Magnetic Hysteresis Curves Research Articles

Cation distribution and microwave absorptive behavior of gadolinium substituted cobalt ferrite ceramics

In the first step, gadolinium substituted cobalt ferrite nanoparticles with composition of CoFe2-xGdxO4 (x = 0–0.05 in a step of 0.01) were synthesized by a hydrothermal technique and without subsequent annealing. X-ray diffraction and field-emission scanning electron microscopy evaluations exhibited that single phase spinel ferrites with narrow size distribution were achieved. The EDS analysis confirmed that the applied process for fabrication of CoFe2-xGdxO4 nanoparticles is a proper process for the synthesis of spinel cobalt ferrites with homogeneity in composition. Mössbauer spectroscopy was utilized to distinguish the site preference of constitutive elements. A well-resolved doublets pattern of ferrite nanoparticles is mainly attributed to the superparamagnetic behavior. The results of magnetic hysteresis revealed that the gadolinium substituted cobalt ferrite nanoparticles exhibit superparamagnetic trend at a room temperature. The zero field cooled magnetization curves of gadolinium substituted cobalt ferrite nanoparticles showed that with an increase in gadolinium content, the blocking temperature increases. Fitting the experimental data of susceptibility with the Neél-Brown model expresses that there are powerful interactions between nanoparticles of gadolinium substituted cobalt ferrite and the Neél-Brown model was not operate for such ferrites. In the second step, the gadolinium substituted cobalt ferrite nanoparticles were annealed and the structural characteristics, magnetic properties and microwave absorptive behavior were evaluated. The Mössbauer spectras show a well-resolved six-line pattern of ferrite nanoparticles which is mostly imputed to the ferrimagnetic treatment. The magnetic hysteresis loops at a room temperature confirmed that the coercive field increased from 802 Oe for x = 0 to 965 Oe for x = 0.02 and then at higher contents, decreased. The magnetic hysteresis curves of CoFe1.98Gd0.02O4 for fields applied parallel and perpendicular to the sample axis, expresses high value of magnetocrystalline anisotropy field of 13 kOe which exhibits that the resonance frequency can be shifted to higher frequency. Consequently the microwave absorber can be covered a wide-band of electromagnetic waves in the X-band.

Magnetic anisotropy properties of Co1.2Fe1.8–xMnxO4 (0.0 ⩽ x ⩽ 0.3) nanopowders: theory and experiment

We perform a theoretical and experimental investigation of the magnetic properties of a series of Mn-substituted non-stoichiometric cobalt ferrite nanopowders. We propose a theoretical approach based on the Stoner–Wohlfarth model of coherent rotation of single-domains, considering mean-field interactions between the nanograins. In particular, we provide a detailed description of the magnetic anisotropy behavior, considering tetragonal distortions of the cubic spinel structure of the system. Our model shows that the effects of the tetragonal distortion of the cubic structure may be modeled by a superposition of uniaxial and cubic magnetocrystalline anisotropies. We obtain the uniaxial and cubic anisotropy constants and the mean-field parameters by fitting numerically the experimental magnetic hysteresis curves. Thus, the agreement between theory and experiment provides support to confirm the validity of our theoretical approach, in addition our results corroborate experimental works found in the literature reporting that cobalt ferrites present tetragonal distortion of the well-known cubic spinel structure.

Mössbauer studies of Ba3Zn2Fe24O41 Z-type hexaferrite

A Ba3Zn2Fe24O41 polycrystalline sample of Zn doped Z-type hexaferrite was prepared by using solid-state reaction method. From the XRD pattern, analyzed by using the Rietveld refinement method at 295 K, the samples were found to be single-phased, and the crystal structure of sample was determined to be hexagonal with space group P63/mmc. From the magnetic hysteresis curves at 295 K, the saturation magnetization (Ms) and coercivity (Hc) of sample were Ms = 58.70 emu/g and Hc = 69.58 Oe, respectively, and the samples showed ferrimagnetic behavior. From the temperature dependence of the zero-field-cooled magnetization curves under a magnetic field of 100 Oe at temperatures between 300 and 800 K, the spin transition from planar order to uniaxial order was observed around 400 K, and the Curie temperature (TC) was found to be 643 K. Mossbauer spectra of sample were also taken and analyzed at various temperatures ranging from 4.2 to 295 K. The relative areas obtained from the Mossbauer spectra suggest that the Zn ions preferentially occupy the tetrahedral sublattices.

