Measured Magnetization Curves Research Articles

Inversion of magnetic diameter distribution of magnetic fluids under high and low temperatures

The magnetic diameter is a crucial factor affecting the magnetic properties of magnetic fluids. The magnetic diameter distribution can be estimated based on the magnetic properties. However, the magnetic dipole interaction of magnetic nanoparticles (MNPs) and the variation of the magnetic diameter with temperature have received relatively little attention in previous research. Hence, this research proposes the AP-MMF1-L method to inverse the magnetic diameter which considers the magnetic dipole interaction and derives the magnetic diameter at different temperatures. Firstly, the AP-MMF1-L uses the least square method between the first-order modified mean-field Langevin function (MMF1-L) and the measured magnetization curve as the objective function. Meanwhile, the hybrid Artificial bee colony-particle swarm (AP) optimization algorithm is introduced to inverse the optimal magnetic diameter distribution. Secondly, the hydrodynamic diameter distribution experimental values are compared with the theoretical values, demonstrating the AP-MMF1-L method obtains accurate inversion results of the magnetic diameter distribution when compared to other models. Finally, the arithmetic mean of the magnetic diameter at different temperatures is investigated, revealing a decreasing trend as the temperature rises, approximately following a linear distribution. The AP-MMF1-L provides a novel and effective tool for accurately determining the magnetic diameter of the MNPs across various temperatures.

A Modification of Magnetic Adaptive Testing: Progressive Method for Nondestructive Inspection of Microstructural Changes in Ferromagnetic Constructional Materials

Magnetic adaptive testing (MAT), thanks to its relative simplicity from the point of view of both hardware and software, appears to be very promising for non-destructive analysis of various ferromagnetic constructional materials used in many industrial applications. In order to make the inspection of tested objects faster, even more straightforward and the processing of data easier, we concentrated our effort both to improve the experimental procedure, based on specific way of the measurement of magnetization curves at piece-wise linear (triangular) exciting field with a constant field rate of change (i.e., slope) as well as to create a universal software tool for MAT data analysis. On contrary to the original implementation of MAT, the hysteresis loops are measured with decreasing maximum field values, starting at sample saturation region; therefore, time consuming sample demagnetization can be skipped completely. In addition, an advanced tool for the processing of experimentally obtained magnetization curves is presented. Using this application allows to find proper non-traditional magnetic parameters (e.g., the differential permeability) being the most sensitive to various types of industrial load (e.g., thermal, mechanical and/or neutron irradiation) and, at the same time, sufficiently correlated with other, traditional magnetic as well as non-magnetic parameters used routinely for the assessment of possible structural changes associated with applied, often long-term, load even on a microscopic scale, prior to any damage manifests on a macroscopic, visible level. The software capabilities were demonstrated on the data representing the material, whose response to acting thermal load is being difficult to analyze, since the dependence of observed parameters (differential permeability) upon defined artificial ageing was rather complicated. Nevertheless, the sensitivity of differential permeability to such a load was found being more than 8 times larger than in case of traditional hysteretic parameter, namely the remanent flux density while the correlation between them was high.

Large-scale vibrating coil magnetometer for the magnetic characterization of bulk superconductors

This work presents the design and validation of a vibrating coil magnetometer for the characterization of the field dependence of the critical current density of centimeter-sized bulk superconductors as an alternative to the destructive methods typically used. The magnetometer is also shown to be capable of measuring the magnetic moment in an applied field of up to 5 T for diverse magnetic materials, such as soft and hard ferromagnets and high-temperature superconducting pellets. The vibrating coil magnetometer was first optimized using finite element simulations and calibrated using a commercial vibrating sample magnetometer. The vibrating coil magnetometer was benchmarked with hysteresis measurements of a Nd2Fe14B disk made with a commercial hysteresisgraph, showing good agreement between the different setups. The magnetic hysteresis of a YBa2Cu3O7−x superconducting pellet was measured at 77 K, showing a penetration field of 1 T and an irreversibility field of 4 T. The field dependent critical current density of the superconductor was then inferred from the magnetic hysteresis measurements and extrapolated at low fields. Finally, the resulting critical current density was used to successfully reproduce the measured magnetization curve of the pellet at 2 T with finite element simulations.

