Magnetic Hysteresis Loss Research Articles

Tuning the magnetic transition and magnetocaloric effect in Mn1-xCrxCoGe alloy ribbons

The Mn1-xCrxCoGe (x = 0.01, 0.015, 0.02, 0.03) alloy ribbons are prepared. The microstructure, structure, magnetic and magnetocaloric properties were studied in these ribbons. The substitution of Cr for Mn effectively reduces the structural transformation temperature of MnCoGe alloy. In annealed Mn0.98Cr0.02CoGe ribbons, a coupled magnetostructural transformation from the ferromagnetic TiNiSi-type to paramagnetic Ni2In-type state with the increasing temperature is observed. As a result, large magnetocaloric effect near room temperature and simultaneously almost zero magnetic hysteresis losses presented in these ribbons would be favorable to room-temperature magnetic refrigeration. In measuring the isothermal magnetization curves, both the loop and standard methods are adopted to compare and make sure the reliability of our results.

An experimental study of the operating characteristics of an asynchronous motor with pulse supply

The fundamentals of design procedure of performance data of controlled asynchronous motors (AMs) supplied with pulse voltage are stated in this article. The proposed model is based on a L-shaped equivalent circuit for each of harmonics, on which the curve of applied to a phase voltage is displayed. It is proposed to find the increase of magnetic iron loss caused by hysteresis in proportion to the peak value of the pulse voltage. The influence of PWM voltage on magnetic hysteresis loss is determined by using a coefficient depending on the effective values of fundamental and higher harmonics of the EMF and voltages, as well as the coefficient taking into account the increase of electrical resistance of iron due to the skin effect. In a similar way, it is proposed to take into account magnetic losses in the rotor that are occasioned only by the influence of higher harmonics. It is proposed to determine the increase of resistance and decrease of the inductance of short-circuited rotor of the influence of currents of higher harmonics by the well-known Interelectro methodology. The resulting values of consumption current, power factor, effective power, and consumption power of an asynchronous motor with pulse voltage are calculated taking into account the total effect of currents and voltages of fundamental and higher harmonics. Based on the methodology that we have laid out, a program was written and modeling was carried out of the operational characteristics of an asynchronous motor with a power of 180 W supplied by a PWM inverter with a fundamental frequency of 50 Hz. In addition, the harmonic composition of pulse voltage was obtained by processing the oscillograms taken from phase windings of the motor supplied by the frequency converter. To experimentally check of the proposed model, an experimental plant for loading the asynchronous motor was assembled and the operational characteristics of asynchronous motor with the fundamental harmonic of 50 Hz were determined. The experimental results showed satisfactory convergence with the calculated results that makes it possible to recommend the proposed methodology to evaluate the energy indices of frequencycontrolled asynchronous motors.

Improvement of magnetic hysteresis loss, corrosion resistance and compressive strength through spark plasma sintering magnetocaloric LaFe11.65Si1.35/Cu core-shell powders

LaFe11.65Si1.35/Cu core-shell powders were achieved by self-designed magnetron sputtering system, which presents a better solidification during spark plasma sintering in comparison to the naked LaFe11.65Si1.35 powders. Much higher compressive strength, lower corrosion current density and magnetic hysteresis losses are achieved for the sintered sample of LaFe11.65Si1.35/Cu core-shell powders without significant decrease of the magnetic entropy change. The compressive strength, corrosion current density and maximum magnetic hysteresis losses are 105.6 MPa/16.8 MPa, 1.08 × 10−3A/cm2/3.03 × 10−3 A/cm2 and 1.33 J/kg/2.71 J/kg, respectively for the sintered samples of core-shell structured/naked powders. The technique of fabricating the core-shell structured powders demonstrated here is also applicable for other types of functional powders.

