Synthetic antiferromagnets (SAFs) are used as free layer structures for various magnetic devices utilizing spintransfer torque (STT). Therefore, it is important to understand current-induced excitation of SAFs. By means of drift-diffusion and macrospin models, we studied the current-induced excitation of a SAF-free layer structure (NiFe/Ru/NiFe). The simulation results were compared with the previous experimental results [N. Smith et al., Phys. Rev. Lett. 101, 247205 (2008)]. We confirmed that a nonzero STT through the Ru layer is essential for explaining the experimental results.

The HDDR (hydrogenation, disproportionation, desorption, and recombination) process can be used as an effective way of converting a no coercivity Nd-Fe-B ingot material, with a coarse Nd₂Fe₁₄B grain structure, to a highly coercive one with a fine grain structure. Careful control of the HDDR process can lead to an anisotropic powder with good Nd₂Fe₁₄B grain texture; the most critical step for inducing texture is disproportionation. The critical conditions (hydrogen pressure and temperature) for the disproportionation reaction of fully hydrogenated Nd_12.5Fe_81.1-(x+y)B_6.4Ga_xNb_y (x = 0 or 0.3, y = 0 or 0.2) alloys, in different atmospheres of pure hydrogen and a mixed gas of hydrogen and argon, was investigated with TPA (thermopiezic analyser). From this, the hydrogen pressure-temperature diagram showing the critical conditions was established. The critical disproportionation temperature of the fully hydrogenated Nd_12.5Fe_81.1-(x+y)B_6.4Ga_xNb_y alloys was slightly increased as the hydrogen pressure decreased in both pure hydrogen and mixed gas. The critical disproportionation temperature of the hydrogenated alloys was higher in the mixed gas than in pure hydrogen. Addition of Ga and Nb increased the critical disproportionation temperature of the fully hydrogenated Nd-Fe-B alloys.

The Zn, Co and Ni substituted manganese ferrite powders, Mn_1-x(Zn, Co, Ni)_xFe₂O₄, were fabricated by the solgel method, and their crystallographic and magnetic properties were studied. The Zn substituted manganese ferrite, Zn_0.2Mn_0.8Fe₂O₄, had a single spinel structure above 400 ^oC, and the size of the particles of the ferrite powder increased when the annealing temperature was increased. Above 500 ^oC, all the Mn_1-x(Zn, Co, Ni)_xFe₂O₄ ferrite had a single spinel structure and the lattice constants decreased with an increasing substitution of Zn, Co, and Ni in Mn_1-x(Zn, Co, Ni)_xFe₂O₄. The Mössbauer spectra of Mn_1-xZn_xFe₂O₄ (0.0≤x≤0.4) could be fitted as the superposition of two Zeeman sextets due to the tetrahedral and octahedral sites of the Fe³⁺ ions. For x = 0.6 and 0.8 they showed two Zeeman sextets and a single quadrupole doublet, which indicated they were ferrimagnetic and paramagnetic. And for x = 1.0 spectrum showed a doublet due to a paramagnetic phase. For the Co and Ni substituted manganese ferrite powders, all the Mössbauer spectra could be fitted as the superposition of two Zeeman sextets due to the tetrahedral and octahedral sites of the Fe³⁺ ions. The variation of the Mössbauer parameters are also discussed with substituted Zn, Co and Ni ions. The increment of the saturation magnetization up to x = 0.6 in Mn_1-xCo_xFe₂O₄ could be qualitatively explained using the site distribution and the spin magnetic moment of substituted ions. The saturation magnetization and coercivity of the Mn_1-x(Zn, Co, Ni)_xFe₂O₄ (x = 0.4) ferrite powders were also compared with pure MnFe₂O₄.

Li_0.1Zn_0.9O and MgFe₂O₄ powders were synthesized using chemical methods and mixed in different proportions to prepare a mixture of Li_0.1Zn_0.9O and MgFe₂O₄ that was thermally treated between 900 to 1100 ^oC for 1 hour. Structural characterization was done using X-ray powder diffraction measurements. Grain sizes and morphologies of Li_0.1Zn_0.9O, MgFe₂O₄, and Li_0.1Zn_0.9O+MgFe₂O₄ samples were observed using a scanning electron microscope. Variation of magnetic properties of the Li_0.1Zn_0.9O+MgFe₂O₄ samples due to the addition of Li_0.1Zn_0.9O was studied in relation to the structural changes occurring due to the thermal treatment. In particular, changes in the cationic distribution between the tetrahedral and octahedral positions were studied with respect to the increase of the annealing temperature. Magnetization was found to be dependent on the cations distributed in the tetrahedral and octahedral sites of the MgFe₂O₄.

