Measurement

Effect of Manganese on the Structure-Properties Relationship of Cold Rolled AHSS Treated by a Quenching and Partitioning Process

The present work focuses on the investigation of both microstructure and resulting mechanical properties of different lean medium Mn Quenching and Partitioning (Q&amp;P) steels with 0.2 wt.% C, 1.5 wt.% Si, and 3–4 wt.% Mn. By means of dilatometry, a significant influence of the Mn-content on their transformation behavior was observed. Light optical and scanning electron microscopy (LOM, SEM) was used to characterize the microstructure consisting of tempered martensite (α’’), retained austenite (RA), partially bainitic ferrite (αB), and final martensite (α’final) formed during final cooling to room temperature (RT). Using the saturation magnetization measurements (SMM), a beneficial impact of the increasing Mn-content on the volume fraction of RA could be found. This remarkably determined the mechanical properties of the investigated steels, since the larger amount of RA with its lower chemical stabilization against the strain-induced martensite transformation (SIMT) highly influenced their overall stress-strain behavior. With increasing Mn-content the ultimate tensile strength (UTS) rose without considerable deterioration in total elongation (TE), leading to an enhanced combination of strength and ductility with UTS × TE exceeding 22,500 MPa%. However, for the steel grades containing an elevated Mn-content, a narrower process window was observed due to the tendency to form α’final.