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High density sintered Sm(Fe0.8Co0.2)11Ti bulk magnets were successfully produced using a newly developed high pressure pressing fabrication method. The purity of the hard magnetic ThMn12 phase in the bulk magnet reached to higher than 97 wt.%. The phase transformation behavior from amorphous to ThMn12 phase during heat treatment was systematically investigated by transmission electron microscopy. The remanent magnetization and maximum energy product of a bulk magnet were 96.0 emu/g and 12.22 MGOe, respectively. To the best of our knowledge, the achieved maximum energy product is the highest among all the SmFe12-based bulk magnets reported.

Freestanding graphene on a trench has been fabricated extensively using a transfer process of chemical vapor deposition grown graphene. Here, we demonstrate that freestanding graphene can be grown directly on a trench without a transfer process. A shallow trench was made on a 6H–SiC(0001) wafer using a focused ion beam lithography. The shallow trench was heated to a high temperature under Ar atmosphere. The heat treatment made the shallow trench become deeper and wider. Subsequently, epitaxial graphene was floating on the trench, resulting in freestanding graphene, where underlying bulk SiC was self-etched after the growth of epitaxial graphene. The freestanding graphene on a trench was characterized using Raman spectroscopy and atomic force microscopy. Such freestanding graphene writing can be applied to semiconductor fabrication process of freestanding graphene devices without a transfer process.

Various methods have been suggested to realize freestanding or suspended graphene, which is expected to exhibit the intrinsic properties of graphene. However, in previously reported methods, multiple-step processes have been applied to produce freestanding graphene on a substrate. Here, we demonstrate that quasifreestanding graphene on a substrate can be realized through a simple single-step process. In this experiment, self-etching of nano-scale SiC steps of 8° off-axis vicinal SiC contributed to the formation of quasifreestanding graphene on an Si-faced SiC wafer, which was confirmed using low-energy electron diffraction, Raman spectroscopy, scanning electron microscopy and two-probe resistance measurements. Such a single-step technique for the growth of quasifreestanding graphene could pave the way towards graphene-based silicon-carbide micro-electronics.

The Sm(Fe0.8Co0.2)11Ti were prepared by using arc-melting and melt spinning methods, and their crystallographic and magnetic properties were analyzed by using XRD, VSM, and Mossbauer spectrometer. From the refined XRD patterns, Sm(Fe0.8Co0.2)11Ti sample exhibited tetragonal structure with the space group I4/mmm and it was confirmed that Ti and Co atom were found to be located at 8i and 8f-site, respectively. The Mossbauer spectra of the samples were obtained at 295 K, and investigated the hyperfine interaction and site occupancy in Sm(Fe0.8Co0.2)11Ti sample. From the hysteresis curves up to 20 kOe at 295 K, the magnetization at 20 kOe (M20 kOe) and intrinsic coercivity (Hc) of the sample showed the highest values of M20 kOe = 107.43 emu/g and Hc = 2399.3 Oe, when annealed at 800 °C for 4 h.

The isotropic nanoparticles (NPs) and anisotropic bulk samples of MnBi were prepared from Mn NPs by using zero-field and field-assisted reactive sintering, respectively. The MnBi NPs are irregular in shape with size d

Rare-earth-free permanent magnets have attracted considerable attention due to their favorable properties and applicability for cost-effective, high-efficiency, and sustainable energy devices. However, the magnetic field annealing process, which enhances the performance of permanent magnets, needs to be optimized for different magnetic fields and phases. Therefore, we investigated the effect of composition on the crystallization of amorphous MnBi to the ferromagnetic low-temperature phase (LTP). The optimal compositions and conditions were applied to magnetic field annealing under 2.5 T for elemental Mg- and Sb/Mg pair-substituted MnBi. The optimum MnBi composition for the highest purity LTP was determined to be Mn56Bi44, and its maximum energy product, (BH)max, was 5.62 MGOe. The Mg-substituted MnBi exhibited enhanced squareness (Mr/Ms), coercivity (Hc), and (BH)max values up to 0.8, 9659 Oe, and 5.64 MGOe, respectively, whereas the same values for the Sb/Mg pair-substituted MnBi were 0.76, 7038 Oe, and 5.60 MGOe, respectively. The substitution effects were also investigated using first-principles calculations. The density of states and total magnetic moments of Mn16Bi15Mg and Mn16Bi15Sb were similar to those of pure Mn16Bi16. Conversely, the Sb-substituted MnBi resulted in a dramatic enhancement in the anisotropy constant (K) from a small negative value (&minus, 0.85 MJ/m3) to a large positive value (6.042 MJ/m3).