Influence of the hierarchical architecture of multi-core iron oxide nanoflowers on their magnetic properties

Magnetic properties of superparamagnetic iron oxide nanoparticles are controlled mainly by their particle size and by their particle size distribution. Magnetic properties of multi-core iron oxide nanoparticles, often called iron oxide nanoflowers (IONFs), are additionally affected by the interaction of magnetic moments between neighboring cores. The knowledge about the hierarchical structure of IONFs is therefore essential for understanding the magnetic properties of IONFs. In this contribution, the architecture of multi-core IONFs was investigated using correlative multiscale transmission electron microscopy (TEM), X-ray diffraction and dynamic light scattering. The multiscale TEM measurements comprised low-resolution and high-resolution imaging as well as geometric phase analysis. The IONFs contained maghemite with the average chemical composition gamma-Fe_{2.72pm 0.02}O_4. The metallic vacancies located on the octahedral lattice sites of the spinel ferrite structure were partially ordered. Individual IONFs consisted of several cores showing frequently a specific crystallographic orientation relationship between direct neighbors. This oriented attachment may facilitate the magnetic alignment within the cores. Individual cores were composed of partially coherent nanocrystals having almost the same crystallographic orientation. The sizes of individual constituents revealed by the microstructure analysis were correlated with the magnetic particle sizes that were obtained from fitting the measured magnetization curve by the Langevin function.

Spin supersolidity in nearly ideal easy-axis triangular quantum antiferromagnet Na2BaCo(PO4)2

Prototypical models and their material incarnations are cornerstones to the understanding of quantum magnetism. Here we show theoretically that the recently synthesized magnetic compound Na2BaCo(PO4)2 (NBCP) is a rare, nearly ideal material realization of the S = 1/2 triangular-lattice antiferromagnet with significant easy-axis spin exchange anisotropy. By combining the automatic parameter searching and tensor-network simulations, we establish a microscopic model description of this material with realistic model parameters, which can not only fit well the experimental thermodynamic data but also reproduce the measured magnetization curves without further adjustment of parameters. According to the established model, the NBCP hosts a spin supersolid state that breaks both the lattice translation symmetry and the spin rotational symmetry. Such a state is a spin analog of the long-sought supersolid state, thought to exist in solid Helium and optical lattice systems, and share similar traits. The NBCP therefore represents an ideal material-based platform to explore the physics of supersolidity as well as its quantum and thermal melting.

An optimized scheme for detecting magneto-optic effects in ultrathin films with Sagnac interferometry.

Sagnac interferometry is advantageous in measuring time-reversal-symmetry breaking effects in ferromagnetic and antiferromagnetic materials as it suppresses time-reversal symmetric birefringent effects that are ubiquitous and often overwhelming in optical detection systems. When its sensitivity is limited only by the amplifier noise in the photo-detector, one needs to optimize the optical power that returns to the detector. We demonstrate an experimental scheme that maximizes the returning optical power in a Sagnac interferometry when detecting the magneto-optic effect in ultrathin films. In this scheme, the optical beam bearing the Faraday effect on a thin film is reflected at a second surface coated with a highly reflective gold film. The gold film increases the returned optical power by a factor of 4-5. For a normal-incidence Sagnac interferometer, this scheme yields an increase in the signal-to-noise ratio by the same factor. For an oblique-incidence Sagnac interferometer, this scheme should yield an increase in the signal-to-noise ratio by a factor of 20-25. For illustration, this scheme is used to measure magnetization curves and Kerr rotation images of 4.5-unit-cell thick SrRuO3(001) grown on SrTiO3(001).

