The vortex-driven magnetization process of micron-sized, exchange-coupled square elements with composition of Ni₈₀Fe₂₀ (12 nm)/Ir₂₀Mn₈₀ (5 nm) is investigated. The exchange-bias is introduced by field-cooling through the blocking temperature (T_B) of the system, whereby Landau-shaped vortex states of the Ni₈₀Fe₂₀ layer are imprinted into the Ir₂₀Mn₈₀. In the case of zero-field cooling, the exchange-coupling at the ferromagnetic/antiferromagnetic interface significantly enhances the vortex stability by increasing the nucleation and annihilation fields, while reducing coercivity and remanence. For the field-cooled elements, the hysteresis loops are shifted along the cooling field axis. The loop shift is attributed to the imprinting of displaced vortex state of Ni₈₀Fe₂₀ into Ir₂₀Mn₈₀, which leads to asymmetric effective local pinning fields at the interface. The asymmetry of the hysteresis loop and the strength of the exchange-bias field can be tuned by varying the strength of cooling field. Micromagnetic modeling reproduces the experimentally observed vortex-driven magnetization process if the local pinning fields induced by exchange-coupling of the ferromagnetic and antiferromagnetic layers are taken into account.

Steam generator tubes (SGTs) in nuclear power plants (NPPs) are a boundary between the primary side generating heat by nuclear fission and the secondary side generating electric power by a turbine. The water inside the SGT is high temperature and high pressure. Therefore, defects and magnetic phases (MPs) are partly produced in non-magnetic SGT by high stresses and temperatures. This causes trouble regarding the safety of SGTs but it is difficult to detect the MP using the conventional eddy current technique (ECT). In particular, a circumferential defect (CD) and circumferential magnetic phase (CMP) cannot detected by ECT. Consequently, a new method is needed to detect CDs and CMPs in SGT. A new U-type yoke with two types of coils was designed and the reactance signal by the CMPs and CDs in the SGT material was simulated.

This study investigated theoretically the properties of the spin transfer torque acting on a ferromagnet in a ferromagnet-normal metal-antiferromagnet junction. Earlier work showed that the angular dependence of the spin transfer torque can be a wavy-type if the junction satisfies a special symmetry. This paper reports a simple model analysis that allows a derivation of the wavy angular dependence without taking advantage of the symmetry. This result suggests that the wavy angular dependence can appear even when the symmetry is broken. As an illustration, the angular dependence was calculated as a function of the degree of the compensation at the normal metal-antiferromagnet interface. The implications of the result for the current-induced magnetization precession are discussed.

Bilayers of soft NiFe (150 nm-420 nm) on hard Ni (150 nm) were prepared by electrodeposition. The process of magnetization reversal in the NiFe/Ni bilayers was then investigated. The hysteresis loop generated by a magnetization reversal of soft NiFe under a positive saturation state of a hard Ni layer shows a shift along the negative field axis, which is clear evidence for the exchange spring effect in the NiFe/Ni bilayers. The dependence of the coercive field H_c and exchange bias field H_ex on the thickness of the NiFe layer was also investigated. As the NiFe thickness increases from 150 nm to 420 nm, both H_c and H_ex decrease rapidly from H_c= 51.7 Oe and H_ex = 12.2 Oe, and saturate to H_c = 5.8 Oe and H_ex = 3.5 Oe.

Solid solutions between BaTiO₃ and LaFeO₃ have been prepared through a solid state reaction method. The X-ray diffraction results reveal that Ba_1-xLa_xTi_1-xFe_xO₃ (0.1 ≤ x ≤ 0.7) compounds have a cubic structure, whereas the parent material BaTiO₃ has a tetragonal structure. The magnetization measurements indicate that the materials have a magnetic ordering at room temperature and the magnetic properties of the solid solutions depending on the doping amount of LaFeO₃. The origin of magnetic behaviors is believed to be from Fe³⁺ ions.

In the present study, we systematically investigated the effect of mechanical milling on the magnetic properties of Sm₂Fe₁₇N_x powders produced by the reduction-diffusion process. The Sm-Fe powders obtained by the reduction-diffusion process were composed of an Sm₂Fe₁₇ single phase. After nitrogenation, the coercivity and saturation magnetization of the powders were 0.48 kOe and 13.32 kG, respectively. The particle size largely decreased down to less than 2 ㎛ in diameter after ball milling for 30 hours. However, there is no evidence that the Sm₂Fe₁₇N_x was decomposed to Sm-N and α-Fe even after ball milling for 30 hours. The coercivity was significantly improved up to 8.82 kOe after milling for 60 hours. However, the magnetization decreased linearly with the ball milling time.

