Hysteresis Loop Measurements Research Articles

Anomalous ferroelectricity and strong magnetoelectric coupling in CoFe2O4-ferroelectric composites

A unique averaging mechanism is established for estimation of magnetoelectric coupling coefficient (α) by studying the effect of magnetic field on ferroelectric hysteresis loop measurements. The highest value of α obtained using this mechanism is 22 mV/cm/Oe at a field of 5000 Gauss for CoFe2O4-10%BaTiO3 (CFO-10BT) composite and is in agreement with the recent reported studies. The composites of CFO-BT exhibit interplay of magnetism, ferroelectricity and display strong magnetoelectric behaviour arising out of charge disordering. The structural studies from the combination of XRD, Raman and FTIR measurements of CFO-BT composites establishco-existence of cubic and tetragonal phase with space group. The ferroelectric studies display a low leakage charge density of 0.0031 μC/cm2 and prevalent asymmetry arising due to spatial disordering of charge distribution. Furthermore, the magnetic measurements reveal an enormous increase in the coercivity of CFO-30BT composite which is identified in terms of movement of ferromagnetic domains arising due to inclusion of trapping centres of BT in CFO.

High temperature corrosion of Fe‐6 wt% Si steel in various atmospheres

Corrosion of Fe‐6Si steel during heat treatment at 500 and 700 °C in air, argon, and vacuum was studied. Phase and structure analysis were carried out using Mössbauer spectroscopy, X‐ray diffraction, scanning electron microscopy, Glow discharge optical emission spectrometry, and X‐ray photoelectron spectroscopy. Measurement of magnetic hysteresis loops were used to follow changes in magnetic properties. Structure and phase composition of surface layers change in dependence on annealing conditions. Besides the content of hematite, magnetite, and fayalite an increase in silicon content at the surface was detected namely after annealing at 700 °C. Our results show that good magnetic properties of the studied Fe‐6 wt% Si steel are not deteriorated substantially by annealing at 500 and 700 °C in air, argon, and vacuum. Therefore this steel can be applied in magnetic circuits working at high temperatures.

Deciphering magnetic hyperthermia properties of compositionally and morphologically modulated FeNi nanoparticles using first-order reversal curve analysis

Magnetic hyperthermia based on nanoparticles (NPs) is considered a significant approach in cancer therapy. However, less attention has been paid to the correlation between hyperthermia properties and detailed magnetic characteristics. Herein, the hyperthermia capability of FexNi100-x (8 ≤ × ≤ 40) NPs synthesized using a polyol method was studied by investigating the temperature rise and specific loss power (SLP) of their ferrofluid (FF) solutions while also performing first-order reversal curve (FORC) analysis. The colloidal stability of magnetic NPs in the FFs was enhanced by coating their surface with polyethylene glycol, and the hyperthermia experiments were carried out in ethylene glycol and DI water (DIW) dispersion media using different concentrations (1.25, 2.5 and 5 mg ml−1). A field-emission scanning electron microscope was employed to characterize the morphology of the FeNi NPs, evidencing mean diameters ranging between 64–112 nm. Hysteresis loop measurements showed a decreasing trend of average coercive field from 94 to 52 Oe when decreasing the diameter, coinciding with a 13% increase in the reversible fraction of single-domain and superparamagnetic (SP) NPs, according to FORC results. In this way, the corresponding SLP value increased from 55 to 264 W g−1 for FFs in 1.25 mg ml−1 concentrated DIW medium with an SP fraction of 40%.