Facile synthesis of Fe@Fe2O3 nanochains exhibiting high heating efficiency in magnetic hyperthermia

Ferromagnetic nanoparticles (NPs), with high heating efficiency, have great potential as heating elements for use in magnetic hyperthermia and thermoablation therapies. In this work, core@shell structured Fe@Fe2O3 nanochains were prepared by facile chemical reduction of Fe2+ ions in aqueous solution. The resulting nanochains were characterized by X-ray powder diffraction(XRD), scanning electron microscopy(SEM), transmission electron microscopy(TEM), elemental mapping, Raman analysis, and magnetization measurements. It was found that Fe nanochains form through connection of Fe nanospheres one by one and are coated by amorphous Fe2O3 layer. The chains are about 50–100 nm in diameter and several micrometers in length. Magnetic measurements revealed that as-prepared nanoconstructs possess typical ferromagnetism with a characteristic blocking temperature above 400 K. The saturation magnetization of the samples prepared at 25 °C, 40 °C and 80 °C are 118.6, 81.9, 22.8 emu/g and the coercivity are 136, 259 and 411Oe, respectively. It was interesting to find that these nanochains, dispersed in water at physiological pH, present higher heating efficiency than that of superparamagnetic ferrite NPs. The enhanced heating performance of Fe@Fe2O3 nanochains may be attributed to the activation of a magnetic hysteresis loss mechanism. This study indicates that the resulting Fe@Fe2O3 nanochains are promising materials in magnetic hyperthermia and thermoablation therapies.

Modeling of Hysteresis Losses in Ferromagnetic Laminations Under Mechanical Stress

A novel approach for predicting magnetic hysteresis loops and losses in ferromagnetic laminations under mechanical stress is presented. The model is based on combining a Helmholtz free-energy-based anhysteretic magnetoelastic constitutive law to a vector Jiles–Atherton hysteresis model. This paper focuses only on unidirectional and parallel magnetic fields and stresses, albeit the model is developed in a full 3-D configuration in order to account also for strains perpendicular to the loading direction. The model parameters are fitted to magnetization curve measurements under compressive and tensile stresses. Both the hysteresis loops and the losses are modeled accurately for stresses ranging from −50 to 80 MPa.

Large reversible magnetocaloric effect in a Ni-Co-Mn-In magnetic shape memory alloy

Reversibility of the magnetocaloric effect in materials with first-order magnetostructural transformation is of vital significance for practical magnetic refrigeration applications. Here, we report a large reversible magnetocaloric effect in a Ni49.8Co1.2Mn33.5In15.5 magnetic shape memory alloy. A large reversible magnetic entropy change of 14.6 J/(kg K) and a broad operating temperature window of 18 K under 5 T were simultaneously achieved, correlated with the low thermal hysteresis (∼8 K) and large magnetic-field-induced shift of transformation temperatures (4.9 K/T) that lead to a narrow magnetic hysteresis (1.1 T) and small average magnetic hysteresis loss (48.4 J/kg under 5 T) as well. Furthermore, a large reversible effective refrigeration capacity (76.6 J/kg under 5 T) was obtained, as a result of the large reversible magnetic entropy change, broad operating temperature window, and small magnetic hysteresis loss. The large reversible magnetic entropy change and large reversible effective refrigeration capacity are important for improving the magnetocaloric performance, and the small magnetic hysteresis loss is beneficial to reducing energy dissipation during magnetic field cycle in potential applications.

Development of functionalized carbon nanotube reinforced hydroxyapatite magnetic nanocomposites

An innovative and effective approach is introduced to functionalize multi-walled carbon nanotubes (f-MWCNTs) by in-situ chemical precipitation of hydroxyapatite (HA) to improve their magnetic properties. The HA/f-MWCNTs nanocomposites are obtained by pressureless sintering in vacuum atmosphere. The carboxyl functional group (–COOH) is introduced by an acid treatment on the MWCNT surface. Magnetic hysteresis measurement reveals that HA/f-MWCNTs nanocomposites exhibit excellent hard ferromagnetic properties with saturation magnetization (MS) of 0.233emu/g and coercivity (HC) of 2985.53Oe at room temperature. The maximum magnetic hysteresis loss of 0.44kJ/m3 induces an expected heat generation and it is expected that this nanocomposite has potential to be used as a biomaterial for hyperthermia treatment of bone cancer and other biomedical applications.