The electron spin resonance lineshape (ESRLS) function for the electron spin resonance linewidth (ESRLW) of Cr³⁺ (S = 3/2) in ferroelectric lithium niobate single crystals doped with 0.05 wt% of Cr, is obtained by using the projection operator technique (POT), developed by Argyres and Sigel. The ESRLS function is calculated to be axially symmetric about the c − axis and analyzed by using the spin Hamiltonian H_SP = μ_B (B · g^↔ · S) + S · D^↔ · S with the parameters g = 1.972 and D = 0.395 cm⁻¹. In the ca plane, the linewidths show a strong angular dependence, whereas in the ab plane, they are independent of the angle. This result implies that the resonance center has an axial symmetry along the c − axis. Further, from the temperature dependence of the linewidths that is shown, it can be seen that the linewidths increase as the temperature increases, at a frequency of v = 9.27GHz. This result implies that the scattering effect increases with increasing temperature. Thus, the POT is considered to be more convenient to explain the scattering mechanism as in the case of other optical resonant systems.

This paper presents a magnetization modeling method combined with material sensitivity information to identify the unknown magnetization distribution of a hull and improve the accuracy of the predicted fields. First, based on the magnetization modeling, the hull surface was divided into three-dimensional sheet elements, where the individual remanent magnetization was assumed to be constant. For a fast search of the optimum magnetization distribution on the hull, a material sensitivity formula containing the first-order gradient information of an objective function was combined with the magnetization modeling method. The feature of the proposed method is that it can provide a stable and accurate field solution, even in the vicinity of the hull. Finally, the validity of the method was tested using a scale model ship.

The design of an air compressor-driving quadratic linear actuator in a fuel cell BOP system is studied using orthogonal techniques. The approach utilizes an orthogonal array for design of ‘experiments’, i.e. the scheme for numerical simulations using a finite element method. Eco-friendly energy is increasingly important due to the depletion of fossil fuels and environmental pollution. Among the new energy sources, fuel cell is spotlighted as renewable energy because it produces few dusts. The air compressor performance is directly related to the efficiency of the fuel cell BOP system has high power consumption. In this paper, an optimized technique using an orthogonal matrix is applied to the design problem to improve the performance of quadratic linear actuator.

This study estimated experimentally the loss distribution caused by magnetic friction in magnetic parts of a superconductor flywheel energy storage system (SFES) to obtain information for the design of high efficiency SFES. Through the spin down experiment using the manufactured vertical shaft type SFES with a journal type superconductor magnetic bearing (SMB), the coefficients of friction by the SMB, the stator core of permanent magnet synchronous motor/generator (PMSM/G), and the leakage flux of the metal parts were calculated. The coefficients of friction by the stator core of PMSM/G in case of using Si-steel and an amorphous core were calculated. The energy loss by magnetic friction in the stator core of PMSM/G was much larger than that in the other parts. The level of friction loss could be reduced dramatically using an amorphous core. Energy loss by the leakage magnetic field was small. On the other hand, the energy loss could be increased under other conditions according to the type of metal nearby the leakage magnetic fields. In manufactured SFES, the rotational loss by the amorphous core was approximately 2 times the loss of the superconductor and leakage. Moreover, the rotational loss by the Si-steel core is approximately 3~3.5 times the loss of superconductor and leakage.

This paper shows the entire future market volume of the HTS power industry, one of main smart grid equipment, in the case of the final market penetration ratio reaching 100% in the domestic market (South Korea). In this paper, the market penetration ratio is determined using the judgment method, with the market penetration S-curve induced using the Delphi method and the Product Life Cycle from 2011 (supposed launching year, not realistic physical year), to 2050 (expected final target year). This paper analyzes the HTS market penetration ratio of each stage, apparent innovation, early adapters, and the early/late majority and laggard stage,using the S-curve, thus calculating the total future market volume of HTS equipment in the positive sense. Finally, this paper estimates the quantitative analysis results for the HTS4-items (cable, FCL, transformer, rotation machine) of each year within the domestic market.

We report on a numerical calculation study of two new functional properties in magnetic tunnel junctions (MTJs), negative dynamic resistance and RF amplification. The magnetic dynamics in a conventional CoFeB/MgO/CoFeB MTJ with in-plane magnetization was investigated using a macro-spin model simulation. To examine the influence of thermal fluctuations, random external magnetic fields were also included. Using a voltage controlled bias circuit, the negative dynamic resistance was obtained from time averaged I-V characteristics at both 0 K and 300 K under appropriate external magnetic fields and bias voltages. Using this negative dynamic resistance property, we demonstrated RF amplification with a 100 MHz high frequency signal. Sizable RF amplification gain was observed without thermal fluctuation. However, at 300 K, the RF signal was not amplified because low frequency magnetization dynamics were dominant.

