The convergence behavior of the all-electron full-potential linearized augmented plane-wave (FLAPW) method with the explicit orthogonalization (XO) scheme is tested on ferromagnetic bulk body-centered-cubic Fe. Applying a commonly used criterion relating the plane-wave and angular momentum cutoffs, l_max = R_MTK_max, where RMT is the muffin-tin (MT) sphere radius and Kmax is the plane-wave cutoff for the basis − the total energy is converged and stable for KmaxR_MT = 10. The total energy convergence dependence on the star-function cutoff, Gmax, is minimal and so a Gmax of 3K_max or a large enough G_max is a reasonable choice. We demonstrate that the convergence with respect to l_max or a fixed large enough G_max and K_max are independent, and that K_max provides a better measure of the convergence than R_MTK_max. The dependence of the total energy on R_MT is shown to be small if the core states are treated equivalently, and that the XO scheme is able to treat systems with significantly smaller R_MT than the standard LAPW method. For converged systems, the calculated lattice parameter, bulk modulus, and magnetic moments are in excellent agreement with the experimental values.

This study examined the structure and perpendicular magnetization of FePt films grown on Pt/Fe/MgO(100) buffered Si(100) substrates by molecular beam epitaxy. The [Fe(0.17nm)/Pt(0.2nm)]_N multilayers were prepared at room temperature to form a L1₀-FePt phase after vacuum annealing. Perpendicular magnetic anisotropy (PMA) was observed in the films after at least 15 repetitions (N = 15) of Fe/Pt deposition and annealing at 300 ^oC for 1 hour. Careful structural analysis of the films was carried out by x-ray diffraction and high-resolution transmission electron microscopy. These results will assist in the development of the low temperature L1₀- FePt deposition process, which will be essential for future extremely high density magnetic recording media.

We report the exchange bias in antiferromagnet/ferrimagnet Cr₂O₃/Fe₃O₄ core/shell nanoparticles. The magnetic field hysteresis curve for Cr₂O₃/Fe₃O₄ nanoparticles after field-cooling (FC) clearly showed both horizontal (H_EB~610 Oe) and vertical (ΔM~5.6 emu/g) shifts at 5 K. These shifts disappeared as the temperature increased toward the Neel temperature of Cr₂O₃ (T_N~307 K). The H_EB and ΔM values were sharply decreased between the 1^st and the 2^nd magnetic field cycles, and then slowly decreased with further cycling. These results are discussed in terms of the formation of single domains with pinned, uncompensated, antiferromagnetic spin and their evolution into multi-domains with cycling.

The effect of Ga and, Nb addition on the kinetics and mechanism of the disproportionation of a Nd-Fe-B alloy were investigated by isothermal thermopiezic analysis (TPA) using Nd_12.5Fe_(81.1-(x+y))B_6.4Ga_xNb_y (x=0 and 0.3, y= 0 and 0.2) alloys. The addition of Ga and Nb retarded the disproportionation kinetics of the Nd-Fe-B alloy significantly, and increased the activation energy of the disproportionation reaction. The disproportionation kinetics of the Nd_12.5Fe_(81.1-(x+y))B_6.4Ga_xNb_y alloys measured under an initial hydrogen pressure of 0.02 MPa were fitted to a parabolic rate law. This suggested that during the disproportionation of Nd_12.5Fe_(81.1-(x+y))B_6.4Ga_xNb_y alloys with an initial hydrogen pressure of 0.02 MPa, a continuous disproportionation product is formed and the overall reaction rate is limited by the diffusion of hydrogen atoms (or ions).

This study examined the effects of a decrease in thickness of magnetic alloy flakes on the electromagnetic wave absorption characteristics of nanocrystalline Fe_73.5Cu₁Nb₃Si1_5.5B₇ (at.%) alloy flakes/polymer composite sheets available for a quasi-microwave band. The thickness of FeCuNbSiB alloy flakes decreased to 1-2 ㎛ with increasing milling time up to 24 h, and the composite sheet including alloy flakes milled for 24 h exhibited considerably enhanced power loss properties in the GHz range compared to the sheets having non-milled alloy powders. Although a considerable increase in loss factor upon milling was observed in the narrow frequency range of 4-6 GHz, there was no correlation between the complex permeability and flake thickness. However, the complex permittivity increased with increasing milling time, and there was good agreement between the milling time and the frequency dependences of the complex permittivity and power loss.

Iron-doped Sn_1-xFe_xO₂ (x = 0.0, 0.05, 0.1, 0.2, 0.33) thin films on Si(100) substrates and powders were prepared by a chemical solution process. The x-ray diffraction (XRD) patterns of the Sn_1-xFe_xO₂ thin films and powders showed a polycrystalline rutile tetragonal structure. Thermo gravimetric (TG) - differential thermal analysis (DTA) showed the final weight loss above 430^oC for all powder samples. According to XRD Rietveld refinement of the powders, the lattice parameters and unit cell volume decreased with increasing Fe content. The magnetic properties were characterized using a vibrating sample magnetometer (VSM) and Mössbauer spectroscopy. The thin film samples with x = 0.1 and 0.2 showed paramagnetic properties but thin films with x = 0.33 exhibited ferromagnetic properties at room temperature. Mössbauer studies revealed the Fe³⁺ valence state in the samples. The ferromagnetism in the samples can be interpreted in terms of the direct ferromagnetic coupling of ferric ions via an electron trapped in a bridging oxygen deficiency, which can be explained using the Fcenter exchange model.

Nano-sized Yttrium iron garnet (YIG;Y₃Fe₅O₁₂) particles have been synthesized by using coprecipitation and a heat treatment process. The YIG particles were made using a nitrate or a chloride salt solution. The pH concentration of the solution was fixed at 12. Spherical shaped YIG particles were made with a size of about 20 nm. The magnetization value of the particles was smaller than the bulk value but their coercive field showed a high value.

We propose a new type of spin torque nano-oscillator structure with an exchange- biased free rotating layer. The proposed spin torque nano-oscillator consists of a fixed layer and a free rotating layer with an additional anti-ferromagnetic layer, which leads to an exchange bias in the free rotating layer. The spin dynamics of the exchange-biased free rotating layer can be described as an additional exchange field because the exchange bias manifests itself by the existance of a finite exchange bias field. The exchange bias field plays a similar role to that of a finite external field. Hence, microwave generation can be achieved without an external field in the proposed structure.

Nanolithography by atomic force microscope local oxidation was applied to the fabrication of planar-type Ni/Ni oxide/Ni junctions from 10 nm-thick Ni films. The junction characteristics were sensitive to the lithography conditions such as the bias voltage. Successful oxidation produced junctions of nonlinear current-voltage characteristics, implying the formation of oxide barriers. Magnetoresistance (MR) at low temperatures resembled that of spin valves.

This paper describes the design and analysis of a tubular linear actuator for intelligent AAP (Active Accelerate Pedal) system. In a driving emergency, the electromagnetic actuator produces an additional pedal force such as the active pedal force and vibration force to release the driver’s foot on accelerator pedal. A prior study found that the linear actuator with a ferromagnetic core had a problem in transferring the additional force naturally to a driver due to the cogging force. To reduce the cogging force and obtain higher performance of the AAP system, a coreless tubular linear actuator is suggested. Electromagnetic finite element analysis is executed to analyze and design the coreless tubular actuator, and dynamic analysis is performed to characterize the dynamic performance of the AAP system with the suggested tubular actuator for two types of thrust force.