Structural, magnetic properties and magnetocaloric effect of Mn1.2Fe0.8P1 − xSixB0.03 compounds

Structural, magnetic, and magnetocaloric properties of the Mn1.2Fe0.8P1−xSixB0.03(x=0.4, 0.5 and 0.55) phases have been investigated. The experimental results show that the critical behavior of the paramagnetic to ferromagnetic phase transition can be tuned through the P/Si ratio. An increase in the Si concentration not only raises the Curie temperature from 176K to 280K, but also changes the nature of the magnetic transition from the first order (for x=0.4) to the second order (for x=0.55) and, thereby, affects the magnetocaloric properties. The peak values of the thermal hysteresis and magnetic entropy change for a magnetic field change of 0–2T are 10K, 4K, 0.8K and −16.3, −8.7, −5.6Jkg−1K−1 for x=0.4, 0.5, and 0.55, respectively. Mechanisms for the magnetic hysteresis loss and possibilities for the room-temperature magnetic refrigeration are discussed.

Magnetic hysteresis loss crossover in Ni0.4Zn0.6Fe1.95Ti0.05O4 ferrite

Ni0.4Zn0.6Fe2O4 and Ni0.4Zn0.6Fe1.95Ti0.05O4 ferrites were prepared by solid state reaction method and their magnetic properties were investigated. It was found that there is a magnetic hysteresis loss crossover around Bm = 4 mT, the hysteresis loss coefficient from 5.5 × 10−2 T−1 in Bm < 4 mT jump down to 4.0 × 10−2 T−1 in Bm > 4 mT in Ni0.4Zn0.6Fe1.95Ti0.05O4 sample by measuring field dependence of relative loss factor. This crossover was verified by measuring field dependence of real part permeability and magnetic loops. The possible mechanism of this crossover was discussed, and it was regarded that the crossover was due to magnetic domain wall pinning by Ti cation doped in ferrite.

Transport ac losses of a second-generation HTS tape with a ferromagnetic substrate and conducting stabilizer

The current–voltage curve and transport ac loss of a second-generation HTS tape with a ferromagnetic NiW substrate and brass stabilizer are measured. It is found that the ac loss is up to two orders of magnitude larger than what is expected by the power-law E(J) determined by the current–voltage curve and increases with increasing frequency. Modeling results show that the overly large ac loss is contributed by the ac loss in the HTS strip enhanced by the NiW substrate and the magnetic hysteresis loss in the substrate, and the frequency-dependent loss occurs in the brass layer covering the substrate but not in the ferromagnetic substrate itself as assumed previously. The ac loss in the brass layer is associated with transport currents but not eddy currents, and it has some features similar to ordinary eddy-current loss with significant differences.

Coupled Magnetic and Structural Transitions in Fe-Doped MnNiSi Compounds

In this paper, we obtained a ferromagnetic (FM) Mn0.36Fe0.6Ni0.98Si compound in which magnetic and structural transitions are coupled together. By combining Fe doping and Mn depletion, the magnetostructural coupling was realized, with a magnetostructural transition happening at 337 K from paramagnetic hexagonal phase to FM orthorhombic phase. The magnetocaloric effect was measured across the transition, showing a wide temperature span and a zero magnetic hysteresis loss. The maximum values of magnetic entropy change and refrigeration capacity near reverse martensitic transition ( $\sim $ 367 K) are −2.52 J kg $^{\mathrm {-1}}~\text{K}^{\mathrm {-1}}$ and 108 J kg $^{\mathrm {-1}}$ , respectively, under a field change of $\Delta H = 0 {\sim }$ 50 kOe.

