Evaluation of Relaxational and Hysteretic Heat Losses in Concentrated Magnetic Fluid under Influence of Alternating Magnetic Field

This article describes the magnetic and hyperthermic investigation of a concentrated magnetic fluid on the basis of a transformer mineral oil with magnetite particles. The structure of a ferrofluid and general magnetic parameters of a medium were determined from vibrating sample magnetometer measurements. The hyperthermic experiments were carried out at a frequency f = 1500 kHz for various magnetic field amplitudes. The analysis of calorimetric results allowed an estimate of the contribution of relaxational and hysteresis loss mechanisms in total energy losses in the hyperthermic effect under the influence of an alternating magnetic field. Additional calorimetric measurements were also performed (at H _C = 1500 A · m⁻¹) versus frequency in the range from 50 kHz to 2 MHz which indicated that for f _o =  653 kHz the heating process is the most effective.     

Influence of Critical Current Density Distribution on Transport AC Losses in Superconducting Wire in a DC Magnetic Field

In typical application-like conditions, the inhomogeneous distribution and anisotropy of critical current density must be considered simultaneously in transport AC loss calculation. In this paper, we derive the analytical formulas of transport AC losses for high-temperature superconductors (HTSs) with linear and quadratic distribution of critical current density under applied DC magnetic field. The influence of the inhomogeneous distribution and anisotropy of critical current density has been analyzed. The results show that the impact of the distribution form on transport AC loss is more obvious under applied DC magnetic field. And the influence of applied DC magnetic field will increase as the distribution form becomes steeper.     

Study of Specific Heat of Quantum Pseudodot Under Magnetic Field

In the present work, the specific heat of a GaAs quantum pseudodot in the presence of an applied magnetic field is studied. For this purpose, the Tsallis formalism is applied to obtain the specific heat. It is found that the specific heat is a continuous function and it is zero at special temperatures. The specific heat decreases with increasing temperature. There are several peaks in the specific heat and these are dependent on the quantum radius and magnetic field.     

Domain Wall Dynamics in Thin Magnetic Wires Under the Influence of Transversal Magnetic Field

We have studied the domain wall dynamics in thin amorphous glass-coating microwires under the influence of both axial and transversal magnetic fields. Two different regions of domain wall dynamics have been found according to the amplitude of the applied magnetic field rotated out of the wire's axis. At low amplitude, the effect of applied field rotation is reduced to the reduction of its axial component and the domain wall velocity decreases. For high amplitudes of magnetic field, the maximum velocity was found when applied field forms angle ${-}20^{circ}$ with the wire's axis. The results are explained in terms of different domain wall structure, being transversal for low amplitudes of magnetic field and vortex for high amplitude of applied magnetic fields.      

Angular Dependence of Transport AC Losses in Superconducting Wire with Position-Dependent Critical Current Density in a DC Magnetic Field

Transport AC losses play a very important role in high temperature superconductors (HTSs), which usually carry AC transport current under applied magnetic field in typical application-like conditions. In this paper, we propose the analytical formula for transport AC losses in HTS wire by considering critical current density of both inhomogeneous and anisotropic field dependent. The angular dependence of critical current density is described by effective mass theory, and the HTS wire has inhomogeneous distribution cross-section of critical current density. We calculate the angular dependence of normalized AC losses under different DC applied magnetic fields. The numerical results of this formula agree well with the experiment data and are better than the results of Norris formula. This analytical formula can explain the deviation of experimental transport current losses from the Norris formula and apply to calculate transport AC losses in realistic practical condition.     

Influence of Magnetic Field Amplitude on Quantity and Sizes of Disintegration Fragments of Magnetic Particles Cluster

The disintegration of a mass of magnetic particles is investigated at pulsing switching on a magnetic field. The influence of field value on quantity, sizes and allocation of fragments of disintegration is explored. The presence of two critical fields, defining the process of disintegration, is revealed. The results can be used at manufacture of packings to magnetic filters.     

Experimental Evaluation of AC Losses in the Cold Dielectric High-Temperature Superconducting Cable

The alternating-current (AC) losses in the 20-cm Bi-2223/Ag tape cold dielectric high-temperature superconducting (CD HTS) test cable are experimentally evaluated. The method used is the electrical method which is based on a lock-in amplifier. Firstly, the AC losses of the CD HTS cable which has two conductor layers and one shield layer are measured. Then, in order to eliminate the error caused by joint resistance, a test is designed to measure the joint resistance of each layer. The measured losses that eliminated the error due to joint resistance are found to be in good agreement with calculated ones with the monoblock model, Carr, and Magnusson equations at the frequencies of 50 ～ 300 Hz. Finally, the errors caused by joint resistance and other uncertain factors are discussed.     

