These authors contributed equally to this work

0.67BiFeO₃-0.33BaTiO₃-xwt%Mn ceramics were synthesized using the SPS method. Fine BiFeO₃-BaTiO₃ ceramics with a morphotropic phase boundary were formed, as demonstrated by XRD and SEM. The dielectric constants reached approximately 4000. The ferroelectric properties of Mn-doped BiFeO₃-BaTiO₃ were significantly improved compared with undoped BiFeO₃-BaTiO₃. The highest magnetic properties were obtained when the sintering temperature was 820 ℃ and the doping content was 0.3 wt%, and were superior to those fabricated using other methods. The Mn-doped BiFeO₃-BaTiO₃ multiferroic ceramic synthesized in this work shows promise for application in data storage.

In this study, the harmonic orders of varying magnetic flux density with respect to slot combinations are scrutinized through a spatial and temporal fast Fourier transform. A three-phase four-pole induction motor is selected, and, as its base model, 36 and 28 slots are set up in the stator and rotor, respectively. Eleven models with different numbers of rotor slots were designed to study torque ripples with respect to slot combinations. The correlation between torque ripple and slot harmonics in a stator and rotor is described thoroughly by comparing the tangential and radial magnetic flux densities in the air gap, tangential force density, and harmonic orders in torque. Some models having deteriorated torque ripples have one or more slot harmonic orders in common in the stator and rotor. The other models exhibit the same commonalities, but a small torque ripple occurs because of the high harmonic orders. Models with 24 stator slots are investigated through the same procedure to generalize the relationship between torque ripple and slot harmonics in 36 stator slots.

A simple and improved analytical model (AM) for linear permanent magnet synchronous machine (LPMSM) based on the correction factor is presented in this paper. A slotless linear permanent magnet machine (PLPM) with AM developed in Cartesian coordinate is selected to investigate. Consequently, the fitting equations of curvature factors for the permanent magnet and armature are obtained. The subdomains for LPMSM are simplified from 6 down to 3 domains based on curvature equations. The magnetic flux density and force show that the proposed approach agrees with the finite element (FE) model. Moreover, the reduced calculation domains and harmonic orders make AM proposed in the paper much faster. The main contribution of the work is to present a simple strategy for coordinate transformation and calculation strategy for LPMSM, which provides guideline for designers to investigate the machines developed in Cartesian coordinate.

Electric field dependence of magnetic, electronic, and structural properties in a Pd bilayer film on MgO (001) is investigated by using the first-principles electronic structure calculations within density functional theory. We find that, due to the lattice mismatch of 6.7 %, a ferromagnetic ground state is stabilized at zero electric field on an otherwise paramagnetic Pd with the spin magnetic moments of m = 0.31 and 0.34 μ_B in surface and interface Pd, respectively. The application of an external electric field, E, causes the Pd magnetic moments to be modulated in a site- and electric field-dependent manner. As the external electric field pointing inward to the Pd surface is increased up to the critical value of 1.3 V/Å, the surface Pd moment is barely changed while the interfacial Pd moment increases linearly with E. Above this critical electric field, the moments of both the interfacial and surface Pd atoms exhibit nonlinear increase with E and reach up to 0.34 (surface) and 0.41 (interface) μ_B at E = 2.5 V/Å. When the electric field direction is inverted, a similar dependence on E is obtained for both Pd atoms at the critical electric field value of -0.5 V/Å. The peculiar behavior of the induced magnetic moments is explained by combining the linearized Stoner and itinerant conduction models. We reveal that this prominent magnetoelectric effect is due to the modulated charge occupancy of Pd 4d-states in the minority spin channel in which the d_z² and d_x²-y² orbitals play crucial roles.

