We carried out investigation on the magnetic properties of MnAs thin film grown on GaAs(001) substrate by using molecular-beam epitaxy. The magnetic Curie temperature was ~340 K which was higher than that of the bulk. Magnetization (M) versus magnetic field (H) showed strong two-fold symmetric anisotropy. At low temperature of 2 K, the M-H curve and temperature dependence of magnetization exhibit peculiar behavior that has not been observed before. It should be noted that these unique results were only observed when a magnetic field was applied. We also observed a weak-localization-like magnetoresistance (MR) at 2 K. As an origin of the observed peculiar magnetic properties and MR, we suggest diamagnetic domains which are phase transited from ferromagnetism at low temperature.

The prime intention of present article is to study the behavior of magnetized Williamson nanofluid. Flow governing model is obtained considering flow over variable thickness surface with convective heat and mass boundary constraints. The effects of Joule heating, Brownian diffusion and thermophoresis are further considered. Moreover, chemical reaction associated with activation energy is accounted. Boundary layer assumptions are used to obtain the dimensional system of differential equations. The system of PDE's are converted into ODE’s ones using transformations. Magneto fluids are relatively prevalent in liquid metals, salt water, plasma, metallurgy, cancer therapy and drug delivery target. The considered investigation has relevance in metallurgical processes, polymer industry and plastic sheet. The governing model of ODE’s is then tackled via HAM for convergent series solution. Influence of pertinent variables on velocity, concentration, temperature, total entropy rate, skin friction coefficient, Bejan number, local heat and mass transfer rates are studied graphically. Main outcomes are enlisted at the end.

In modern cities, consideration must be given to both the development of electric energy and the improvement of landscape. Therefore, power technicians usually substitute underground cables for overhead lines. Moreover, junction towers are always employed to provide this interface between overhead lines and underground cables. This study focuses on reducing eddy current losses of a power junction tower. The losses in structural steels of a tower will be computed, and different cable arrangements are discussed by finite element method. Furthermore, the results indicate that eddy current losses of steels can be reduced by performing cable sequencing and reconfiguration without any new facilities. The reduction scheme can be useful for reducing eddy current losses of junction towers.

We present theoretical study on spin reorientation transition (SRT). A phenomenological model is provided, which treats magnetic energy as sum of magnetoelasticity, magnetocrystalline anisotropy, and demagnetization contributions. We show that critical strain exists by analytically solving the phenomenological model, as a consequence of an interplay between aforementioned contributions. For more quantitative understanding, numerical estimate is performed for thin FePt and Fe₆₀Co₄₀ films, where experimentally accessible critical strain is 2 %. Further, this feasible strain is due to the large magnetoelastic coefficient (b₁) and the optimal saturation magnetization, which is not achievable in thin Fe film.

This paper proposes a design of 90 kW concentrated flux synchronous motor (CFSM). A ferrite magnet is used because of low price compared to rare-earth materials and this spoke type structure of motor can be an alternative to the interior permanent magnet synchronous motor (IPMSM) using NdFeB. However, a greater size of ferrite magnet is required to achieve the same torque as NdFeB is used, because the residual induction of ferrite is approximately one third of NdFeB. Consequently, the spoke type structure is applied to improve the torque density. In the design process, methods of deciding the stack length, stator diameter, rotor diameter, and the number of poles and slots are suggested. Series turns per phase are determined by applying back-electromotive force-inductance map (EL map) in the initial design. A response surface method is applied for the optimization. Furthermore, a structural analysis is also conducted to confirm the safety at high speed. Finally, test of CFSM is conducted for the verification.

Here hydromagnetic flow of an incompressible Dary-Forchheimer fluid over a curved stretching surface is addressed. Heat source/sink and dissipation effects are considered in heat equation. Entropy generation is discussed through thermodynamics law. Bejan number is calculated. The proposed system are modeled in curvilinear coordinates. Partial differential system are reduced to ordinary one through transformation. ND-solve method is implemented to solve the given system. Graphical outcomes of velocity, entropy rate, temperature and Bejan number against flow variables are discussed. Numerical outcomes of drag force against pertinent variables are examined through table. Higher Hartman number decreases velocity field. A reverse effect for velocity is observed through porosity and curvature variables. An improvement in temperature is seen for curvature variable. An augmentation in entropy rate is noted for Brinkman number.