Relaxation Losses of Magnetic Excitations in Nanoscale Films of Yttrium Iron Garnet

Relaxation losses of magnetic excitations in nanoscale films of Y₃Fe₅O₁₂ (YIG) were studied. The films were obtained by laser molecular-beam epitaxy (LMBE). Ferromagnetic resonance linewidth ΔH was found to increase sharply as the temperature decreased from 300 to 77 K. The observed growth of ΔH is explained by typical relaxation processes caused by the presence of Fe²⁺ ions. This effect is not observed in thick films of YIG grown by liquid-phase epitaxy and containing Pb⁴⁺ ions, and, hence, we have concluded that the presence of acceptor ions in YIG films obtained by LMBE will facilitate decreasing the concentration of Fe²⁺ ions and, a result, diminishing relaxation losses.     

Effect of Iron Particles Size on the High-Frequency Magnetic Properties of Iron-Borosilicate Soft Magnetic Composites

Iron-borosilicate magnetic composites could be applied as a soft magnetic material in high temperature and high frequency applications. In this research, the magnetic properties of soft magnetic composites with different iron particle sizes made by spark plasma sintering have been investigated. Different magnetic properties such as permeability, loss factor, and quality factor were examined up to frequencies in the order of kilohertz. The microstructural observations indicated the distribution of borosilicate on the iron grain boundaries. The results revealed that the loss factor is smaller for composites with fine particles at high frequencies. In addition, the magnetic impedance for smaller particles was greater. It was also found that the permeability and quality factor of composites with coarse particles are larger than those of fine particles. Indeed, when the particles become coarse, the density of porosities and consequently, the demagnetizing fields decrease which result in the increase of permeability. Furthermore, when the size of particles reduces, the density of grain boundaries enhances which is the main reason of lower loss factor achieved in the composites with fine particles.     

Influence of AC External Magnetic Field on the Levitation Force Relaxation of HTS Bulk Above NdFeB Guideway

In the present High-Temperature Superconducting (HTS) maglev vehicle system, the air gaps between the adjacent permanent magnets make the magnetic fields above the NdFeB guideway non-uniform. So one is required to study the characteristics of levitation force of the HTS bulk influenced by non-uniform fields. In this paper, we have studied the characteristics of the levitation force relaxation by an experiment in which the AC external magnetic field generated by an electromagnet is used to simulate the time-varying external magnetic field caused by the inhomogeneity of the NdFeB guideway. From the experiment results, it is found that the levitation force is attenuated with the application of the AC external magnetic field, and the decay is increased with the amplitude of the AC magnetic field, but the decay is almost independent of the frequency of the AC magnetic field.     

磁镜场约束中粒子运动的数值计算

由单粒子轨道理论,从分析磁镜场中荷电粒子的受力情况出发,应用计算机数值求解方法模拟了磁镜场中荷电粒子的运动情况.结果表明:与经典的理论分析结果不同,当荷电粒子的起始位置与磁轴的距离不等于其拉摩尔半径时,荷电粒子在平行磁轴方向和垂直磁轴平面中的速度分量存在着周期性变化,其周期为荷电粒子的拉摩尔周期;同时其损失锥的临界角随着荷电粒子起始位置与磁轴的距离的增大而略有减小.     

The Numerical Study of Influence of Flux Creep on AC Losses in Superconductors

Numerical simulation of AC losses in superconductors with gaint flux creep was carried out based on the collective creep model of the vortex glass. Influence of physical parameters, including frequency (f) and the amplitude (B _ac) of AC field, current density distribution (j), DC field (B _d), and temperature (T) on AC losses was studied based on a unified method and the Maxwell equations. The frequency-dependent AC losses is the most important among the results which differ from the static models. Also, AC losses derived in the flux creep state are larger than those in the critical-state when the sample is only partly penetrated by the field, which is the second difference between the flux creep model and the static models. Moreover, the dependence of AC losses on B _ac are derived and compared with that based on the Bean model. Preliminary comparison with experiments showed that the procedure could give qualitative understanding and estimation of AC losses in superconductors with giant flux creep.     

