1Mn-substituted Ni-Zn spinel ferrites (Ni_0.5-yZn_0.5-zFe_2-xMn_x,y,zO₄, either one of x, y, z is 0.1) were synthesized by sol-gel and solidstate reaction methods, respectively. where their high-frequency and electromagnetic (EM) wave absorption properties were systematically studied. Single spinel phase was confirmed by X-ray diffraction (XRD) analysis for all the samples. Scanning electron microscope (SEM) was used for the microstructure observation. The complex permittivities (ε', ε'') and permeabilities (μ', μ'') spectra (0.1 ≤f ≤ 18 GHz) were measured by using a vector network analyzer on the ferrite-epoxy (10 wt%) composite samples. The reflective loss (RL) values which stands for the EM wave absorption performances were calculated from ε', ε'', μ', μ'' data based on transmission line theory. The sol-gel-processed ferrite-epoxy composites showed very low dielectric loss with composition-dependent μ'' spectra which is related to magnetic loss. All composite samples exhibited excellent absorption characteristics in the frequency range of 1~4 GHz, and the EM wave absorption characteristics changed depending on the preparation method and composition of the ferrite particles. The maximum absorption performance of RL = -68 dB was achieved on sol-gel-processed ferrite (Ni_0.4Mn_0.1Zn_0.5Fe₂O₄)-epoxy composites at the frequency of 2.5 GHz with absorber thickness of 7.3 mm. As for the wideband EM wave absorption, the ferrite samples synthesized by solid-phase reaction exhibited better performance than the sol-gel processed samples. Due to these characteristics, the Mn-Ni-Zn spinel ferrite composite is highly applicable as an electromagnetic wave absorbing material in the L, S-band (1~4 GHz) range operated for military aviation stealth.

In this work, we have investigated the effect of Molybdenum (Mo) content on the microstructure and magnetic properties of Fe_77.5Si_11.5B₇Mo_xNb_3-xCu₁ (x = 0~3 at.%) nanocrystalline soft magnetic alloys. Previous studies have reported that transition metal elements have a great effect on improving the glass forming ability (GFA) of amorphous alloys. In particular, Mo is expected to be most effective in improving GFA of amorphous alloys among various transition metal elements because it has a large atomic radius and a negative mixing enthalpy with metalloid elements. In this study, nanocrystalline ribbons with a composition of Fe_77.5Si_11.5B₇Nb_3-xMo_xCu₁ (x = 0~3) have been fabricated by rapid-quenching melt spinning and thermal annealing. It has been demonstrated that the addition of a small amount of Mo (1~3 at.%) to the alloy improves the GFA and significantly suppresses undesirable surface and internal crystallization during the melt spinning process. Among the alloys investigated in this work, Fe_77.5Si_11.5B₇Nb₀Mo₃Cu₁ nanocrystalline ribbon annealed at 580 ℃ have exhibited excellent soft-magnetic properties including lowest coercivity of 5 A/m, highest maximum relative permeability of 14340, and highest flux density.

FeCo-based amorphous materials have low coercivity, high saturation magnetization, and high permeability. These characteristics make them popular for use in various applications such as inductors, sensors, magnetic heads, electromagnetic cores, magnetic memories, current machines, and motors. This paper aims to explain studies on the quinary alloys in which Nb, Mo, Ta, and Cr are added to the Fe-Co-B-Si alloy known to have good soft magnetic properties, focusing on structural, thermal, and magnetic properties.

This paper covers from an initial design to an optimal design for the Interior Permanent Magnet Synchronous Motor (IPMSM), which is used for a neighborhood Electric Vehicle (NEV). The initial design is accomplished by prioritizing the decision of motor parameter range which are the induced voltage and the inductance that satisfy the output characteristics of the motor. This is an effective way to reduce trial and error in the initial design. The optimal design is achieved by using the experiment design method in combination with Finite Element Method. Generally, making the induced voltage sinusoidal and reducing the cogging torque is a way to minimize the torque ripple of the motor. In this paper, a design method was presented to effectively reduce torque ripple in IPMSM using the response surface method.

A low cogging torque and torque is the key performances of the motor with the required high precision drive. Therefore, skew design methods for stator and rotor have been widely applied to reduce cogging torque. However, the skew design has many weaknesses to increase cost and deteriorate performance due to the additional equipment and processes for manufacturing. In this study, a hybrid design method is proposed to reduce cogging torque and torque ripple by applying the asymmetry tooth tip of stator and rotor skew in permanent magnet synchronous motor, instead of using the conventional rotor skew design. The application case for the proposed method deals with the asymmetric tooth tip of stator and 2 step-skew rotor, which is equivalent to have the performance effects of 4 step-skew rotor. In order to verify the proposed method, cogging torque was compared using 2D finite element analysis (FEA). In addition, back-EMF and torque ripple are also compared.

We study the spin-pumping effect in topological insulator/ferromagnet structures using ferromagnetic resonance (FMR) measurements with a coplanar waveguide (CPW). We compared three different samples: NiFe, Bi₂Se₃/NiFe, and Bi₂Se₃/Ag/NiFe, where NiFe is a reference sample. Compared with 7 nm thick NiFe, Bi₂Se₃/NiFe shows three times larger magnetic damping, which is the consequence of the strong spin pumping effect from NiFe to Bi₂Se₃ layers. Surprisingly, once 1.5 nm thick Ag inserted between Bi₂Se₃ and NiFe, we could observe 12 times enlargement of a magnetic damping in Bi₂Se₃/Ag/NiFe structure. This observation can be attributed to the enhancement of Rashba orbit coupling at the Bi₂Se₃/Ag interface.

The IrMn thickness dependence of exchange bias training effect was studied in exchange coupled CoFe/IrMn(t_AF) thin films. The exchange bias training effect was dominated in the range of 3 nm < t_AF < 7 nm. The range was correspond to increasing the exchange bias by the pinned IrMn and decreasing the coercivity by the irreversible behavior of unpinned IrMn based on single domain model. Thus the exchange bias training effect was explained by the relaxation process by the reorientation of pinned-unpinned IrMn from initial alignment to final equilibrium state during the consecutive cycles of M-H loop.

The iron oxide nanoparticles (NPs) was synthesized by thermal decomposition method. The effective saturation magnetization M_eff =202 emu/cc and g-factor = 2.12 for iron oxide NPs was obtained by using ferromagnetic resonance (FMR) technique in 2D plate coated with NPs. The FMR signals of final reaction solution including NPs was analyzed by using kittel’s resonance condition for shape effect. The FMR signals of final reaction solution divided into two different signals. The one was due to the superparamagnetic 3D sphere by the isolated NPs, the other was explained by the 1D chains structure connected by NPs.