Effect of Tilted Magnetic Anisotropy on the Deterministic Current-Induced Magnetization Reversal in Quasi-Perpendicularly Magnetized Ta/Pt/CoFeB/Pt Multilayers

Deterministic current-induced magnetization reversal is observed in quasi-perpendicularly magnetized Ta/Pt/CoFeB/Pt multilayer thin films without the assistance of an in-plane field. In a quasi-perpendicularly magnetized system, the anisotropy is tilted slightly away from the normal to the film plane. This tilt in the anisotropy is obtained by growing the films in an oblique-angle sputter deposition technique, which results in a gradient in the thickness of the layers. To estimate the tilt, out-of-plane hysteresis loop measurements are performed in the presence of an in-plane bias field. The effect of the tilt is reflected in the shift in the hysteresis loop. A measurement of this shift at different relative azimuthal orientations of the in-plane projection of the tilt direction with respect to the in-plane bias field direction gives a tilt of 0.74° (±0.06°) in Ta(3 nm)Pt(3 nm)CoFeB(0.5 nm)Pt(1 nm) with all the layers having a thickness gradient. In addition, field-induced domain wall velocity measurements in the creep regime on Ta(3 nm)Pt(3 nm)CoFeB(0.5 nm)Pt(1 nm) thin film with a thickness gradient only in CoFeB layer give an elliptical profile for the domain wall. In the current-induced magnetization reversal studies, threshold current density of $1.06 \times 10^{11}$ Am−2 is required to deterministically switch the device fabricated from Ta(3 nm)Pt(3 nm)CoFeB(0.5 nm)Pt(1 nm) thin film with all the layers having a thickness gradient. On application of in-plane bias, there is a shift in the threshold current densities given by $2.6 \times 10^{8}$ Am−2 of in-plane bias field.

Magnetic field induced polarization and magnetoelectric effect in Na0.5Bi0.5TiO3–Co0.75Zn0.25Cr0.2Fe1.8O4 multiferroic composite

Abstract Multiferroic composites of Zn-Cr substituted cobalt ferrite (Co0.75Zn0.25Cr0.2Fe1.8O4) (CZCFO) nanoparticles and lead-free piezoelectric sodium bismuth titanate Na0.5Bi0.5TiO3 (NBT) having composition (1 − x) Na0.5Bi0.5TiO3 + (x)Co0.75Zn0.25Cr0.2Fe1.8O4 (x = 0.0, 0.25, 0.5, 0.75, 1.0) were investigated in this study. Ferromagnetic-CZCFO and ferroelectric-NBT phases were synthesized via sol-gel auto combustion route and solid-state reaction methods respectively. The structural properties of composite materials were studied using X-ray diffraction (XRD) technique. Intense and sharp peaks observed in XRD patterns confirm that both the phases are well crystalline in nature. Two separate phases of CZCFO and NBT are present in composite material without any impurity or chemical reaction among them. The morphology of prepared samples was studied via scanning electron microscopy confirming that composite materials are well-densified and homogenous grain size distribution. The magnetic hysteresis loops of multiferroic composite were investigated by using vibrating sample magnetometer at room temperature. The lead free multiferroic composite exhibiting a large converse magneto-electric (ME) effect at room temperature. The maximum value of ME coefficient (αME = 7.92 kV/cm) is obtained at x = 0.50. Furthermore, electrical properties of nanocomposite material were studied by P-E hysteresis loop and dielectric measurements at room temperature.

Numerical modelling of shear hysteresis of entangled cross-linked carbon fibres intended for core material

The analysis of an entangled cross-linked fibrous material at low deformation is explored as way of predicting the shear behaviour, especially the shear hysteresis. This paper presents a 3D finite element model to characterize the carbon fibre network rigidified by epoxy cross-links. The morphology of the representative volume element (RVE) is studied to guarantee that it is representative of the actual material that was characterized experimentally. Two steps are simulated, namely the initial compression during the shaping and before the polymerization of the epoxy resin and the cyclic shear testing of the material with its rigidified network of fibres. A numerical simulation of an RVE is used to present a description of the measured hysteresis loop that is decomposed of linear and nonlinear parts. A comparison between the numerical prediction and the experiment data is discussed. Even if the 3D numerical model under-predict the average shear stiffness of the material, it can capture the complex shapes of the measured hysteresis loops at different strain amplitudes.