Effect of Stress on Magnetic Hysteresis Losses in a Switched Reluctance Motor: Application to Stator and Rotor Shrink Fitting

A magnetic hysteresis model is developed based on the vector generalization of Jiles–Atherton (JA) model combined with a simplified multiscale approach to take into account the effect of mechanical stress on the magnetic behavior. The model aims at representing electrical steel behavior under any loading configuration considering the magnetic field vector and the mechanical stress second-order tensor. Mechanical stress is introduced in the JA hysteresis model through the anhysteretic magnetization and a modified pinning parameter. The main properties of the model are shown under alternating and rotating applied induction, especially in terms of hysteresis losses. The differential magnetic susceptibility is derived from the model, and the implementation into a time-stepping finite-element method is detailed. Finally, a quasi-statically rotating switched reluctance motor is studied: considering different shrink-fitting conditions, the resulting stress is shown to have a significant effect on both distribution and global value of hysteresis losses.

Enhanced magnetic refrigeration properties in Mn-rich Ni-Mn-Sn ribbons by optimal annealing.

The influence of annealing time on temperature range of martensitic phase transition (ΔTA-M), thermal hysteresis (ΔThys), magnetic hysteresis loss (ΔMhys), magnetic entropy change (ΔSM) and relative refrigeration capacity (RC) of the Mn-rich Ni43Mn46Sn11 melt spun ribbons have been systematically studied. By optimal annealing, an extremely large ΔSM of 43.2 J.kg−1K−1 and a maximum RC of 221.0 J.kg−1 could be obtained respectively in a field change of 5 T. Both ΔTA-M and ΔThys decreases after annealing, while ΔMhys and ΔSM first dramatically increase to a maximum then degenerates as increase of annealing time. A large effective cooling capacity (RCeff) of 115.4 J.kg−1 was achieved in 60 min annealed ribbons, which increased 75% compared with that unannealed ribbons. The evolution of magnetic properties and magnetocaloric effect has been discussed and proved by atomic ordering degree, microstructure and composition analysis.

Effects of hysteresis and temperature on magnetoelectric effect in giant magnetostrictive/piezoelectric composites

A nonlinear dynamic hysteretic theoretical model on magnetoelectric effect of tri-layered composites is built based on a nonlinear constitutive relation for magnetostrictive material and a linear piezoelectric model for piezoelectric material. And a finite element analysis is implemented to investigate quantitatively the influences of hysteresis and temperature on the ME effect of the layered composites. The model also can explain the “self-biased” response caused by the hysteretic characteristics of the ME composites. Then the distribution of the true displacement along the longitudinal direction is revealed by numerical calculation. The increment of temperature due to the magnetic hysteresis loss is investigated. The temperature, the AC magnetic field and the bias field on the induced electric field and the ME effect are studied, respectively. The results show that the bigger the magnetic frequency, the larger the energy loss of the ME composites. The initial temperature has little effect on the induced electric field at low magnetic field region, but significant effect on the induced electric field at high magnetic field region. The frequency multiplying behavior will disappear when the bias field is strong. In addition, the bias magnetic field also affects the shape of E3∼HAC curve, with the increase of the bias field, the shape of E3∼HAC curve changes from symmetry to asymmetry. The frequency mixing of the induced electric field is also discussed.