This study proposes an analytical approach by optimum process that is generalized by number of phases, magnet, and pole-pair of linear machines based on a physical magnetic circuit model. The linear machine increases the force output of the machine due to generation of the magnetic field created by the armature winding. There is a strong attractive force between the iron-core armature and the permanent magnet. Therefore, this paper deals not only with one-phase systems by the number of magnet and pole pairs but also two-phase machines in linear machines. All this is carried out for optimum process using geometric parameters based on analytical electromagnetic field research. The best structure for optimum design is selected by a parameter study and it is accomplished with 2-D finite element analysis. The object function and design variables for this parameter study by constraints are chosen for practical and effective design of the machine. Eventually, it suggests new design rules based on optimal design through parameter study. The proposed methods allow us to draw a very important design rule, as a result it can be provided to less time of the machine design and analysis.

The power transmission of magnetic gears, based upon the at-tractive force of magnets, does not involve direct contact between the power transmission shafts. Thus, vibration or noise, due to friction, can be reduced. However, magnets and iron cores, which are the main components of magnetic gears, generate cogging torque. This increases torque ripples that are the cause of the noise and vibration of permanent-magnet (PM) machines. In this study, a torque ripple reduction method, using the combination of number of poles and number of pole pieces was proposed. This method uses the structural characteristics of magnetic gears only. This method was suggested instead of the existing torque ripple reduction methods for PM machines to reduce the torque ripples of magnetic gears. Furthermore, the correlation between the numbers of poles, pole pieces, and torque ripples was analyzed. From this analysis, a design guideline that minimizes torque ripples in the initial design of magnetic gears was proposed.

Magnetic fluid seal is one of the most mature applications of magnetic fluid. When the shaft has a large radial runout, the classical pole piece is easily damaged. Due to its small size, the commonly used pole piece structure harbors problems like poor seal performance under a large gap and poor processability. By exploring the distribution law of the magnetic field on the magnet’s surface, we provided theoretical support for the magnetic fluid seal using axially-magnetized ring magnets. New structures for the magnetic fluid seal using axially-magnetized slotted ring magnets and the magnetic fluid seal using radially-magnetized ring magnets were proposed. Then, comparisons were made between the classical magnetic fluid seal and the magnetic fluid seal using ring magnets. The results revealed that the magnetic fluid seal using axially-magnetized slotted ring magnets and the magnetic fluid seal using radially-magnetized ring magnets exhibited a certain seal capacity, which could replace the classical magnetic fluid seal structure.

In this research, we study four influence factors of the damping performance of ferrofluid dynamic vibration absorber, as well as predict and optimize the damping performance by machine learning method. The vibration absorber in our research is based on the second order buoyancy principle, which consists of a non-magnetic container, a small amount of ferrofluid and a permanent magnet. The effects of the initial amplitude, the cone angle of the cover, the thickness of the gasket and the mass of the ferrofluid on the damping performance are investigated by experiments. Based on the experiment data, we use BP neural network to establish a prediction model between the four influence factors and the damping performance. The prediction error of damping efficiency predicted by BP neural network is mainly within ± 0.4%. Meanwhile, the determination coefficient R2 of test data is 0.96242. The both indicate that BP neural network has a good performance in predicting the damping efficiency. Furthermore, we use the search algorithm to find the optimized values of each influence factor through the prediction model and the high damping efficiency is confirmed by experiments. Our work introduces machine learning into the field of vibration absorber designing, which provides an innovative method for the rapid design of high efficiency vibration absorber.

In order to solve the problem of poor sealing performance of rotating machinery under the condition of small clearance, a new type of divergent magnetic fluid seal device with small clearance and double magnetic source is designed in this paper. The effect of magnetic fluid injection, tooth number and sealing clearance on the sealing pressure resistance of dual magnetic source divergence were studied and compared with the experimental value of ordinary magnetic fluid seal. The experiment results show that the pressure resistance ability of divergent magnetic fluid seal is at least 3 times that of ordinary magnetic fluid seal, which verifies the correctness of divergent magnetic seal with small clearance and double magnetic source pressure resistance theory, and has important theoretical guiding significance for solving the problem of poor magnetic fluid seal performance under small clearance.