The coercivity H_c of Nd₂Fe₁₄B magnets and Nd₂Fe₁₄B/(Nd_0.7Dy_0.3)₂Fe₁₄B composite magnets were calculated by computer simulation based on the micromagnetic theory under assumptions that Nd₂Fe₁₄B and (Nd_0.7Dy_0.3)₂Fe₁₄B grains have magnetically deteriorated layers on their surfaces and diffusion of Dy from (Nd_0.7Dy_0.3)₂Fe₁₄B grains to Nd₂Fe₁₄B ones through the contacting boundaries recovers the magnetic anisotropy of the deteriorated layers of Nd₂Fe₁₄B grains. H_c of Nd₂Fe₁₄B/(Nd_0.7Dy_0.3)₂Fe₁₄B composite magnets increased by the diffusion of Dy from (Nd_0.7Dy_0.3)₂Fe₁₄B grains to Nd₂Fe₁₄B ones and the resultant recovery of the anisotropy field of deteriorated layers of Nd₂Fe₁₄B grains. The H_c vs fraction of (Nd_0.7Dy_0.3)₂Fe₁₄B grains curve were convex for the magnets with the degree of alignment between 0.94 and 0.99, which suggests that the above composite magnets have larger H_c values than the alloy-magnets with the same Dy content, and that we can save the consumption of Dy by using these composite magnets.

Magnetoelectric (ME) transducers were originally intended for magnetic field sensors but have recently been used in vibration energy harvesting. In this paper, a new broadband vibration energy harvester has been designed and fabricated to be efficiently applicable over a range of source frequencies, which consists of two cantilever beams, two magnetoelectric (ME) transducers and a magnetic circuit. The effects of the structure parameters, such as the non-linear magnetic forces of the ME transducers and the magnetic field distribution of the magnetic circuit, are analyzed for achieving the optimal vibration energy harvesting performances. A prototype is fabricated and tested, and the experimental results on the performances show that the harvester has bandwidths of 5.6 Hz, and a maximum power of 0.25 mW under an acceleration of 0.2 g (with g = 9.8 ms²).

The magnetostrictive material is magnetized in magnetic field and produces a nonuniform demagnetizing field inside and outside it. The demagnetization is decided by the permeability of magnetostrictive material and its size. The magnetoelectric performances are determined by the synthesis of the applied and demagnetizing fields. An analytical model is proposed to predict the magnetoelectric voltage coefficient (MEVC) of magnetostrictive/piezoelectric laminate composite using equivalent circuit method, in which the nonuniform demagnetizing field is taken into account. The theoretical and experimental results indicate that the MEVC is positively connected with the permeability and the piezomagnetic coefficient of magnetostrictive material. To obtain the maximum MEVC, both the permeability and the piezomagnetic coefficient of magnetostrictive material should be taken into account in selecting the suitable magnetostrictive material.

We report results of first principles calculations for effects of an external electric field (E-field) on the magnetocrystalline anisotropy (MCA) in transition-metal (Fe, Co, and Ni) monolayers and at metal-insulator (Fe/MgO) interfaces by means of full-potential linearized augmented plane wave method. For the monolayers, the MCA in the Fe monolayer (but not in the Co and Ni) is modified by the E-field, and a giant modification is achieved in the Fe_0.75Co_0.25. For the Fe/MgO interfaces, the ideal Fe/MgO interface gives rise to a large out-ofplane MCA, and a MCA modification is induced when an E-field is introduced. However, the existence of an interfacial FeO layer between the Fe layer and the MgO substrate may play a key role in demonstrating an Efield-driven MCA switching, i.e., from out-of-plane MCA to in-plane MCA.

Magnetic nanoparticles can potentially be used in drug delivery systems and for hyperthermia therapy. The applicability of Fe₃O₄, CoFe₂O₄, MgFe₂O₄, and NiFe₂O₄ nanoparticles for the same was studied by evaluating their magnetization, thermal efficiency, and biocompatibility. Fe₃O₄ and CoFe₂O₄ nanoparticles exhibited large magnetization. Fe₃O₄ and NiFe₂O₄ nanoparticles exhibited large induction heating. MgFe₂O₄ nanoparticles exhibited low magnetization compared to the other nanoparticles. NiFe₂O₄ nanoparticles were found to be cytotoxic, whereas the other nanoparticles were not cytotoxic. This study indicates that Fe₃O₄ nanoparticles could be the most suitable ones for hyperthermia therapy.

