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To investigate the structural effect on the ferroelectric electron emission, the electric field distribution in a two-dimensional structure was calculated as a function of thickness and upper electrode diameter, and the switching charge density and emission charge were measured simultaneously. The simulation results of the electric field distribution showed that an asymmetric electrode structure caused a stray field on the bare surface of the ferroelectric cathode near the edge of upper electrode. The distance of the stray field from the electrode edge increased with increasing ferroelectric thickness, but it did not depend on the upper electrode diameter. The switching charge density increased more on the cathode with thicker ferroelectric and smaller upper electrode diameter. This was attributed to the difference of field distribution on the bare ferroelectric surface near the electrode edge. The expanded stray field for the thicker ferroelectric cathode enhanced polarization switching near the electrod...

The dielectric and piezoelectric properties of sol–gel derived (x)Pb(Mg1/3Nb2/3)O3–(1−x)Pb(Zr1/2Ti1/2)O3[(x)PMN–(1−x)PZT] thin films were investigated as a function of PMN content (x=0–1). For all compositions in the (x)PMN–(1−x)PZT thin films, a well-developed perovskite phase with (111) preferred orientation was obtained at the annealing temperature range of 700–800 °C. With increasing PMN content, the dielectric constant increased, while the remnant polarization and coercive field decreased. The enhanced dielectric properties were shown in the region of x=0.2. At this composition, the dielectric constant and remnant polarization were 1750 and 12.75 μC/cm2, respectively, which indicate that the morphotropic phase boundary (MPB) exists near the composition of x=0.2. The transverse piezoelectric coefficient (d31) showed a maximum value of −84 pC/N at x=0.2. These results confirmed that enhancement of the dielectric constant and remnant polarization improved the piezoelectric properties at the MPB.

We calculate the electronic structures of FePt and Fe0.5Mn0.5Pt using first-principles calculations based on density functional theory within the local-spin-density approximation. The Curie temperature (Tc) was calculated by mean field approximation. Composition dependence of the Cure temperature (Tc(x)) of Fe1−xMnxPt was used to identify a composition to meet the desired Tc in the range of 600–650 K. The identified composition (0.0294 ≤ x ≤ 0.0713) gives saturation magnetization (Ms) in the range of 1041–919 emu/cm3 and magnetocrystalline anisotropy constant (K) in the range of 9.96–8.36 × 106 J/m3 at 0 K. Temperature dependent M(T) and K(T) of Fe1−xMnxPt (0.0294 ≤ x ≤ 0.0713) were calculated using the Brillouin function and Callen-Callen experimental relation, respectively. Fe1−xMnxPt (0.0294 ≤ x ≤ 0.0713) shows 930–800 emu/cm3 of Ms and 7.18–5.61 × 106 J/m3 of K at 300 K, thereby satisfying desired magnetic properties for heat-assisted magnetic recording media to achieve 4 Tb/in.2 areal density.

The wetting control of graphene is of great interest for electronic, mechanical, architectural, and bionic applications. In this study, the wettability of graphene-laminated micropillar structures was manipulated by changing the height of graphene-laminated structures and employing the trichlorosilane (HDF-S)-based self-assembly monolayer. Graphene-laminated micropillar structures with HDF-S exhibited higher hydrophobicity (contact angle of 129.5°) than pristine graphene thin film (78.8°), pristine graphene-laminated micropillar structures (97.5°), and HDF-S self-assembled graphene thin film (98.5°). Wetting states of the graphene-laminated micropillar structure with HDF-S was also examined by using a urea solution, which flowed across the surface without leaving any residues.

We demonstrate that magnetic loss tangent of M-type hexaferrite can be controlled by a small dc magnetic field, thereby improving radio frequency (RF) antenna radiation efficiency and realizing antenna miniaturization. Magnetic loss tangent (tan δμ) of the M-type BaFe9.6Co1.2Ti1.2O19 hexaferrite at 200 MHz decreased significantly from 11.8% to less than 1% as the applied dc magnetic field increased from 0 to 400 Oe. This is because the contribution of domain wall motion to permeability dispersion is decreased, and the ferromagnetic resonance frequency increases with the magnetic field. Antenna simulation results showed that radiation efficiency of the designed ferrite helical antenna increased from −22.9 to −9.2 dB with dc magnetic field of 400 Oe. Therefore, the small dc magnetic field played a key role in reduction of tan δμ of hexaferrite and improvement of antenna performance in the RF range.

We have studied soft M-type BaFe9.6Co1.2Ti1.2O19 hexaferrite for T-DMB (terrestrial digital media broadcasting) antenna applications. The effect of magneto-dynamic properties on antenna size, bandwidth, and radiation efficiency was investigated. The soft M-type BaFe9.6Co1.2Ti1.2O19 hexaferrite (Co/Ti-substituted BaM) was synthesized by a combination of ball-milling and two-step sintering processes. Permeability and loss tan δµ of the Co/Ti-substituted BaM were measured to be 4.5 and 0.039 at 200 MHz, respectively. The Wheeler cap method and network analyzer were used to evaluate antenna radiation efficiency and measure return losses, respectively. Our experimental results show that the low-loss Co/Ti-substituted BaM is an excellent soft magnetic material for VHF (very high frequency: 30–300 MHz) miniature antenna applications.