BLDC motor has the high efficiency, high power density, low acoustic noise, and low maintenance cost due to the removal of the mechanical commutators and brushes. In the general design and driving control technology about BLDC motor, the square waveform phase current has been known as the ideal current waveform to get high torque production and high efficiency driving characteristics. But in here, the kinematic vector characteristics of magnetic force between stator and rotor pole is not considered. Conventionally recommended square wave current has no consideration about this vector angular feature of magnetic force. This paper studied about this vector potential separation of magnetic force during torque production to generate maximum torque per ampere (MTPA). The modified current waveform for MTPA is suggested by this study. In addition, this paper also suggests 2-step voltage control method for MTPA and high efficiency driving. The optimal voltage control condition is derived by DOE (Design of Experiments) and RS (Response Surface). This suggested control method is validified by finite element analysis (FEA) using voltage source operation to simulate real driving condition. As a result, the suggested control method can be a good driving control technology to maximize the output torque per ampere and improve the driving efficiency.

The melt-spinning method combined with annealing technology was used to prepare Mn-based permanent alloys in the paper. The influences of Fe-doping on the microstructure and magnetic performances of the MnBi alloys were studied. According to the results of XRD pattern, the fraction of the LTP-MnBi in the as spun MnBi ribbons increases with the doping of Fe element, a significant increase of the LTP-MnBi is due to annealing treatment. The magnetization at the 20 kOe field of Mn₅₅Bi₄₀Fe₅ melt-spun ribbons increases to 45 emu/g after being annealing. With the addition of Fe, the coercivity H_cj of the annealed ribbons increases first and then decreases. The results of δM plots show that the reduction of H_cj for the Mn₅₅Bi₄₀Fe₅ melt-spun ribbons can be attributed to enhanced exchange coupling interaction between MnBi LTP particles. The grain refinement contributes directly to an enhanced exchange coupling for the addition of 5 at% Fe from TEM images. The dependence of coercivity on temperature for the annealed MnBi alloy melt-spun ribbons is discussed.

The mischmetal-based sintered magnets were prepared by mixing MM_8.8Nd_3.4Fe_81.8B₆ (MM denotes mischmetal) with Nd₁₅Fe₇₉B₆ alloys. The magnet consist of two main phases i.e., (La,Ce)-rich main phase and Nd-rich main phase. For the mass ratio of 8:2 of MM_8.8Nd_3.4Fe_81.8B₆ and Nd₁₅Fe₇₉B₆, many grains of La-Ce-rich main phase are interconnected and the effect of enhancing the coercivity is weak in the sintered magnets. While for the mass ratio of 6:4 most grains of (La,Ce)-rich main phase are nearly separated and covered by the Nd-rich main phase and intergranular phase, and the coercivity increases significantly to 7.70 kOe. Compared with (MM_0.3Nd_0.7)_30.3Fe_balB_0.96Cu_0.1Al_0.11 magnets prepared by the conventional method, the coercivity doesn’t decrease in the sintered composite magnets of MM_8.8Nd_3.4Fe_81.8B₆/Nd₁₅Fe₇₉B₆ though the MM content of 40 wt.% is higher. The optimization of Nd-rich-main-phase distribution as well as Nd substitution for La-Ce should be responsible for the significant increase of coercivity.