Wasp-waisted behavior in magnetic hysteresis curves of CoFe2O4 nanopowder at a low temperature: experimental evidence and theoretical approach

We theoretically and experimentally investigated wasp-waisted magnetic hysteresis curves at a low temperature for CoFe2O4 nanopowders.

Structural, morphological and magnetic properties of Eu-doped CoFe2O4 nano-ferrites

Europium (Eu) doped spinel cobalt ferrites having composition CoEuxFe2−xO4 where x=0.00, 0.03, 0.06, 0.09, 0.12 were fabricated by co-precipitation route. In order to observe the phase development of the ferrite samples, thermo-gravimetric analysis was carried out. The synthesized samples were subjected to X-ray diffraction analysis for structural investigation. All the samples were found to constitute face centered cubic (FCC) spinel structure belonging to Fd3m space group. Scanning electron microscopy revealed the formation of nanocrystalline grains with spherical shape. Energy dispersive X-ray spectra confirmed the presence of Co, Eu, Fe and O elements with no existence of any impurity. The magnetic hysteresis curves measured at room temperature exhibited ferrimagnetic behavior with maximum saturation magnetization (Ms) of 65emu/g and coercivity (Hc) of 966Oe. The origin of ferrimagnetism in Eu doped cobalt ferrites was discussed in detail with reverence to the allocation of Co2+ and Fe3+ ions within the spinel lattice. The overall coercivity was increased (944–966Oe) and magnetization was decreased (65–46emu/g) with the substitution of Eu3+. The enhancement of former is ascribed to the transition from multi domain to single domain state and reduction in lateral is attributed to the incorporation of nonmagnetic Eu ions for Fe, resulting in weak superexchange interactions.

Temperature Dependence of the Magnetic Hysteresis Curves in Magnetic Multilayers

Temperature Dependence of the Magnetic Hysteresis Curves in Magnetic Multilayers

Aluminum Nano-polycrystalline Substance with Ferromagnetics and Application to High-Frequency Core Inductor

It has showed in experiments that aluminum nano-polycrystalline substances are ferromagnetic. A magnetic hysteresis curve measured by SQUID suggested the ferromagnetism. Al bulk is normally thought to be non-magnetic body. Authors also fabricated core inductors using Al nano-polycrystalline substances and measured the inductances of cored inductors with frequency dependence. Al nano-polycrystalline substance was fabricated by sintering Al nanopaste with Al nanoparticles. Al nanoparticles were prepared by using laser ablation in liquid. The structures and components of the sintered Al nano-polycrystalline substances were analyzed by SEM and EDX. It has been shown that inductor using Al nano-polycrystalline substance with low volume resistivity, which is the same order of metal, works at low frequencies below 500 Hz, while inductor using substance with high volume resistivity works at high frequency of 5 MHz. Our analysis of Al nano-polycrystalline substance with high volume resistivity revealed relative permittivity of 7 at frequency of 1 MHz. It has been expected that these inductors to work at frequency of a few GHz because the magnetic resonance frequency of the Al nano-polycrystalline substances were evaluated to be 5.6 GHz and the high volume resistivity results in suppressing the eddy currents.

Influence of the applied elastic tensile and compressive stress on the hysteresis curves of Fe-3%Si non-oriented steel

The influence of applied elastic tensile stress up to 120MPa and compressive stress up to 35MPa on the magnetic hysteresis curves of non-oriented Fe-3%Si steel is studied. In two tensile stress ranges the hysteresis loop changed monotonously – low stress below 10MPa facilitated the magnetization process, while above 15MPa tension deteriorated magnetic properties. This difference in behavior corresponds to two different mechanisms – 1) favoring by tensile stress magnetic easy axes closest to the filed direction and 2) appearance of large demagnetizing fields at grain boundaries and the sample surface. Compression continuously deteriorated magnetic properties and made the hysteresis loop constricted above a few MPa. The effective field as a product of two functions – of the magnetization and of the stress gave excellent agreement with experimental curves for both tensile stress ranges and for compression. The sensitivity of magnetization to compression was approximately five times larger than to tension. The complex hysteresis loop behavior under tension and compression was explained on the basis of our previous results on stressed grain-oriented steel of the same composition, in which the magnetic domains were also studied.