Considering various unstable factors when the large-diameter spindle operates at a high speed, such as eccentricity, centrifugal force, etc., the ordinary ferrofluid seal structures will show poor sealing performance. This paper proposes an axial-radial bidirectional ferrofluid seal structure with radial oblique teeth to improve the sealing performance. The pressure resistance of the radial ferrofluid seal structure in the magnetic circuit is theoretically analyzed. The magnetic flux distribution characteristic in the gap of the oblique teeth is studied by magnetic field simulation. According to the analysis results of the magnetic induction intensity, to obtain the larger theoretical pressure resistance, the optimal angle of oblique teeth is 77.87°, 64.28° and 62.81° under the radial seal structure with different gaps of 0.1 mm, 0.15 mm and 0.2 mm, respectively. In addition, simulation analysis is carried out to obtain the fluid pressure and velocity distribution of the radial ferrofluid seal structure with different oblique teeth angles. When the oblique teeth angle is small, the pressure drops and gas flow speeds in the ferrofluid area are all lower, and the pressure resistance is higher.

We prepared and characterized nickel-substituted cobalt ferrite (Ni_0.1Co_0.9Fe₂O₄) nanoparticles using the sol-gel method. The physical properties of the nanoparticles have been modified by postannealing treatment at atmospheric conditions. X-ray diffraction results confirmed that the nanoparticles possessed a single-phase face-centered cubic crystalline structure. The crystallite sizes increased from 20.85 to 26.06 nm with the increased annealing temperature. Transmission electron microscopy results confirmed the crystal structure of the nickel-substituted cobalt ferrite nanoparticles. Furthermore, Fourier-transform infrared spectroscopy results showed that the typical characteristic absorption of the nanoparticles was obtained at wave numbers k = 575 and 374 cm⁻¹. Finally, the saturation magnetization and coercivity of the nanoparticles increased with the annealing temperature, which is attributed to the increase in magnetic anisotropy constant.

Structural and magnetic properties of ScFeO₃ compound were investigated by X-ray diffraction (XRD), X-ray photoelectron spectroscopy, and vibrating sample magnetometry (VSM) in comparison with those of Fe₂O₃ and Sc₂O₃. The specimens were prepared as thin films under identical sol-gel deposition process. The XRD data indicated that the ScFeO₃ specimen have cubic bixbyite structure, identical to that of the Sc₂O₃ specimen but different from that of the Fe₂O₃ specimen (rhombohedral). The estimated lattice constant of ScFeO₃ is smaller than that of Sc₂O₃ by 2.9 %. According to the VSM data, the ScFeO₃ specimen showed a magnetic hysteresis curve that is alike in shape to that of the Fe₂O₃ specimen with the saturation magnetization of the former (2.6 emu/cm³) being smaller by 30 % than that of the latter (3.7 emu/cm³). The observed small magnetization in ScFeO₃ implies an antiferromagnetic spin alignment of neighboring Fe³⁺ ions with canted spin magnetic moment.

The magnetic flux leakage (MFL) type non-destructive inspection can be performed only when the metal object is sufficiently magnetically saturated. Therefore, since the general MFL sensor system used for pipeline inspection must sufficiently saturate the pipe, the weight and size of MFL sensor system are inevitably increased according to the diameter or thickness of the pipe. However, if the weight of the MFL sensor system is excessively increased, it is difficult to drive, and thus it is difficult to inspect a pipe having a large diameter. In this paper, the novel MFL sensor system which can be inspected large-diameter pipes without increasing the weight of the MFL sensor system is proposed and compared to the conventional MFL sensor system used for the pipe inspection. Since the proposed MFL sensor system is a system that saturates the pipe locally, it has the advantage of being able to inspect the pipe regardless of the pipe diameter.

The numerical solution of the flow non-Newtonian fluid induced by stretching sheet in the region of oblique stagnation point flow under inducement of externally applied uniform magnetic field orthogonal to the flow is presented. The analysis is made under the assumption of boundary layer which arrives to the system of partial differential equations which are then transformed to ordinary differential equations by using appropriate similarity transformations. The numerical solution of the modeled system of equation is obtained by parallel shooting technique and presented for different variations of involved parameters. It is noted that enhancement in magnetic field results in decrease in horizontal velocity and boundary layer becomes thinner. The obtained results are compared with the available results in the literature and found in excellent agreement in the limiting cases.