We report the polyvinylpyrrolidone (PVP) encapsulated MnZn ferrite (Mn_0.8Zn_0.2Fe₂O₄/PVP) nanocomposite for low-temperature magnetic properties prepared by the facile one-pot sol-gel route. The transmission electron microscopy analysis revealed spherical shape ferrite particles in a polymer matrix (Mn_0.8Zn_0.2Fe₂O₄/PVP nanocomposite) with an average particle size of 11.6 nm. The Rietveld refinement of X-ray diffraction (XRD) data revealed the pure cubic spinel structure formation. The lattice parameter is 8.3825 Å, and the average crystallite size is 10 nm evaluated from XRD data. Raman spectroscopy analysis is in agreement with XRD results. The temperature-dependent magnetization analysis disclosed the effective anisotropy constant K_eff, the value of 3.0 × 10⁴ J/m³. The meticulous investigation of magnetic field-dependent magnetic properties from 2 K to 350 K unveiled superparamagnetic (SPM) behavior. From the electron spin resonance (ESR) analysis, the calculated g value and spin-spin relaxation time (T₂) are 2.03 and 2.52 × 10^-11 sec, respectively, which confirms the SPM behavior.

Measuring the vector magnetic properties of nanocrystalline soft magnetic materials at high frequencies is of great significance to the optimal design and energy saving of the electrical equipment. In this paper, some key design issues are discussed for a rotational single sheet tester (RSST) to further studied the Two-Dimensional (2D) magnetic properties of nanocrystalline alloys in the kilohertz range. Firstly, the magnetization uniformity of the testing sample is analyzed and discussed considering the stray field. Secondly, the magnetizer's geometric dimensions are optimized to achieve higher magnetic flux density levels with the minimum energy consummation. Thirdly, the magnetic field and the magnetic flux density sensing system are optimally designed to measure the nanocrystalline alloys' magnetic properties at high frequencies. Finally, a robust controlling algorithm is developed to control the magnetic flux density waveform to sinusoidal in the x and the y-direction. Obtained results show that the proposed structure can measure the vector magnetic properties of nanocrystalline alloys up to 10 kHz.

The compositions of Co substituted Ni-Zn ferrites having the formula Ni_0.65-xCo_xZn_0.35Fe₂O₄ (where x = 0.00, 0.01, 0.03, 0.05, 0.07 and 0.09) were prepared by the solid state reaction method and sintered at 1350 ℃. The structural property was observed with X-ray diffraction (XRD) method and it showed the single phase cubic spinel structure. Saturation magnetization (M_s), experimental magnetic moment (n_exp) and coercive field (H_c) have been investigated. It was observed that the larger value of M_s was found at x = 0.03 due to its stronger super-exchange interaction between two sub-lattices in the spinel ferrites. However, M_s decreases for 0.05 ≤ x ≤ 0.09 due to the effect of Yafet-Kittle angle. All the compositions are found to be smaller value of H_c, which indicates the magnetic softness nature of the spinel ferrites. The initial permeabilities were increased which could be attributed to the densification of the samples.

This paper deals with a permanent magnet synchronous generator (PMSG) for diesel engine generators. Generally, a silicon steel sheet is used to minimize eddy current losses of the stator and rotor cores of a generator. However when a silicon steel sheet is employed to produce the core of the stator and rotor, manufacturing costs increase due to the high cost of the silicon steel sheet. To reduce these costs, a 5 mm SSC400 rolled steel can be used as an alternative to the silicon steel sheet. However, the SS400 rolled steel with a thickness of 5 mm can increase the eddy current losses of the core. In this paper, in order to overcome this problem, a slit type rotor core is employed. In this case, eddy current losses can be reduced, resulting in improved THD (Total Harmonics Distortion) of the induced EMF (Electro-Motive Force). The eddy current losses and THD of the induced EMF according to the number of slits is also analyzed. Moreover, a prototype is produced for the final model, and the effectiveness is confirmed through experiments.

In order to improve the pressure capability of reciprocating sealing structure with magnetic fluid, the L₁₆(4⁵) orthogonal test design and the numerical simulation with the finite element method. were combined to optimize the sealing structure. In the process of orthogonal test design, five factors, four levels and the corresponding orthogonal table were selected. The magnetic field distribution of each orthogonal test was calculated and analyzed by finite element method. The results of orthogonal test were statistically analyzed by using range analysis and variance analysis and it shows that the simulation result of pressure capability of the optimal scheme is the best result in the test simulation analysis. The results showed that the pressure capability of the optimal scheme is about 0.91 MPa higher than that of the initial reciprocating seal with magnetic fluid.