The coercivity mechanism in permanent magnets was analyzed according to the effects of domain nucleation and domain wall pinning. The coercivity mechanism of a TbCo thin film with high perpendicular magnetic anisotropy was considered in terms of the local inhomogeneity in the thin film. The initial magnetization curves of the TbCo thin films demonstrated domain wall pinning to be the main contributor to the coercivity mechanism than domain nucleation. Based on the coercivity model proposed by Kronmüller et al., the inhomogeneity size acting as a domain wall pinning site was determined. Using the measured values of perpendicular anisotropy constant (K_u), saturation magnetization (M_s), and coercivity (H_c), the inhomogeneity size estimated in a TbCo thin film with high coercivity was approximately 9 nm.

A new kind of magnetic rubber, Fe dispersed ethylene propylene monomer (EPM), was prepared by a conventional technique using a two roll mill. The magnetic fillers of Fe-nanoparicles were coated by low density polyethylene (LDPE). The purpose of surface treatment of nanoparticles by LDPE is to enhance wettability and lubricancy of the fillers in a polymer matrix. The mechanical strength and microstructure of the magnetic rubber were characterized by tensile strength test and scanning electron microscopy (SEM). Results revealed that the Fe nanoparticles were relatively well dispersed in an EPM matrix. It was found that the nano- Fe dispersed magnetic rubber showed higher coercivity and tensile strength than those of micron- Fe dispersed one.

We have investigated the effects of post annealing on iron oxide nanoparticles synthesized by the novel hydrothermal synthesis method with the FeSO₄·7H₂O. To investigate the post annealing effect, the as-synthesized iron oxide nanoparticles were annealed at different temperatures in a vacuum chamber. The morphological, structural and magnetic properties of the iron oxide nanoparticles were investigated with high resolution X-ray powder diffraction (XRD), high resolution transmission electron microscopy (HRTEM), Mössbauer spectroscopy, and vibrating sample magnetometer analysis. According to the XRD and HRTEM analysis results, as-synthesized iron oxide nanoparticles were only magnetite (Fe₃O₄) phase with face-centered cubic structure but post annealed iron oxide nanoparticles at 700 ^oC were mainly magnetite phase with trivial maghemite (γ -Fe₂O₃) phase which was induced in the post annealing treatment. The crystallinity of the iron oxide nanoparticles is enhanced by the post annealing treatment. The particle size of the as-synthesized iron oxide nanoparticles was about 5 nm and the particle shape was almost spherical. But the particle size of the post annealed iron oxide nanoparticles at 700 ^oC was around 25 nm and the particle shape was spherical and irregular. The as-synthesized iron oxide nanoparticles showed superparamagnetic behavior, but post annealed iron oxide nanoparticles at 700 ^oC did not show superparamagnetic behavior due to the increase of particle size by post annealing treatment. The saturation of magnetization of the as-synthesized nanoparticles, post annealed nanoparticles at 500 ^oC, and post annealed nanoparticles at 700 ^oC was found to be 3.7 emu/g, 6.1 emu/g, and 7.5 emu/g, respectively. The much smaller saturation magnetization value than one of bulk magnetite can be attributed to spin disorder and/or spin canting, spin pinning at the nanoparticle surface.

Spin polarized tunneling through a hybrid tunnel barrier of a Spin filter (SF) based on a EuO ferro-magnetic semiconductor and an organic semiconductor (OSC) (rubrene in this case) was investigated. For quasi-magnetic tunnel junction (MTJ) structures, such as Co/rubrene/EuO/Al, we observed a strong spin filtering effect of the EuO layer exhibiting I-V curves with high spin polarization (P) of up to 99% measured at 4 K. However, a magnetoresistance (MR) value of 9% was obtained at 4.2 K. The low MR compared to the high P could be attributed to spin scattering caused by structural defects at the interface between the EuO and rubrene, due to nonstoichiometry in the EuO.

The design of joints in a transformer core significantly affects the transformer’s efficiency. Air gaps cause variations in the flux distribution at the joints of the laminations, which depend on the geometry. Two similar samples consisting of electrical steel strips and amorphous ribbons were made. The spatial flux distributions were determined using an array of search coils for each sample. 2D models of these samples were created and examined by finite element analysis. The magnetic flux distribution for each lamination in the samples was computed. The results show that the flux density in amorphous ribbons above and below the air gap starts to approach saturation at lower flux density levels than for electrical steel. The flux density measured using the search coil under the air gap is increased in amorphous ribbons and decreased in the electrical steel with increasing frequency.