The ferromagnetic MnAl-C powders were prepared by using a one-step solid-state reaction method starting from Mn micro-/nano-particles and Al/C micropowders. The bulk MnAl-C with enhanced coercivity was prepared by high-pressure compaction of these MnAl-C powders. The grain size of the τ-phase was significantly reduced during high-pressure compaction, which may also result in a decomposition of the τ-MnAl. Carbon element stabilizes the τ-phase under both ambient and high pressures. The annealing temperature and time intervals are crucial for the preparation of high purity τ-phase samples. The MnAl-C with smaller particle size were produced from Mn nanoparticles. In comparison with the samples prepared from Mn micropowders, the product prepared from Mn nanoparticles shows lower purity, owing to the surface oxidation of the precursor nanoparticles. After high pressure compaction, the coercivities of the bulk MnAl and MnAl-C were increased from 0.05 T and 0.08 T to 0.39 T and 0.22 T, respectively. The room temperature magnetization of the MnAl-C sample at 4 T reached up to 95 Am2/kg.

Ferromagnetic τ-phase Mn54Al46C2.44 particles were synthesized, and its composites with commercial Sm2Fe17N3 and synthesized Fe65Co35 powders were fabricated. Smaller grain size than the single domain size of the Mn54Al46C2.44 without obvious grain boundaries and secondary phases is the origin for the low intrinsic coercivity. It was confirmed that the magnetic properties of the Mn54Al46C2.44 can be enhanced by magnetic exchange coupling with the hard magnetic Sm2Fe17N3 and soft magnetic Fe65Co35. The high degrees of the exchange coupling were verified by calculating first derivative curves. Thermo-magnetic stabilities of the composites from 100 to 400 K were measured and compared. It was demonstrated that the Mn54Al46C2.44 based composites containing Sm2Fe17N3 and Fe65Co35 could be promising candidates for future permanent magnetic materials with the proper control of purity, magnetic properties, etc.

Bulk MnAl-C magnets were prepared via high-pressure compaction of melt-spun ribbons. The e → τ phase transformation (PT) in the melt-spun MnAl and MnAlC ribbons occurs mainly via the massive mode, whereas the displacive mode is not prominent. The massive PT temperatures of the melt–spun MnAl and MnAlC ribbons were measured to be in the range 660–739 K and 700–758 K, respectively. The PT temperatures of the melt-spun MnAlC ribbons are lower than those of water–quenched MnAlC. The annealing process for producing τ-phase from e-phase was optimized based on the measured PT temperature range. As a result, no decomposition of the metastable e/τ-phase MnAl and MnAlC were observed during the optimized high temperature annealing. High-purity τ-phase MnAlC ribbons with high magnetization (122 Am2/kg at 8 T) and low coercivity (0.13 T) were obtained. The coercivity of the bulk MnAlC obtained by high-pressure compaction was significantly enhanced and reached 0.38 T partially due to the grain refinement of the sample during high-pressure deformation.

The low temperature phase Mn55Bi45-xGax (x = 0, 1, 3, 5, and 10) alloys were prepared by induction melting process with subsequent low temperature annealing. The effects of Ga-doping on the crystal structure and magnetic properties of the alloys were systematically studied. The room temperature coercivities of Mn55Bi45-xGax after ball milling increased from 1.43 T for x = 0 to 1.66 T for x = 5, while the saturation magnetization decreased from 60.7 Am2/kg (x = 0) to 45.1 Am2/kg (x = 5). The maximum energy product (BH)max of Mn55Bi44Ga powders reached 7.87 MGOe. The Curie temperature of the Mn55Bi45-xGax alloys increased from 633 K to 658 K with increasing Ga concentration in the range of 0 ≤ x ≤ 5.

The temperature for phase transformation of e → τ in Mn 54 Al 46 C x (hereafter denoted by MnAlC x , x = 0–5) alloys was systematically studied by using the traditional thermal analysis method and a more precise magnetic measurement method developed in this work. The effect of carbon content and cold-rolling on the magnetic properties of the MnAlC x alloys was studied. The onset temperature of massive growth of τ- from e-phase increases with increasing carbon content in MnAlC x . The carbon content has little effect on the onset temperature of displacive growth of e → τ but has substantial effect on the displacive growth rate at certain temperature. Pure τ-MnAlC x with varied x was obtained by annealing the e-phase at optimum temperatures determined by our method. The Curie temperature of the MnAlC x decreases significantly first and then increases slightly with increasing carbon content. The coercivity and the remanent magnetization of the as-prepared τ-MnAlC x increase with increasing x first and become stable at x > 3 and x > 4, respectively. A cold-rolling method was introduced in this work to enhance the magnetic properties of τ-MnAlC x . The coercivity and remanent magnetization of the τ-MnAl after cold-rolling were enhanced up to 4.3 times and 3.3 times, respectively. The coercivity of the cold-rolled τ-MnAlC x decreases with increasing x and becomes stable when x > 2. The remanent magnetization and saturation magnetization of the cold-rolled τ-MnAlC x vary little with x .