Magnetization dynamics of iron oxide super paramagnetic nanoparticles above blocking temperature

Magnetic characterizations of synthesized superparamagnetic Iron-Oxide nanoparticles have been carried out at various constant temperatures. As magnetization versus magnetic field (M−H) curve verifies the superparamagnetic nature of nanoparticles, M−H curve has been analysed to verify the superparamagnetic behavior of synthesized nanoparticles. Structure and morphology has been characterized by X-ray diffraction (XRD) and Transmission Electron Microscopy (TEM).The XRD confirms the cubic spinel structure of prepared nanoparticles. Cubical shaped morphology is observed from the TEM image. The reaction temperature is observed to critically affect the particle size and modification of magnetic properties. Further, the M−H curve has been analysed to fit the Langevin function and size distribution of nanoparticles has also been studied. The experimentally measured magnetization curve found to fit the theoretically calculated Langevin function satisfactorily. The typical intrinsic magnetization of prepared nanoparticles show superparamagnetism and observed to follow the sigmoid function with negligible remanence and coercivity value. The particles are found to be agglomerated with a size distribution of 10 - 30 nm.

Magnetoelastic transition and giant anisotropic magnetostriction effect in textured Mn<sub>1.9</sub>Co<sub>0.1</sub>Sb polycrystal

Mn2Sb-based alloys have extremely promising practical applications in many fields owing to their abundant and controllable magnetofuntional properties around the first-order magnetoelastic transition, as well as their low costs. However, only a few studies on the magnetostrain of these alloys have been reported. Herein, a highly textured Mn1.9Co0.1Sb polycrystal is fabricated by using the arc-melting technique, which produces a strong temperature gradient induced by rapid cooling during the arc-melting process, resulting in the highly selective orientation of crystal growth. X-ray diffraction and thermomagnetic measurements show that the grains grow in certain crystallographic directions. Metamagnetic transition is revealed by the isothermal magnetization curve measurements, which is observed to be more obvious at lower temperatures. The standard resistive strain-gauge method is adopted to measure the magnetostriction effect. Giant anisotropic magnetostrain values of up to 0.246% and −0.11% are obtained parallel and vertical to the texture of the alloy, respectively. This magnetostriction effect mainly originates from the anisotropic lattice distortion across the first-order magnetoelastic phase transition.

Dielectric and magnetic properties of holmium and ytterbium titanates

Ytterbium and holmium titanates have been synthesized and their dielectric and magnetic properties have been investigated. The frequency dependences of the permittivity at T = 77 and 300 K, and measured magnetization curves and temperature dependences of the magnetic susceptibility in fields up to 30 kOe and at temperatures from 2 K to 50 K have been obtained. The properties of the doped and undoped titanates have been compared. Based on the temperature dependences of the magnetic susceptibility, the magnetic dipole and exchange couplings in the titanates have been analyzed.

Synthesis and Magnetic Characterization of La<sub>2-</sub><i><sub>x</sub></i>Sr<i><sub>x</sub></i>CuO<sub>4</sub> Nanoparticles

Non-doped and strontium-doped lanthanum cuprates (La2CuO4 (LCO) and La1.85Sr0.15CuO4 (LSCO15)) in nano-sized particles were synthesized by the chemically dissolved technique employing HNO3 as the dissolving agent. The structural and magnetic properties were investigated by using an x-ray diffraction (XRD) apparatus and a superconducting quantum interference device (SQUID) magnetometer, respectively. The XRD patterns of LCO and LSCO15 show the formation of the single phase without impurities after the calcinations in air at 1100°C for 15 h and the post-annealing in oxygen at 800 °C for 24 h. The average crystallite sizes of LCO and LSCO15 samples were in a range of around 100 nm confirming nano-sized particles. The LCO and LSCO15 nanoparticles exhibit superconductivity at the superconducting (SC) transition temperature, Tc, of 23 K and 38 K, respectively. The magnetization curve measurements have revealed that both samples show the appearance of ferro- and dia-magnetic behavior at room temperature and the appearance of superconductivity at low temperatures. This result may indicate the coexistence of ferromagnetism and superconductivity below Tc in the nano-sized cuprates.