Exchange bias effect in a finite site disordered canted antiferromagnet

We report the temperature and magnetic field dependent magnetic properties of the single-phase polycrystalline La0.8Sr0.2Cr0.7Ru0.3O3 sample to explore the intrinsic magnetic phases of the sample. Our combined temperature and field dependent magnetization studies reveal the formation of ferromagnetic (FM) cluster-glass in the antiferromagnetic (AFM) matrix of host LaCrO3. Interestingly, the as-studied sample exhibits both zero-field-cooled (horizontal shift) and field-cooled (vertical shift) exchange bias effects and, in both cases, magnitude of exchange bias field continuously increases with the decrease of temperature. Our successive hysteresis loop measurements completely ruled out the effect of any minor hysteresis loop and thus, establishes this vertical shift as conventional field-cooled exchange bias (CEB) effect, originating from the uncompensated spins of randomly substituted canted AFM spin structure. A significantly larger value of CEB field (7.5 kOe) at 5 K is achieved for a cooling field of 50 kOe, not usually observed in conventional FM/AFM interfacial exchange-bias systems.

Interaction plots obtained from in-field magnetization instead of remanence measurements

The great majority of experimental studies on magnetic interactions employ a technique based on the Wohlfarth’s relation and require an initially demagnetized state. In the present work a relation analogous to that of Wohlfarth though between in-field magnetization curves instead of remanence curves is derived. This allowed to introduce interaction plots obtained via measurements of the major hysteresis loop and a recoil curve only. The method is effectively tested on three real magnetic systems which evidence different interaction effects. Although the plots introduced here seem to provide information about interactions alike the classical remanence plots, they present important advantages. These plots are acquired in an easier and faster manner and do not demand demagnetization, which significantly simplifies the measurement procedure and allows assessment of interaction effects in virtually impossible to demagnetize systems with rectangular major loops. Furthermore, this method can easily be adapted for estimation of effects leading to deviations from theoretical behavior of other hysteretic quantities.

Novel magnetically retrievable Bi2WO6/magnetic carbon nano-onions composite with enhanced photoactivity under visible light

The novel magnetically retrievable Bi2WO6/MCNOs (MCNOs, magnetic carbon nano-onions) composite was synthesized via a simple hydrothermal method. The characteristics of the as-prepared materials were explored by XRD, Raman, SEM, TEM, XPS, UV–vis DRS, N2 adsorption-desorption techniques and FT-IR techniques, and the paramagnetic nature of the as-prepared composite was determined by hysteresis loops measurements. In this work, rhodamine B (RhB), methyl orange (MO), methylene blue (MB), tetracycline (TC) and p-nitrophenol (PNP) were chosen as the typical organic pollutants to evaluate the photodegradation efficiency of the as-prepared composite. The results indicated that Bi2WO6/MCNOs have a superior performance on photocatalytic activity than pure Bi2WO6. Furthermore, a possible mechanism was proposed based on the physic-chemical and photocatalytic properties. This work will provide new methodology for designing next generation photocatalyst for environmental purification.

Strong correlations between Structural and Magnetic Properties of Zn and Zr Substituted CuFe2O4 for Magnetic Temperature Controller applications

The effects of tetravalent and divalent substitution on the physical properties of Cu ferrites prepared by double sintering ceramic technique have been investigated. It was found that substitution of Zn and Zr enhanced simultaneously sintering process and crystallization. The initial permeability drops sharply at certain temperature for stoichiometric composition, which make Zn/Zr co-doped NiFe2O4 spinel ferrites a very promising candidate for magnetic switch, magnetic temperature transducer (MTT) and temperature sensitive controller devices. So we can control the change of Curie temperature by simply controlling the contents of Zn and Zr within CuFe2O4. From magnetic hysteresis loop measurements, magnetic moment increases by Zn and Zr substitution. The chemical composition heat treatment and type of substituted ions affect the intrinsic parameters of ferrites such as magnetization, initial permeability, Curie temperature, grain size and structural properties strongly [1]. The hysteresis loop is influenced by defects that retard the magnetic domain wall motion within the grains [2]. CuFe2O4 compound is a sheep material and has important magnetic and electrical properties for various technological applications. The affect of Zn and Zr additives on the structure and magnetic properties of LiZnFe2O4 were reported [3].