Magnetic properties and ferromagnetic resonance (FMR) frequency of Ni0.7Mn0.3−xCoxFe2O4 ferrites (NiMnCo: x = 0.00, 0.04, 0.06, and 0.10) were controllable with the concentration of cobalt (Co). The measured saturation magnetization remains almost constant at 57 emu/g in the studied range of the Co content. However, the coercivity increased to 72 Oe (x = 0.10) from 12 Oe (x = 0.00). Ferromagnetic resonance frequency increased from 129 MHz to the GHz frequency with increasing the Co content from x = 0.00 to x = 0.10, but the real part of permeability decreased to 1.6 from 16.7. This is because FMR frequency increases with the magnetocrystalline anisotropy (Hk) of the Co according to fr = (γ/2π)Hk. The permeability decreased with the Co content by µ = 1 + (4πMs/Hk). Temperature coefficient, in the range of 20–100 °C, was 0.002 for Ni0.7Mn0.3Fe2O4 (x = 0.00) and 0.008 for Ni0.7Mn0.2Co0.1Fe2O4 (x = 0.10). The results suggest that Ni0.7Mn0.3−xCoxFe2O4 ferrites have excellent temperature stability, and also are...

Low magnetic and dielectric loss Co2Z (Ba3Co2Fe24O41)–glass composite in the frequency range of 1–3 GHz is reported. Co2Z–glass composite was prepared by firing a mixture of 40 h shake-milled Co2Z hexaferrite powder and borosilicate glass at 950 °C for 1 h. The real part of permeability decreased slightly from 2.29 to 1.96 at 2.4 GHz as the glass content increased from 0 to 4 wt. %, but magnetic loss decreased less than 0.02. On the other hand, the real part of permittivity was 7.29 at 0 wt. % and 7.28 at 4 wt. % glass and dielectric loss was less than 0.01 at 2.4 GHz. The 3D peak gain of Co2Z–glass composite chip antenna was measured to be 3.32 dBi at 2.35 GHz. These results imply that the Co2Z–glass composite is an underpinning magnetodielectric material for gigahertz antenna applications.

Single crystals of Zr-substituted Zn-Y (Zr–ZnY; Ba2Zn2ZrxFe12−xO22) were grown from the flux system of BaCO3 and B2O3 by a high temperature slow cooling flux method. X-ray diffraction pattern confirmed the crystal structure with Zn–Y composition. The single crystals were characterized for magnetic and microwave properties. The measured anisotropy field (HA) and the in-plane magnetization (σs) are 13 kOe and 52.0 emu/g, respectively. Ferrimagnetic resonance measurements show 18 Oe of linewidth (ΔH) at 9 GHz. The combination of low ΔH with a high HA in Zr–ZnY hexaferrite is suitable for microwave devices, which can operate with low external biasing field.

This paper deals with analytical approach of operational power defined as load power and rotor loss represented as eddy current loss for applying a permanent magnet (PM) synchronous motor/generator to the high-power flywheel energy storage system. The used model is composed of a double-sided Halbach magnetized PM rotor and coreless three-phase winding stator. For one such motor/generator structure, we provide the magnetic field and eddy current with space and time harmonics via magnetic vector potential in two-dimensional (2D) polar coordinate system. From these, the operational power is estimated by backelectromotive force according to the PM rotor speed, and the rotor loss is also calculated from Poynting theorem.

This paper presents analytical methods to predict the magnetic field distribution, electrical parameters, and output characteristics of a high speed synchronous generator equipped with surface-mounted permanent magnet. In order to analyze the magnetic field distribution and to estimate the electrical parameters, electromagnetic transfer relation (TR) theorem is employed. Moreover, output characteristics for variable resistive load and the operating speed are also obtained by solving the permanent magnet machine’s equivalent circuit equation. The analytical results are validated extensively by nonlinear finite element analysis and experimental results.

In this paper, the rotor losses in the high-speed permanent magnet (PM) synchronous motor are discussed. In particular, the influence of different load conditions is highlighted in developed PM synchronous motor. On the basis of analytical field analysis, two-dimensional fast Fourier transformation, and the Poynting theorem, the flux harmonics and rotor losses are predicted and validated by finite element method. Moreover, the difference of rotor losses between the motor with rated- and overload conditions is made quantitatively clear in this work.

We report on the tetracene-based photo-thin-film transistors (photo-TFTs) which adopt thin poly-4-vinylphenol (PVP)/aluminum oxide (AlOx) bilayer for a gate dielectric and two different source/drain (S∕D) electrodes: semitransparent NiOx and Au. Our tetracene-based TFT with NiOx S∕D electrode exhibited quite good field effect mobility (μ=∼0.23cm2∕Vs), high on/off current ratio (Ion∕Ioff) of ∼105, and good photo-to-dark current ratio (Iph∕Idark=∼104) under an ultraviolet (364nm) illumination while that with Au S∕D electrodes showed much lower device performance (μ=∼0.08cm2∕Vs, Ion∕Ioff=∼104, and Iph∕Idark=∼20), although the both TFTs operated at a low voltage of −8V. With the hole-injection and light-reception advantages of NiOx electrode, our tetracene photo-TFT demonstrated good dynamic optical gating.

This paper presents the practical parameter estimation for a slotless air-cored permanent magnet linear synchronous motor (PMLSM) using an analytical method and experiment. In the analytical method, the linkage flux is calculated through the generalized magnetic vector potential obtained by the space harmonics and transfer relation with each region of permanent magnet (PM) mover, air gap, and winding stator. This linkage flux is used to estimate the dynamic parameters such as magnetization inductance, backemf, and thrust constant. Also, the resistance and self-inductance with one phase are obtained by the experiment. Therefore, dynamic simulation of a linear synchronous motor composed of dynamic parameters is performed by the nonrotating (d-q) voltage equation. In good agreement with the estimated parameter values, the experimental results confirm the validity of the analysis method and simulation.