In our present work, we developed a GMI (giant magnetoimpedance) sensor system to detect magnetic fields in the milli gauss range based on the asymmetric magnetoimpedance (AGMI) effect in Co-based amorphous ribbon with self bias field produced by field-annealing in open air. The system comprises magnetoimpedance sensor probe, signal conditioning circuits, A/D converter, USB controller, notebook computer, and program for measurement and display. Sensor probe was constructed by wire-bonding the cobalt based amorphous ribbon with dimensions 10 mm × 1 mm × 20 ㎛ on a printed circuit board. Negative feedback was used to remove the hysteresis and temperature dependence and to increase the linearity of the system. Sensitivity of the milli gauss meter was 0.3 V/Oe and the magnetic field resolution and environmental noise level were less than 0.01 Oe and 2 mOe, respectively, in an unshielded room.

This paper discusses the effectiveness of high magnetization saturation in ILI (In-Line Inspection) using an MFL (Magnetic Flux Leakage) tool, and introduces a practical method for improving the magnetization level together with the piggability. Thin steel plates, replacing the conventional wire brushes were used as conductors to transfer the magnetic flux to the pipe wall. The newly designed MFL tool was compared with the conventional version by means of FEM (Finite Element Method) analysis and full-scale experiments. In the results, the newly developed magnetization system obtained a stronger MFL signal amplitude, specially 2.7 times stronger, than that obtained by the conventional magnetization system for the same defect dimensions.

Local wall thinning in pipelines affects the structural integrity of industries like nuclear power plants (NPPs). In the present study, a pulsed eddy current (PEC) differential probe with two excitation coils and two Hall-sensors was fabricated to measure the wall thinning in insulated pipelines. A stainless steel test sample was prepared with a thickness that varied from 1 mm to 5 mm and was laminated by plastic insulation to simulate the pipelines in NPPs. The excitation coils in the probe were driven by a rectangular current pulse, the difference of signals from two Hall-sensors was measured as the resultant PEC signal. The peak value of the detected signal is used to describe the wall thinning. The peak value increased as the thickness of the test sample increased. The results were measured at different insulation thicknesses on the sample. Results show that the differential PEC probe has the potential to detect wall thinning in an insulated NPP pipelines.

Photoplethysmogram (PPG) and pressure pulse waveform (PPW) were compared and evaluated for the efficacy of stimulating knuckles by using the pulsed magnetic field. Both signals were observed simultaneously while the knuckles were exposed for 10 min to the pulsed magnetic field, with maximum field intensity of 0.8 T and transition time of 0.126 msec. After 5 min stimulation of the knuckles, the results showed that the aging indexes calculated from the second derivative of the PPG were increased from −1.913 to 0.072, and that of the PPW from −0.063 to 0.387. However, for the relatively long-term stimulation for 10 min, we found that the values of both the aging indexes of the second derivatives and augmentation index of the PPW returned to the starting level. The changes observed in characteristic factors such as the aging indexes of the second derivatives and augmentation index of the PPW indicate the potential of pulsed magnetic field stimulation as a therapeutic method for the treatment of patients with peripheral vascular disease.

Since the hypothalamus immediately reacts to a nerve by processing all the information from the human body and the external stimulus being conducted, it performs a significant role in internal secretion; thus, a diverse and rapid stimulus pulse is required. By detecting Zero Detector accurately via the application of AVR on-Chip (ATMEL) using commercial electricity, chopping generates a stimulus pulse to the brain using an IGBT gate to designate a new magnetic stimulation following treatment and diagnosis. To simplify and generate a diverse range of stimuli for the brain, chopping can be used as a free magnetic stimulator. Then, commercial frequency (60Hz) is chopped precisely at the first level of the leakage transformer to deliver an appropriate stimulus pulse towards the hypothalamus when necessary. Discharge becomes stable, and the chopping frequency and duty-ratio provide variety after authorizing a high-pressure chopping voltage at the second level of the magnetic stimulator. These methods have several aims. The first is to apply a variable stimulus pulse via accurate switching frequency control by a voltaic pulse or a pulse repetition rate, according to the diagnostic purpose for a given hypothalamus. Consequently, the efficiency tends to increase. This experiment was conducted at a maximum of 210 W, a magnetic induced amplitude of 0.1~2.5 Tesla, a pulse duration of 200~350 μs, magnetic inducement of 5 Hz, stimulus frequency of 0.1~60 Hz, and a duration of stimulus train of 1~10 sec.

A laboratory sensor model was designed, constructed, and tested based on a newly proposed working principle of magnetic field detection. The principle of sensing employed a time-coded method in correlation with exploiting the advantageous features of the GMI effect. The sensor demonstrated a sensitivity of 10 μs/μT in the field range of ±100 μT. The sensing element in the form of an amorphous thin wire, 100 ㎛ in diameter × 50 mm long, was fit into a small field modulation coil of 60 mm length. At a magnetic field modulation in the range of hundreds of Hz, the change in time interval of two adjacent GMI voltage peaks was linearly related to the external magnetic field to be measured. This mechanism improved the sensor linearity of the GMI sensor to better than 0.2% in the measuring range of ±100 μT.