This study reports an alternative method for measuring the magnetoresistance of unpatterned magnetic tunnel junctions similar to the current-in-plane tunneling (CIPT) method. Instead of using microprobes, a series of point contacts with different spacings are coated on the top surface of the junctions and R-H loops at various spacings are then measured by the usual four-point probe method. The values of magnetoresistance and resistance-area products can be obtained by fitting the measured data to the CIPT theoretical model. The test results of two types of junctions were highly similar to those obtained from standard CIPT tools. The proposed method may help to accelerate the process for evaluating the quality of magnetic tunnel junctions when commercial CIPT tools are not accessible.

Fe-Cr alloys with different Cr contents were prepared by an arc melting technique. The alloys were isochronally aged in the range from 400 ℃ to 900 ℃ with 50 ℃ steps with a holding time of 100 hours. The ageing produced embrittlement in the alloys due to either the formation of a Cr-rich α| phase or a σ phase at high temperatures. Magnetic Hysteresis Loop (MHL) and Micro-Vickers hardness were measured at each step to correlate the magnetic and mechanical properties. Coercivity and hardness of the alloys were increased and remanence decreased up to 500-550 ℃ due to formation of a Cr-rich α| phase. Beyond 500-550 ℃ range, the coercivity and hardness decreased and remanence increased due to the coarsening or dissolution of the Cr-richα| phase. In the Fe-48% Cr alloy, formation of the σ phase at 700 ℃ reduced the maximum induction of the alloy significantly.

0.30 mm thick and 90 mm wide thin foils made of Fe-6.5wt.%Si alloy were successfully fabricated by traditional rolling. The as-rolled sheets had good shapes and shining metal luster. The effects of annealing temperature on the magnetic properties of the sheets were investigated. Excellent Dc properties (H_c: 11.55 A/m, μ_m: 23710, and B_s: 1.439 T) were obtained at an annealing temperature of 1453 K for 1.5 h. At low frequencies (≤ 1 kHz), heat treatment temperature has little effect on iron loss which remained at the level of 9.8 W/kg. Annealing at 1273 K for 1.5 h is optimum for frequencies above 5 kHz.

To improve trapped field characteristics of a high temperature superconducting (HTS) bulk, a technique to implement artificial holes has been studied. The artificial holes, filled up with epoxy or metal, may provide better cooling channel and enhance mechanical strength of the HTS bulk. Although many useful researches based on experiments have been reported, a numerical approach is still limited because of several reasons that include: 1) highly non-linear electromagnetic properties of HTS; and 2) difficulty in modeling of randomly scattered “small” artificial holes. In this paper, a 2-D finite element method with iteration is adopted to analyze trapped field characteristics of HTS bulk with artificial holes. The validity of the calculation is verified by comparison between measurement and calculation of a trapped field in a 40 × 40 mm square and 3.1 mm thick HTS bulk having 16 artificial holes with diameter of 0.7 mm. The effects of sizes and array patterns of artificial holes on distribution of trapped field within HTS bulk are numerically investigated using suggested method.

YBa₂C₃O_7-x films were fabricated on a SrTiO₃ (100) substrate using a trimethylaceate propionic acid (TMAP)-based MOD process by controlling the precursor solution viscosity, firing temperature, and by using various coatings. The viscosity of the precursor solution was controlled by the addition of Xylenes. The films were heat treated with different temperatures from 750 to 800 ℃. c-axis oriented films were obtained. After adding 9 ml of Xylene into the precursor solution, the T_c of the YBCO film, which was coated 2 times and heat treated at 800 ℃, was 86 K and the measured J_c was above 2.5 MA/cm² at 77 K in a zero-field.

The phase transition of vortex matter from solid to liquid was studied in iron-based superconductors. Based on the traditional vortex glass theory, we have examined the magnetoresistivity data of iron-based superconductors using our extended thermal activation model: ρ(B,T) = ρ((T-T_g(B))/(T_c(0)-T_g(B)))^v(z-1). We predict that the magnetic field-dependent area S + S₀ which integrates ρ with T is proportional to B^β, where β is the vortex glass transition exponent. From our calculation, the vortex glass transition exponent is 0.33, close to the exponent of area S₀+ S is 0.31 in SmO_0.9F_0.1FeAs; the exponent of area S is 0.63, which is close to the irreversibility line exponent 2/3. Both of the results show the validity of our model. In addition, our model is shown to be effective in describing irreversibility behavior in layered superconductors.