MEASUREMENTS OF HYSTERESIS LOOPS OF THE MICROWIRES FIXED IN STRETCHED STATE USING THE VIBRATION MAGNETOMETRY

We present a technique of measuring hysteresis loops of the amorphous microwires using a method of vibrating-sample magnetometry. Control magnetic measurements were carried out on samples of an amorphous microwire of Fe 75 B 13 Si 10 C2 composition in a glass shell obtained by the Ulitovsky – Taylor method. The sample was fixed on a specially manufactured experimental setup which enables us to stretch the microwire by means of suspended loads. Fixation of the microwire in the stretched state was carried out by the glue. The stresses in the metal core of the microwire formed upon stretching with suspended loads, as well as the stresses in the contact area of the wire and glue are calculated. The developed method provides fixing of tensile stresses in wires even when the value of stresses may attains a few GPa.

Magnetic Properties of Rapid Cooled FeCoB Based Alloys Produced by Injection Molding

The paper presents the results of investigations of the structure and magnetic properties of massive rapid cooled Fe50-xCo20+xB20Cu1Nb9 alloys (where x = 0, 5). Massive alloys were made using the method of injecting a liquid alloy into a copper mold. Samples were obtained in the form of 0.5 mm thick plates. The structure of the obtained samples was examined using an X-ray diffractometer equipped with a CuKα lamp. The phase composition of the alloys formed was determined using the Match program. By using Sherrer’s dependence the grain sizes of the identified crystalline phases were estimated. Using the Faraday magnetic balance, the magnetization of samples as a function of temperature in the range from room temperature to 850K was measured. Magnetization of saturation and value of the coercive field for the prepared alloys were determined on the basis of magnetic hysteresis loop measurement using the LakeShore vibration magnetometer.

Magnetic Hysteresis Loop Technique as a NDE Tool for the Evaluation of Microstructure and Mechanical Properties of 2.25Cr–1Mo Steel

This study intends to understand the effect of short-term overheating on microstructure modifications, and variation in mechanical and magnetic properties of boiler tubes. It is based on the hypothesis that short-term overheating on boiler tubes leads to microstructural changes degrading their mechanical properties, thus resulting in their failure. As part of this study, fresh 2.25Cr–1Mo boiler tube samples were heat treated in the range of 700–950 $$^{\circ }\hbox {C}$$ . Magnetic hysteresis loop (MHL) measurements were carried for the non-destructive evaluation (NDE) of the mechanical properties that get altered due to microstructural modifications. For comparison, MHL was also carried out on a service-exposed boiler tube, which had failed due to short-term overheating. The magnetic parameters were correlated with the change in microstructure and micro-hardness of the samples. A decrease in coercivity, remanence, maximum induction and micro hardness were found at the lower soaking temperatures, due to: easy magnetic domain wall and dislocation motions for the stress relaxation; annihilation and recovery of dislocations; increase in inter carbide distance; and the decrease in the number density of carbides for the coarsening of carbides. A subsequent increase in coercivity, remanence and maximum inductions along with hardness are due to the nucleation and growth of fresh bainitic phase, obstructing the magnetic domain wall and dislocation motion. A drastic decrease in coercivity for the service-exposed tube is due to the transformation of MX type carbides to $$\hbox {M}_{23}\hbox {C}_{6}$$ type and accumulation of such carbides at the grain boundaries along with the decrease in number density of the carbides. The presence of scale has less effect on the coercivity, but its demagnetizing effect largely decreases the remanence and maximum induction. The results of the study show that the MHL can be a suitable NDE technique for the evaluation of change in microstructure and degradation of mechanical properties in power plant steels.