Magnetic Property of Thin Film of Co-Tb Alloys Deposited on the Barrier Layer of Ordered Anodic Alumina Templates

Recently, search for novel materials for bit patterned media (BPM) has been very intense due to their potential application in ultra-high-density hard disk drive. In a quest of finding new materials for BPM, we have taken up to study ordered array of nanostructured Co-Tb alloy. Thin films of Ta (1 nm)/Co1−xTbx (24 nm)/Ta (4 nm) (x = 0.10, 0.15, 0.18 and 0.33) alloys were deposited on the barrier layer of auto-assembled anodic alumina template using dc magnetron sputtering to form a nanostructured array, the so-called nanobump. Similar array of compounds on a flat Si substrate was also deposited for comparison (reference sample). The measurement of room temperature magnetization (M) versus field (H) curve indicates that the coercivity and the squareness [Mr/Ms] of nanobumps as well as reference samples were found to increase with increase of Tb content. However, the values of HC and Mr/MS for nanobumps were found to be higher than those of reference samples. The measurements of in-plane and out-plane M-H curves reveal that Co1−xTbx (x = 0.15, 0.20 and 0.33) nanobumps exhibit magnetic isotropy behaviour. The measurements of temperature variation of magnetization demonstrate that these films exhibit ferrimagnetism with a compensation temperature much above the room temperature.

Performances of a Compact Shielded Superconducting Magnet for Continuous Nuclear Demagnetization Refrigerator

We have successfully developed and tested a compact shielded superconducting (SSC) magnet with a FeCoV magnetic shield. This was developed for the PrNi$_5$ based nuclear demagnetization refrigerator which can keep temperatures below 1 mK continuously (CNDR) [Toda $\it{et~al}$., J. Phys.: Conf. Ser. $\bf{969}$, 012093 (2018)]. The clear bore diameter, outer diameter, and total length of the SSC magnet are 22, 42 and 169 mm, respectively, and it produces the maximum field of 1.38 T at an electric current of 6 A. In order to realize both the compactness and the high shielding performance, we carefully chose material and optimized design of the magnetic shield by numerical simulations of the field distribution based on measured magnetization curves of several candidate materials with high permeability. We also measured a heat generated by sweeping the SSC magnet in vacuum to be 230 mJ per field cycle. This value agrees very well with an estimation from the measured magnetic hysteresis of the superconducting wire used to wind the magnet.

Determination of stress dependent magnetostriction from a macroscopic magneto-mechanical model and experimental magnetization curves

In this paper, we propose a method to identify the magnetostrictive behavior of electrical steel sheet submitted to a mechanical loading. The technique relies on the use of a magneto-mechanical model including the magnetostrictive phenomenon, namely the anhysteretic Jiles-Atherton-Sablik (JAS) model, and experimental macroscopic stress dependent magnetization curves. The method is illustrated with measured magnetization curves of a non-oriented (NO) electrical steel sheet under different stresses. Furthermore, the influence of a bi-axial mechanical loading on the magnetostrictive behavior is analyzed with the help of an equivalent stress.

Magnetic transitions in delafossite CuFeO2: A magnetocaloric effect study

CuFeO2 was synthetized by a solid-state reaction and its low temperature magnetic properties were investigated using the magnetocaloric effect. Magnetic susceptibility measurements show that there are two magnetic transition temperatures at about 16 and 11 K. Measurement of isothermal magnetization curves for different applied magnetic fields near these temperatures show a reversal in the magnetization trend around 16 K, and Arrott plots indicate they are accompanied by second- and first-order magnetic phase transitions, respectively. Both normal and inverse magnetocaloric effects are observed, and the maximum magnetic entropy change is obtained at 11 K.

On the correlation of crystallographic macro-texture and magnetic magnetization anisotropy in non-oriented electrical steel

Abstract In material models for the finite-element simulation of electrical machines and the preceding magnetic measurements, the magnetic anisotropy of non-grain oriented electrical steel is usually considered in an oversimplified way, if at all. The magnetization behavior between rolling and transverse direction is not linear and varies with magnetic polarization, a relation that comes in addition to the complexity of the effect. In this paper, the magnetization anisotropy of five industrial non-grain oriented electrical steels is measured with a 1-D single-sheet-tester. The results are evaluated and correlated to the crystallographic texture of the studied materials. An approach to model magnetization curves at 50 Hz in arbitrary directions of the sheet plane is presented. The model is parametrized by measured magnetization curves along three different spatial directions and by macro-texture data in form of an orientation distribution function. This approach leads to a model that replicates the crossing of magnetization curves of different orientations with adequate quantitative accuracy for the application in FE magnetic field simulations.