Triangular Ising Ferromagnet with Mixed Spins (A = 1/2, B = 1/2, C = 1): Dynamic Magnetic Properties and Hysteresis Curves

The dynamic properties of the triangular Ising ferromagnet consisting of the mixed spins A = 1/2, B = 1/2, and C = 1 is studied by using the mean-field theory (MFT) as well as Glauber-type stochastic dynamics (GSD). The coupling equations to investigate dynamic behaviors of the system are calculated, and phase transitions, phase diagrams, and hysteresis curves are obtained. From these studies, first- and second-order transition lines, the dynamic phase diagrams (DPDs) in the (T,h 0) and (T,d) planes, and single hysteresis curves are presented. In the DPDs, dynamic tricritical point due to the first- and second-order phase transitions are observed. It is found that the dynamic hysteresis properties of the triangular system strongly depend on the temperature and crystal field.

Magnetic recyclable photocatalysts of Ni-Cu-Zn ferrite@SiO2@TiO2@Ag and their photocatalytic activities

Abstract Ag nanoparticles with different weight percentage loaded on Ni-Cu-Zn ferrite@SiO 2 @TiO 2 composite were successfully prepared via sol-gel method. The effect of deposited amount of Ag nanoparticles on structural, magnetic and photocatalytic properties of the composite was investigated. XPS characterization confirmed that Ag nanoparticles deposited on the surface of Ni-Cu-Zn ferrite@SiO 2 @TiO 2 composite. Particle size and shape of magnetic recyclable photocatalysts were observed using TEM, showing a core-shell structure with an average particle size of 20 nm of Ag. Based on room temperature magnetic hysteresis curves, as 0.4 wt% Ag immobilized on Ni-Cu-Zn ferrite@SiO 2 @TiO 2 composite revealed the maximum saturation magnetization of 39.9 emu/g. Photocatalytic degradation of Ni-Cu-Zn ferrite@SiO 2 @TiO 2 @Ag was carried out in methylene blue (MB) solutions illuminated under a 35-W Xe arc lamp and color temperature of 6000 K. The results revealed that 83.9% of MB was photodegraded for 0.4 wt% of Ag-loaded Ni-Cu-Zn ferrite@SiO 2 @TiO 2 . Moreover, it can be easily separated and recycled without significant loss of photocatalytic activity after being used five times. Compared to the conventional photocatalysts, the magnetic core–shell photocatalyst is suitable for large scale applications in industrial wastewater system.

Magneto-optical properties and Mössbauer Investigation of BaxSryPbzFe12O19 Hexaferrites

Ba0.3Sr0.4Pb0.3Fe12O19, Ba0.4Sr0.3Pb0.3Fe12O19 and Ba0.3Sr0.3Pb0.4Fe12O19 hexaferrites were synthesized via sol-gel auto combustion. XRD (X-ray powder diffraction) powder patterns of the products confirmed the formation of M-type hexaferrites without any secındary phase. The crystallite sizes of the products were calculated as 37–41nm by Scherrer equation. SEM (Scanning electron microscopy) analyses revelaed the hexagonal morphology and 200–400nm grain size of the prodcuts. The magnetic hysteresis (σ-H) curves exhibit the ferromagnetic features for all hexaferrites. Especially, Ba0.3Sr0.4Pb0.3Fe12O19 and Ba0.4Sr0.3Pb0.3Fe12O19 samples have suitable magnetic characteristics (saturation magnetizations as 42.58 and 38.55emu/g, coercive fields as 1950 and 2978Oe, larger squareness ratios (SQR) as 0.447 and 0.454, respectively) for high density magnetic recording applications and permanent magnet fabrication. Effective crystalline anisotropy constants (Keff) are between 3.18×105–3.54×105Erg/g. The observed 17000OeHa (anisotropy field) reveal that products are hard magnet. Tauc plots were plotted to determine the Eg (direct optical energy band gap) of the samples. The Eg values are 1.46, 1.51, 1.69eV belonging to Ba0.3Sr0.4Pb0.3Fe12O19, Ba0.4Sr0.3Pb0.3Fe12O19, and Ba0.3Sr0.3Pb0.4Fe12O19 hexaferrites respectively.