We report a simple wireless power charging (WPC) antenna system (50 mm $\times40$ mm $\times0.1$ mm) for use in simulating power transfer efficiency ( $\eta $ ) with and without ferrite and a metallic object (battery case), thereby identifying suitable magnetic parameters and ferrite sheet thickness. The simulation results suggest that magnetic loss tangent (tan $\delta _{\mu }$ ) and permeability ( $\mu '$ ) need to be less than 0.05 and higher than 125 at 13.56 MHz, respectively, to achieve at least 75% of the transfer efficiency ( $\eta _{\mathrm {max}}$ ) of the WPC antenna without ferrite and the metallic object. Accordingly, we have fabricated Ni x Zn0.85– x Cu0.15Fe2O4 (x = 0.32 – 0.38) spinel ferrites using a one-step sintering process and obtained relatively high $\mu '$ of 169 and low tan $\delta _{\mu }$ of 0.1 with a nickel (Ni) concentration of 0.38. This magnetic loss is still too high to achieve 75% of the $\eta _{\mathrm {max}}$ value. In order to further reduce the magnetic loss, a two-step sintering process was used. The two-step sintered Ni0.38Zn0.47Cu0.15Fe2O4 shows $\mu '$ of 132 and a tan $\delta _{\mu }$ of 0.03 at 13.56 MHz, respectively. Therefore, this ferrite meets criteria identified by the transfer efficiency simulation and is a good candidate for 13.56-MHz wireless power transfer charging antenna system. In addition, our designed WPC system is capable of evaluating other magnetic materials that are suitable for WPC antenna applications.

We have calculated electronic structures of Mn4C using first-principles calculations based on density functional theory (DFT) within the Perdew Burke Ernzerhof-generalized gradient approximation (PBE-GGA). The calculated band structures and density of states (DOS) indicate that stability of cubic perovskite-type crystal structured Mn4C is originated from p-d hybridization between Mnb and C and d-d hybridization between Mna and Mnb sublattices. The mean field approximation (MFA) resulted in the Neel temperature (TN) of 879 K which is in close agreement with experimental TN. The temperature dependence of magnetic moments of Mna and Mnb sublattices were also calculated using the Brillouin function to investigate the origin of unusual linearly increasing magnetization below 400 K. It was found that the increasing magnetization is originated from strong mutual interdependence of more or less linearly decreasing magnetic moment of Mna and stationary magnetic moment of Mnb below 400 K.

In the semiconductor etch process, as the critical dimension (CD) decreases and the difficulty of the process control increases, in-situ and real-time etch profile monitoring becomes important. It leads to the development of virtual metrology (VM) technology, one of the measurement and inspection (MI) technology that predicts the etch profile during the process. Recently, VM to predict the etch depth using plasma information (PI) variables and the etch process data based on the statistical regression method had been developed and demonstrated high performance. In this study, VM using PI variables, named PI-VM, was extended to monitor the etch profile and investigated the role of PI variables and features of PI-VM. PI variables are obtained through analysis on optical emission spectrum data. The features in PI-VM are investigated in terms of plasma physics and etch kinetics. The PI-VM is developed to monitor the etch depth, bowing CD, etch depth times bowing CD (rectangular model), and etch area model (non-rectangular model). PI-VM for etch depth and bowing CD showed high prediction accuracy of R-square value (R2) 0.8 or higher. The rectangular and non-rectangular etch area model PI-VM showed prediction accuracy R2 of 0.78 and 0.49, respectively. The first trial of virtual metrology to monitor the etch profile will contribute to the development of the etch profile control technology.

We report a low magnetic loss Ba3Co2Fe24O41 (Co2Z) hexaferrite for use in gigahertz (GHz) antennas. Acid-etching was very effective in removal of unwanted Y-type hexaferrite (Ba2Co2Fe12O22) from calcined Co2Z powder. It is found that the calcined and acid etched (AE) Co2Z hexaferrite shows a low magnetic loss tangent (tan δμ) of 0.012 and 0.037 at 1 and 2 GHz, respectively. These low tan δμ are attributed to removal of Y-type hexaferrite, which possesses a lower anisotropy field (Hk) than W-type hexaferrite (BaCo2Fe16O27). The figure of merit (FOM) of the AE Co2Z hexaferrite is 141.7 and 48.7 at 1 and 2 GHz, respectively. These FOM are much higher than the FOM of previously reported low-loss magnetic materials. Therefore, the AE Co2Z hexaferrite can be a good candidate for GHz antenna application in the ultra-high frequency (UHF) band.