The Design of Flux Linkage Measurement for Switched Reluctance Motor

A Back Propagation neural network (BPNN) flux linkage model was proposed based on the measured magnetization curve for 8/6 poles switched reluctance motor (SRM). A flux linkage measuring installation is set up by using a digital signal processor (DSP) and measuring the voltage of winding under different rotor positions and different current values, then obtained the value of the corresponding flux linkage and the rotor magnetization characteristics of different positions.The flux linkage has higher accuracy. The design has the actual reference value to the high performance speed control of SRM.

Magnetization plateaus and phase diagrams of the extended Ising model on the Shastry-Sutherland lattice: effects of long-range interactions

Magnetization plateaus and phase diagrams of the extended Ising model on the Shastry-Sutherland lattice with the first $(J_1)$, second $(J_2)$, third $(J_3)$ fourth $(J_4)$ and fifth $(J_5)$ nearest-neighbour spin couplings are studied by the classical Monte Carlo method. It is shown that switching on $J_4$ and $J_5$ interactions (in addition to usually considered $J_1, J_2$ and $J_3$ interactions) changes significantly the picture of magnetization processes found for $J_4=J_5=0$ and leads to stabilization of new macroscopic magnetic phases (plateaus) with fractional magnetization. In particular, it is found that combined effects of $J_4$ and $J_5$ interactions generate the following sequence of plateaus with the fractional magnetization: $m/m_s$=1/9, 1/6, 2/9, 1/3, 4/9, 1/2, 5/9 and 2/3. The results obtained are consistent with experimental measurements of magnetization curves in selected rare-earth tetraborides.

Analytical Functions of Magnetization Curves for High Magnetic Permeability Materials

In this paper, combined rational and power functions are used to represent magnetization curves of high magnetic permeability ferromagnetic materials. The proposed functions cover much wider range of magnetic fields than functions currently used in simulation software packages. The objective is to present simple functions for approximation of magnetization curves with minimum number of unknown constants. The calculated functions are finally compared with measured magnetization curves to validate the precision in a wide field range from 10−2 to 106 A/m.

Anhysteretic Magnetization Measurement Methods for Soft Magnetic Materials.

This article is concerned with the methods for experimentally determining the Anhysteretic Magnetization curve for soft magnetic materials. A new method based on the modern hysteresisgraph system is presented. Known modern and traditional methods based on fluxmeters are presented as well. The experimental results obtained with the described methods for isotropic Mn–Zn ferrite are compared. Lastly, results of validation on NANOPERM® nanocrystalline material are detailed and show negligible hysteresis. The new method allows for accurate Anhysteretic Magnetization curve measurement without software or hardware modifications of standard, commercially available hysteresisgraph systems. The speed and accuracy of the results are improved in comparison with other methods.

Strain effects on the magnetic order of epitaxial FeRh thin films

In this work, we report the experimental results obtained on a set of ∼90 nm thick FeRh epitaxial films deposited on MgO (001), MgO (111), and Al2O3 (0001) single crystal substrates. The magnetic characterization was achieved by measuring magnetization curves and ferromagnetic resonance as a function of temperature and orientation of the films with respect to the applied magnetic field. We discuss our results by comparing the characteristics of the antiferromagnetic-ferromagnetic transition among FeRh films of the same thickness but exposed to different post-growth annealings and deposited on substrates of different crystalline orientations. We have found that there is a correlation between the strain present in the films and their magnetic behavior, observing that a change in the in-plane stress from compressive to tensile tends to shift the magnetic transition by more than 60 K. The interplay between magnetic and elastic properties was further analyzed by ferromagnetic resonance, and we have found that the magnetoelastic component of the anisotropy varies from out-of-plane to in-plane, depending on the substrate. These findings could be of great importance if a precise tuning of the magnetic transition temperature or the magnetic anisotropy is needed for a specific application.