A stereographic projection based phase field model for ferromagnetics

AbstractBy using the stereographic projection to satisfy the constant magnetization magnitude, a constraint‐free phase field model is developed for ferromagnetic materials. Implemented by finite element method, the model is shown to be capable of simulating magnetic domain, vortex, and hysteresis curves. (© 2016 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Spin/orbital and magnetic quantum number selective magnetization measurements for CoFeB/MgO multilayer films

Spin selective magnetic hysteresis (SSMH) curves, orbital selective magnetic hysteresis (OSMH) curves and magnetic quantum number selective SSMH curves are obtained for CoFeB/MgO multilayer films by combining magnetic Compton profile measurements and superconducting quantum interference device (SQUID) magnetometer measurements. Although the SQUID magnetometer measurements do not show perpendicular magnetic anisotropy (PMA) in the CoFeB/MgO multilayer film, PMA behavior is observed in the OSMH and SSMH curves for the |m| = 2 magnetic quantum number states. These facts indicate that magnetization switching behavior is dominated by the orbital magnetization of the |m| = 2 magnetic quantum number states.

From an Anomalous Peak Effect to a Second Magnetization Peak in Nb-rich Nb-Ti Alloys

We investigated the evolution of the DC magnetic hysteresis curves of Nb 0.89Ti 0.11 alloys thermo-mechanically processed by intermediate heat treatments at 900 ∘C in vacuum and cold rolling (∼ 50 % thickness reduction). Starting with a rectangular piece (∼ 0.4 mm thick) cut from the as-grown alloy, after the first thermo-mechanical treatment, the specimen exhibits over a wide temperature T interval a peak effect not far from the DC irreversibility line. With a supplemental thermo-mechanical treatment, the peak effect disappears and is substituted by a second magnetization peak (where the characteristic fields are significantly lower) induced by pinning enhancement. The second magnetization peak was clearly seen at high temperatures only, due to the occurrence of thermo-magnetic instabilities in the low-T domain. In both cases, analysis of magnetic relaxation evidences a crossover towards plastic vortex creep accompanying the maximum in the effective critical current density. These results suggest a common nature of the observed effects, related to the disordering of the vortex system induced by pinning.

Controlled hydrothermal synthesis, excellent optical and magnetic properties of CeO2 nanocubes

The CeO2 nanocubes with rough surface have been successfully synthesized by a facile hydrothermal technique. The reaction temperature was systematically investigated. X-ray diffractometer, scanning electron microscope, transmission electron microscope, X-ray photoelectron spectroscopy, Raman scattering, ultraviolet–visible and Photoluminescence spectra, and magnetization hysteresis (M–H) curves were employed to characterize the samples. The results showed that all the CeO2 nanocubes owned a fluorite cubic structure and there are Ce3+ ions and oxygen vacancies in surface of samples. Although the morphology had a slight difference for the samples synthesized at different temperature and the average edge length of the nanocubes increased from ~150 to ~250 nm, then to ~350 nm with the enhancement of temperature, the cube-like morphology remained unchanged. The synthesized CeO2 samples show excellent room temperature optical properties. The M–H curves of CeO2 nano-octahedrons exhibit excellent room-temperature ferromagnetism, which is likely attributed to the effects of the different morphology of samples, Ce3+ ions and oxygen vacancies.