Nondestructive magnetic inspection of spot welding

A method of Magnetic adaptive testing (MAT), which is based on systematic measurement and evaluation of minor hysteresis loops is suggested as simple, reliable and sensitive characterization of welded spots. The method is based on the fact that the welding process has a great influence on the microstructure of the welded area, which modifies the magnetic properties. A series of welded spots, produced by different energy of welding current on car-body sheets was investigated. Good correlation was found between the result of destructive characterization and nondestructive magnetic descriptors.

Design of a multifunctional sample probe for transport measurements

We describe a multifunctional sample probe for transport measurements, equipped with a two-axis goniometer providing computer controlled 360${^\circ}$ out of plane and manual 360${^\circ}$ in-plane rotation. The multifunctional sample probe has been successfully implemented to a host dewar and electromagnet system. The developed probe is capable of performing transport measurements and device characterizations with high flexibility of controlling magnetic and electrical fields, angle, temperature and current/voltage parameters in a wide range. The design of the multifunctional sample probe allows easy connection of other external devices and easy installation into other dewar and magnet systems. A software interface based on NI Labview visual programming language has been developed to control the system. The setup has been tested in the hysteresis loop measurements of perpendicularly magnetized Co/Pt/CoO ultra-thin films with anomalous Hall effect (AHE) method. We have also performed temperature dependent exchange bias measurements of the samples. The developed probe revealed much better resolution in the case of perpendicularly magnetized ultra-thin Co/Pt/CoO films compared to a standard vibrating sample magnetometry system.

Comparing the Effects of Nb, Pb, Y, and La Replacement on the Structural, Electrical, and Magnetic Characteristics of Bi-Based Superconductors

In this study, the effects of Pb, Nb, La, and Y replacements were investigated on Bi-based superconducting materials. In preparing the samples, we used a method called solid-state reaction method. The patterns of the X-ray diffraction of all samples indicated presence of Bi-2212 and Bi-2223 phases. The results obtained from XRD revealed that with increase of the melting point of substation elements, the Bi-2223 phase decreased while the Bi-2212 phase and impurity phases of samples grew. From the electrical resistivity measurements using the four-probe method, it was found that sample A with Pb and sample B with La replacements had the maximum and minimum critical temperatures of 111.4 and 81.6 K, respectively. Based on hysteresis loop (M–H) measurement using Bean’s model, estimation of critical current density (Jc) showed that sample A with Pb and sample B with La substitution had the maximum and minimum values respectively. These results may be due to the melting point of these elements with values of 888, 1512, 2315, and 2425 ∘C for PbO, Nb2O5, La2O3, and Y2O3, respectively. These elements were replaced by Bi2O3 with a melting point of 817 ∘ C. Further, the samples were prepared at the temperature of 845 ∘C. It seems at this temperature, these elements not only dissolve within the main matrix and participate in the formation of the Bi-2212 phase during the sintering process but they also participate in the development of the variety of the impurity phases as confirmed by XRD results.

Investigation of defects dependence of local piezoelectric response on Fe, La-modified (Pb,Sr)TiO3 thin films: A piezoresponse force microscopy study

In this study, undoped-(Pb,Sr)TiO3 and Fe3+, La3+ co-doped (Pb,Sr)TiO3 thin films were investigated at the nanoscale level by piezoresponse force microscopy (PFM), in order to evaluate the impact of doping-induced damages on the ferroelectric and piezoelectric properties. Detailed investigations with nanoscale resolution have revealed occurrence of abnormal domains in writing pattern under forward and reverse bias for (Pb,Sr,La)(Ti,Fe)O3 thin films. Further piezoresponse hysteresis loop measurements show that fully switchable loops were observed under high voltage mediated by defect dipoles and by “ferroelectric-like” polar defects clusters. They have been discussed taking into account charged defect formation with both local changes in the dipole moment and local symmetry breaking effects. In addition, the domain writing and its retention behavior of the undoped-PST and (Pb,Sr,La)(Ti,Fe)O3 thin films were investigated. Undoped-PST films exhibited better stability for both positive and negative domains for a relatively long time in comparison to that observed for (Pb,Sr,La)(Ti,Fe)O3 films.