Magnetic Field Influence on the Low Temperature Heat Capacity and Heat Release of (TMTSF)2PF6

We have measured under applied magnetic field the heat capacity c _p and heat release of the quasi-1D conductor (TMTSF)₂PF₆ in its spin density wave (SDW) ground state. The low-temperature heat capacity (T < 0.5 K) is dominated by a Schottky anomaly contribution. A corresponding term was also found for the heat release. In this T-range both properties are strongly sensitive to moderate magnetic fields (i.e., below 0.5 T): their amplitudes have a sharp maximum for H _c=0.2 T. We show that the corresponding density of two-level states N _S undergoes a sharp maximum at H _c, which rules out an extrinsic origin for the two-level states. Instead we suppose an intrinsic origin, such as defects of commensurability of the SDW, as the (slow) excitations related to the domain walls. This effect is found to be independent on the field orientations H a and H a.     

Transport and Magnetic AC Losses in Ag/Tl-1223 Tape and the Effect of Mechanical Damage

In this paper we present the results of AC loss measurements on silver clad monocore tapes of Tl-1223 prepared by the powder-in-tube method. Losses arising from an external AC magnetic field are compared with those generated by AC transport currents (self-field losses). Critical current densities are derived from magnetic loss data and compared with those measured by the four point transport method. It was found that mechanically induced stresses (introduced by bending) only have a significant effect on the transport losses, via the critical current degradation. Such changes are not seen in measured magnetic losses, which are independent of mechanical stress, and remain unchanged, at least in the stress range used in our experiment.     

Scientific Research in the Field of Mesh Method Based Modeling of AC Losses in Superconductors: A Review

As in all research in engineering sciences, the final target in the research of superconductor technology is the construction of new and innovative applications—hopefully with commercial potential. Mesh method based modeling of AC losses in superconductors is an important field of engineering science when considering the commercialization of superconductivity, as AC losses can often be a restricting factor for the feasibility of superconducting AC applications, and thus, analyzing them beforehand is necessary. Hence, it is important that new results and ideas in this field are widely recognized and acknowledged both in scientific and industrial circles. To achieve a wider impact, a clear classification of the research is beneficial. In this topical review, we discuss the possibilities in this field by presenting a classification of research into seven different research directions. We emphasize the roles of these different types of research as connections between steps on the path from theory to applications. Furthermore, we present a review of recent research in these research directions.     

Numerical Evaluation of Levitation Force Oscillation of HTS Bulk Exposed to AC Magnetic Field over NdFeB Guideway

The levitation force of the YBCO bulk over an NdFeB guideway used in the high-temperature superconducting (HTS) maglev vehicle system is oscillated by the application of the AC external magnetic field. In our previous work, we interpreted that the oscillation is due to the shielding current fluctuation caused by fluctuant external magnetic field. In this paper, based on the Bean model, an analytical model is adopted to evaluate the levitation force. Comparing with the experimental results, the calculated results show good matching. The model can reveal the oscillation characteristics of the levitation force of HTS bulk which is being exposed to AC external magnetic field. Therefore, the levitation force oscillation of the HTS bulk in the maglev vehicle system can be evaluated by this numerical method.     

General Properties of Low-frequency Power Losses in. Fe-based Nanocrystalline Soft Magnetic Alloys

1. IotroductlonAs early as 1969, it was reported that the dynamicloss at 50 Hi in the high-grade grain-oriented 3%SiFereaches about 75% of the practical measured total lossP and is much larger than the so--called classical eddycurrent loss Pc,l']; It was also observed that the total loss per cycle p/f nonlinearly increases with increasing frequency f in the low frequency range notmore than 100 Hi[1]. The above mentioned nonlineardependences have early been observed in many crystalline and am…     

影响磁性氧化铁纳米颗粒磁热疗加热效率的因素

磁性纳米颗粒作为产热介质在生物医学方面取得了广泛的应用前景.近年来,新开发的纳米颗粒细胞内疗法更是克服了常规治疗方法的副作用,使治疗效率大大提高.氧化铁纳米颗粒由于其优异的磁性能在磁热疗应用的磁性纳米颗粒中脱颖而出,但存在着在交变磁场下加热效率受限的问题.具有高加热效率受限的磁性纳米粒子是磁热疗的必要条件.本文综述了近...     

An Evaluation of the Three-Voltmeter Method for AC Power Measurement

The accuracy and frequency response limitations in the present square-law responding laboratory wattmeters have promoted the search for alternate methods of ac power measurement using electronic instrumentation. The three-voltmeter method is based on an old principle of operation implemented by new analog circuitry. Results of the tests reported here show a precision of power calculation with 0.01 percent error at frequencies below 5 kHz. A unique test procedure is described for the comparison of the three-voltmeter device and a time-division multiplier wattmeter operating at zero power factor.