First Observation of Non-Resonant X-Ray Magnetic Diffraction for Multilayers

Co/Pd magnetic multilayers have been prepared by using a sputtering method. Lattice distances and magnetic hysteresis curves have been measured by X-ray diffraction (XRD) measurements and magnetization measurements using a vibrating sample magnetometer (VSM). The XRD measurements have shown that the samples with thinner Pd layers have shorter lattice distances, and the VSM measurements have shown that the samples of thinner Co and thicker Pd layers are closer to those of perpendicular magnetic anisotropy. We have applied the X-ray magnetic diffraction method to the Co/Pd multilayer for the first time and have succeeded in observing a change in the X-ray diffraction intensities by the reversal of the magnetization direction.

Hyperfine interaction and tuning of magnetic anisotropy of Cu doped CoFe2O4 ferrite nanoparticles

Ferrimagnetic oxides may contain single or multi domain particles which get converted into superparamagnetic state near a critical size. To explore the existence of these particles, we have made Mössbauer and magnetic studies of Cu2+ substitution effect in CoFe2−xO4 Ferrites (0.0, 0.1, 0.2, 0.3, 0.4, and 0.5). All the samples have a cubic spinel structure with lattice parameters increasing linearly with increase in Cu content. The hysteresis loops yield a saturation magnetization, coercive field, and remanent magnetization that vary significantly with Cu content. The magnetic hysteresis curves shows a reduction in saturation magnetization and an increase in coercitivity with Cu2+ ion substitution. The anisotropy constant, K1, is found strongly dependent on the composition of Cu2+ ions. The variation of saturation magnetization with increasing Cu2+ ion content has been explained in the light of Neel's molecular field theory. Mössbauer spectra at room temperature shows two ferrimagnetically relaxed Zeeman sextets. The dependence of Mössbauer parameters such as isomer shift, quadrupole splitting, line width and hyperfine magnetic field on Cu2+ ion concentration have been discussed.

GaN FET単相PWMインバータによる高キャリア周波数励磁時の鉄損特性

The Iron loss at higher carrier frequencies up to 190kHz is measured by a single-phase GaN FET inverter because sinusoidal-like waveform is expected to be obtained by new material devices such as those based on SiC or GaN. The measured data show that iron loss excited by PWM inverter does not converge to the iron loss by sinusoidal excitation because the fluctuation in the magnetic field does not converge to zero, even when carrier frequency is 190kHz. Moreover, the iron loss even increases at some carrier frequency for a long dead time. Because of the properties of the GaN FET device, the ON voltage of the GaN FET during the dead time period becomes large, and the minor loop shape in the magnetic hysteresis curve becomes large. These phenomena are observed for a constant applied DC voltage and also for a constant modulation factor constant condition. The properties of the power semiconductor and the dead time of the inverter seriously influence the increase in the iron loss.

In situ fabrication of biphasic-induced magnetic nano-hydroxyapatite chitosan-based composite microcapsules for bone regeneration