Structure and Magnetism of Mn₅Ge₃ Nanoparticles.

In this work, we investigated the magnetic and structural properties of isolated Mn5Ge3 nanoparticles prepared by the cluster-beam deposition technique. Particles with sizes between 7.2 and 12.6 nm were produced by varying the argon pressure and power in the cluster gun. X-ray diffraction (XRD)and selected area diffraction (SAD) measurements show that the nanoparticles crystallize in the hexagonal Mn5Si3-type crystal structure, which is also the structure of bulk Mn5Ge3. The temperature dependence of the magnetization shows that the as-made particles are ferromagnetic at room temperature and have slightly different Curie temperatures. Hysteresis-loop measurements show that the saturation magnetization of the nanoparticles increases significantly with particle size, varying from 31 kA/m to 172 kA/m when the particle size increases from 7.2 to 12.6 nm. The magnetocrystalline anisotropy constant K at 50 K, determined by fitting the high-field magnetization data to the law of approach to saturation, also increases with particle size, from 0.4 × 105 J/m3 to 2.9 × 105 J/m3 for the respective sizes. This trend is mirrored by the coercivity at 50 K, which increases from 0.04 T to 0.13 T. A possible explanation for the magnetization trend is a radial Ge concentration gradient.

Dielectric and Ferroelectric Properties of Rare Earth Doped Lead Zirconate Titanate Ceramics

We have synthesized La3+ and Sc3+ doped lead zirconate titanate electroceramics with the stoichiometric formula ( (PLZTS), where x = 0.1 and y = 0.2, 0.4, 0.6 & 0.8, by a conventional solid-state reaction method & investigated its structural, microstructural, dielectric, electrical and ferroelectric properties. X-ray diffractometry was used to probe the phase purity and to derive the crystallographic parameters. Furthermore, structural phase transition was investigated by analyzing Raman spectra recorded in the temperature window of 80-580 K. The size, shape, and the distribution of grains were examined through a scanning electron microscope (SEM) and the sample was subjected to energy dispersive spectroscopy (EDS) for elemental analysis. We have carried out dielectric and electrical measurements on Pt/PLZTS/Pt metal-ferroelectric-metal capacitors using impedance analyzer and electrometer, respectively, as a function of temperature (100-600 K) and frequency (102-106 Hz). High dielectric constants (ɛ’) ~280, ~500, ~1800 & 1000 for y = 0.2, 0.4, 0.6 & 0.8 respectively were observed at room temperature. We measured hysteresis loops which proved the existence of ferroelectricity in all prepared samples of different compositions. These results provide insights into PLZTS ferroelectric capacitor for its potential applications in the future electronic devices.

Synthesis of nanocrystalline Ca2Cu2Fe12O22 Y-type hexaferrites by the sol–gel combustion method in metal nitrates system

ABSTRACTNano-size Y-type hexaferrites powders are synthesized by using the sol–gel combustion method in nitrate urea systems. The spectra of FTIR, TGA, and DSC indicate that urea acid and nitrate ions were decomposed at the temperature between 170°C and 200°C. The X-ray diffraction patterns of Ca2Cu2Fe12O22 annealed above 800°C manifest that all the species have hexagonal crystal structure. TEM observation of as-burnt powders of Ca2Cu2Fe12O22 shows the powder particles have an average particle size of 70 nm. Magnetic hysteresis loop measurements of the series Ca2Cu2Fe12O22, exhibit that the saturation magnetization (Ms), the remanent magnetization (Mr) and the coercitivity (Hc) of compounds depend strongly on the chemical composition of materials. The maxium values of Ms (0.54526 emu/g) and Mr (87.099E-3 emu/g) and the areas of magnetic hysteresis loop of compounds decrease with increasing the value of Cu.