Magnetocaloric effect of nonstoichiometric La1−xFe11.4+xSi1.6 alloys with first-order and second-order magnetic transitions

Variation from a first-order magnetoelastic transition (FOMT) to a second-order magnetic transition (SOMT) could be controlled by finely adjusting the Fe/La ratio in the non-stoichiometric La1−xFe11.4+xSi1.6 (x = 0, 0.05, 0.10, 0.15 and 0.20) alloys. Particularly, a nearly stoichiometric ratio of NaZn13-type phase was obtained with an addition of excess 0.15 at% Fe. When x value increased from 0 to 0.20, the Curie temperature (TC) increased from 198.6 to 216.6 K due to lattice shrinkage and the magnetic entropy change (−ΔSM) decreased from 18.4 to 8.0 J/(kg·K) (at 0−2 T) and from 22.5 to 13.8 J/(kg·K) (at 0−5 T), which may be ascribed to the change from the itinerant-electron metamagnetism (IEM) to second order magnetic transition. Thus their effective refrigeration capacities declined from 347.6 to 245.9 J kg−1 under 0–5 T, which values were comparable to the Gd5Si2Ge1.9Fe0.1. The Fe/La ratio in NaZn13-phase was possibly dominant to induce the transition from first to second order among La1−xFe11.4+xSi1.6 alloys. The thermal hysteresis decreased by 87% to 0.3 K and magnetic hysteresis losses reduced by 90% to 1.4 J kg−1 under 0–5 T. Near the transition border, the alloys with x = 0.15 produced a giant magnetocaloric effect of about 11.8 J/(kg·K) under 0–2 T at TC = 205.6 K. The magnetic hysteresis was 3.01 J kg−1 and the thermal hysteresis was 1.9 K. The material near the border of transition could be suitable for future magnetic refrigeration application.

Magnetic properties and magnetocaloric effects in HoPd intermetallic**Project supported by the National Natural Science Foundation of China (Grant Nos. 51322605, 11104337, 51271192, and 11274357) and the Knowledge Innovation Project of the Chinese Academy of Sciences.

A large reversible magnetocaloric effect accompanied by a second order magnetic phase transition from PM to FM is observed in the HoPd compound. Under the magnetic field change of and the refrigerant capacity RC for the compound are evaluated to be 20 J/(kg · K) and 342 J/kg, respectively. In particular, large (11.3 J/(kg · K)) and RC (142 J/kg) are achieved under a low magnetic field change of 0–2 T with no thermal hysteresis and magnetic hysteresis loss. The large reversible magnetocaloric effect (both the large -ΔSM and the high RC) indicates that HoPd is a promising material for magnetic refrigeration at low temperature.

Influence of Mo capping layer on magnetic anisotropy of MgO/CoFeB/Mo

In this paper, the influence of Mo capping layer on magnetic anisotropy of MgO/CoFeB/Mo with varying thickness is studied. It is found that Mo capping layer shows more saturated magnetic moments than Ta capping layer. The direction of the external magnetic field has a great influence on the magnetic anisotropy. The MgO/CoFeB/Mo sample prepared in an applied magnetic field parallel to the plane shows in-plane magnetic anisotropy (IMA). IMA becomes weak as the CoFeB thickness decreases, and it still exists when the thickness decreases to 1.1 nm. At the same time, the saturation field vertical to the plane decreases. When the thickness of CoFeB layer decreases to 0.9 nm or less, the IMA disappears. In our study, the saturated magnetization and magnetic dead layer are 1600 emu/cm3 and 0.26 nm at the annealing temperature 200 ℃, and the interface anisotropy is 0.91 erg/cm2, which is smaller than previous research results. Increasing the annealing temperature helps the sample keep the saturated state under a small magnetic field vertical to the plane, and makes IMA weak and transform into PMA. The variation of the Mo capping layer thickness affects the saturation magnetic moment of the sample. The magnetic moment shows a sharp downtrend when the Mo layer is between 1.2 and 1.6 nm, then it turns stabler with Mo capping layer thickening. Meanwhile, when the Mo capping layer is 1.6 nm, the external vertical saturation field becomes smallest. However under the parallel magnetic field, changing the thickness or annealing temperature, or changing both leads to no PMA occurring. When the magnetic field direction changes from parallel to vertical direction, some of the samples show PMA after the annealing process. The magnetic anisotropy of MgO/CoFeB/Mo varies with the thickness of Mo capping layer. IMA is present when the Mo capping layer is 1 nm or less while PMA is present when the Mo capping layer is between 1.2 and 5 nm. The sample coercive force in the vertical direction varies with thickness, and its magnetic hysteresis loss is much larger when the thickness of Mo capping layer is 1.4 nm.