Event Abstract Back to Event In situ fabrication of biphasic-induced magnetic nano-hydroxyapatite chitosan-based composite microcapsules for bone regeneration Jingdi Chen1*, Panpan Pan1*, Tiantang Fan1* and Qiqing Zhang1, 2* 1 Fuzhou University, Institute of Biomedical and Pharmaceutical Technology, China 2 Chinese Academy of Medical Science & Peking Union Medical College, Institute of Biomedical Engineering, China Introduction: This research aims to in situ fabricate and investigate the biphasic-induced endogenous magnetic microspheres (BIEMM) as a promising environmental stimuli-responsive delivery vehicle to dispose the problem of drug burst effect. Icariin (ICA), a plant-derived flavonol glycoside, was combined to study drug release properties of BIEMM, which is ascribed to its outstanding function of promoting osteoblasts adhesion and proliferation. The ICA loaded magnetic chitosan/nano hydroxyapatite (CS/nHA/MNP) microcapsules were prepared by the high voltage static microcapsule forming device. Fe3O4 magnetic nanoparticles (MNP) and nHA were in situ crystallized simultaneously by one - step process and BIEMM were characterized. It was governed by the formation mechanism that the amino groups (-NH3) of CS could be used as binding sites for the synthesis of both Fe3O4 MNP and nHA. Therefore, the novel ICA loaded biphasic-induced endogenous CS/nHA/MNP microcapsules are expected to find application in bone regeneration. Materials and Methods: Briefly, moderate CS powder was dissolved in 53 ml of 1 % acetic acid solution stirred for 1 h to form a homogeneous CS solution. The alcohol solution of ICA was added and stirred for 1.5 h magnetically at room temperature, and then added FeCl3·6H2O and FeCl2·4H2O to form 0.15mol·L−1 and 0.075mol·L−1 solution, according the mole ratio of Fe3+/ Fe2+=2, stirred for 45 min, respectively. Similarly, followed by adding Ca(NO3)2·4H2O and K2HPO4 solution according the ratio of Ca/P=1.67, stirred for 3 h, to prepare the BIEMM precursor solution. By the high voltage electrostatic micro capsule forming device, precursor solution was drop-wise added in a 250 ml beaker containing 4 % NaOH aqueous solution (as coagulation bath). The mixtures were thoroughly mixed by occasional shaking and incubated for 12 h at 37 oC to form microsphere. After several cycles of centrifugation at 8,000 rpm for 5 min and washing with deionized water, the media gradually became a neutral and the microspheres were lyophilized for further use. Results and Discussion: Fig. 1 In situ fabrication of BIMCM. (A) Stereoscopic microscope images, (B) SEM images, (C) Cumulative release curves of ICA, (D) Magnetic hysteresis curves of (1) CS/MNP, (2) CS/nHA/MNP and (3) BIMCM. (E) Digital photographs of the dispersion of BIMCM in the separation with an external field (1) and absence of external magnetic field (2). BIMCM with equiaxed and homogeneous morphology were obtained in Fig. 1A. In addition, BIMCM showed relatively porous and rough surface with no obvious collapse structure, as displayed on Fig. 1B. We investigated the morphology of automated in situ click Fe3O4 MNP and nHA particles on the surface structure, which may be closely related to the deposition of Fe3O4 MNP and nHA particles into the BIMCM, as well as the bareness of ICA on the surface of microcapsules[1]. In Fig. 1E, BIMCM could be easily attached to the sidewall from water solution within eternal magnetic field. The successful introduction of the in situ Fe3O4 MNP provided an alternative strategy for ICA sustained release in Fig. 1C. Therefore, the microcapsules possessed magnet-induced sensitivity, indicated the BIMCM could meet the requirement of magnetic drug targeting. Fig. 2 Wright-Giemsa dying assay (A1A2) and AO/EB fluorescent staining (A1B2) for proliferation of osteoblasts cultured with BIMCM for 3 and 5 d, respectively. Wright-Giemsa dying assay (A1A2) and AO/EB fluorescent staining (B1B2) of osteoblasts cultured with BIMCM for 3 and 5 d respectively were depicted, as shown in Fig. 2[2]. Our in vitro toxicity text results demonstrated that BIMCM had a good biocompatibility and could be very conducive to promoting osteoblast proliferation. Conclusion: It can be speculated that the successful introduction of in situ Fe3O4 MNP into bone repair provided a robust platform as a function of the properties of magnetic sensitivity and sustained release. As such, the innovative biphasic-induced ICA loaded CS/nHA/MNP microcapsules were expected to find potential application in drug delivery system and bone repair in the future. This research was supported by National Natural Science Foundation of China (31100677 and 31370958) and Scientific Project of Fujian Education Department (JA14031).

Room temperature growth of ultrathin ordered MnGa films on a CoGa buffer layer

Tetragonal ultrathin (1–5 nm) ordered MnGa films on a CsCl-type CoGa buffer layer were fabricated by a sputtering method. The (001)-CoGa layer was first deposited on a Cr-buffered MgO substrate and then annealed in-situ at 500 °C. The ultrathin MnGa film deposited on the CoGa buffer layer formed the L10 structure with very small roughness even when grown at room temperature. In addition, the films showed well-squared perpendicular magnetization hysteresis curves even when the film thickness was as little as 1 nm. The obtained results are important for the development of the MnGa-based spin-transfer torque devices for Gbit class magnetic random access memory and high frequency applications.