Martensitic transformation and magnetic features in Ni-Fe-Mn-In Heusler alloy

The Ni50-xFexMn37In13(x=1, 3, 5) polycrystalline samples are prepared by arc melting method. The martensitic transformations and crystal structures for Ni50-xFexMn37In13(x=1, 3, 5) samples are systematically analyzed by measuring the structure and magnetism. The results show that the three samples present different structures at room temperature. In the mean time, with the increase of the content of Fe, the martensitic transformation temperature rapidly decreases, while the ferromagnetism is gradually enhanced for these alloys. Furthermore, both the magnetoresistance and the magnetocaloric effect are also investigated in Fe3 and Fe5 alloys. For an applied magnetic field of 3 T, it is found that the magnetoresistance effects of two samples are about -46% and -15%, while their isothermal entropy changes are about 6 J·kg-1 and 9.5 J·kg-1·K-1 during reverse martensitic transformation, respectively. Accompanied with the disappearing of a very wide transforming range and a slight magnetic hysteresis loss, the net refrigerating capacity of Fe3 sample reaches 96 J·kg-1 in the process of reverse martensitic transformation.

Magnetic properties and large magnetocaloric effect in Laves phase metallic compound

We investigated the magnetic properties and magnetocaloric effect of C15 Laves phase TbMn1.6Fe0.4 by magnetization and heat capacity measurements. A sharp second-order magnetic Tb-Tb ordering transition at Curie temperature TC ~ 120 K and a short-range Fe-Fe ordering transition at ~230 K are observed. Around TC, the compound shows a large magnetocaloric effect with no obvious thermal and magnetic hysteresis loss. The maximum value of magnetic entropy change reaches 8.72 J kg−1 K−1 for a magnetic field change ΔH = 7 T over a wide temperature range. The obtained relative cooling power reaches 184, 560, and 803 J kg−1 for ΔH = 2, 5 and 7 T, respectively. Large reversible magnetocaloric effect and the wide operating temperature range indicate that TbMn1.6Fe0.4 could be a promising candidate for magnetic refrigeration.

Structure, magnetic properties and giant magnetocaloric effect of Tb4Gd1Si2.035Ge1.935Mn0.03 alloy

Tb4Gd1Si2.035Ge1.935Mn0.03 alloy was prepared by arc melting followed by annealing at 1193 K for 168 h. Structural characterizations reveal that monoclinic (Tb, Gd)5Si2Ge2-type phase, secondary phase with orthorhombic 5-4 type structure and hexagonal 5-3 type structure coexist in the alloy. The paramagnetic Curie temperature (θp) is 120 K, indicating that the dominant exchange interaction is ferromagnetic or ferrimagnetic. That the thermal hysteresis of 13 K between heating and cooling and the negative slopes of Arrott plots derived from M–H curves between 116 K and 170 K confirm a typical first-order magnetic transition from ferromagnetism to paramagnetism occurs. The maximum magnetic entropy changes of the Tb4Gd1Si2.05Ge1.95Mn0.03 alloy for magnetic field changes of 0–1 T, 0–2 T, 0–3 T, 0–4 T and 0–5 T are about 3.3, 8.6, 14.0, 18.9 and 22.4 J/kg K, respectively. And the effective refrigeration capacity (RCeff) value is 231 J/kg with a subtracted magnetic hysteresis loss of 30 J/kg for a magnetic field change from 0 to 5 T. Large −ΔSM and RCeff suggest that Tb4Gd1Si2.035Ge1.935Mn0.03 alloy is an attractive potential magnetocaloric material working in the vicinity of 143 K.