We have developed a miniaturized implantable ferrite antenna, operating in the industrial, scientific, and medical band (2.4–2.5 GHz). The dip-coated NiCo ferrite films effectively reduces the antenna resonance by 110 MHz, with a 4.2 dB reflection coefficient improvement as compared with an antenna without ferrite. The ferrite antenna also reveals a 6 dBi and 35 MHz improvement in realized gain and −10 dB bandwidth, respectively, at resonance. The effects of ferrite film loading on antenna performance are further investigated with parametric simulations and experimental comparisons.© 2016 Wiley Periodicals, Inc. Microwave Opt Technol Lett 58:2745–2749, 2016

For transition metal dichalcogenides, the fluctuation of the channel current due to charged impurities is attributed to a large surface area and a thickness of a few nanometers. To investigate current variance at the interface of transistors, we obtain the low-frequency (LF) noise features of MoTe2 multilayer field-effect transistors with different dielectric environments. The LF noise properties are analyzed using the combined carrier mobility and carrier number fluctuation model which is additionally parametrized with an interfacial Coulomb-scattering parameter (α) that varies as a function of the accumulated carrier density (Nacc) and the location of the active channel layer of MoTe2. Our model shows good agreement with the current power spectral density (PSD) of MoTe2 devices from a low to high current range and indicates that the parameter α exhibits a stronger dependence on Nacc with an exponent -γ of -1.18 to approximately -1.64 for MoTe2 devices, compared with -0.5 for Si devices. The raised Coulomb scattering of the carriers, particularly for a low-current regime, is considered to be caused by the unique traits of layered semiconductors such as interlayer coupling and the charge distribution strongly affected by the device structure under a gate bias, which completely change the charge screening effect in MoTe2 multilayer. Comprehensive static and LF noise analyses of MoTe2 devices with our combined model reveal that a chemical-vapor deposited h-BN monolayer underneath MoTe2 channel and the Al2O3 passivation layer have a dissimilar contribution to the reduction of current fluctuation. The three-fold enhanced carrier mobility due to the h-BN is from the weakened carrier scattering at the gate dielectric interface and the additional 30% increase in carrier mobility by Al2O3 passivation is due to the reduced interface traps.

We have calculated the electronic structures of FePt and Fe0.9375Mn0.0625Pt using first principle calculations based on density functional theory within the local-spin-density approximation (LSDA). The Curie temperature ( $T_{c})$ was calculated by a simple model based on the mean field approximation. A supercell structure, containing eight unit cells, was used to calculate the density of states. The saturation magnetization ( $M_{s})$ and magnetocrystalline anisotropy constant ( $K$ ) at 0 K, and $T_{c}$ for Fe0.9375Mn0.0625Pt were calculated to be 942 emu/cm3, $8.24 \times 10^{6}$ J/ $\text{m}^{3}$ , and 590 K, respectively. The temperature-dependent $M(T)$ and $K(T)$ of Fe0.9375Mn0.0625Pt were calculated using the Brillouin function and Callen–Callen experimental relation, respectively, to obtain an $M_{s}$ and a $K$ of 822 emu/cm3 and $6.29 \times 10^{6}$ J/ $\text{m}^{3}$ at 300 K, respectively. These values meet the required $M_{s}$ and $K$ of 800 emu/cm3 and $5.00 \times 10^{6}$ J/ $\text{m}^{3}$ for achieving 4 Tb/in2 heat-assisted magnetic recording media (HAMR).

Mn54Al46C2.44 alloy as new permanent magnetic materials was produced by induction melting, and its powders were produced by low energy ball milling. The milled powders were annealed to study the effect on their phase transformation and magnetic properties. The powder undergoes massive phase transformation at an annealing temperature of 450 °C, and reaches the maximum saturation magnetization ( $\sigma _{s})$ when annealed at 480 °C for 5 min, while its intrinsic coercivity ( $H_{\mathrm {ci}})$ continually increases with the temperature. The initial increment of the $H_{\mathrm {ci}}$ is due to the phase transformation from paramagnetic $\varepsilon $ -phase to ferromagnetic $\tau $ -phase and remaining $\varepsilon $ -phase and formation of secondary phases, such as nonmagnetic $\gamma _{2}$ - and $\beta $ -phases, that acts as pinning points for the domain walls. The next one is caused by the increasing percentage of the secondary phases that decreases $\sigma _{s}$ . Based on the delta $M$ analysis, it can be verified that the increased $H_{\mathrm {ci}}$ with increasing secondary phases when annealed at temperatures above 480 °C is due to the decreasing magnetization.

In this study, the effects of NaOH and precursor concentration on the particle size and magnetic properties of FeCo nanoparticles are investigated. Results suggest that an optimized ratio of NaOH molar concentration [OH] to precursor molar concentration [M] is required to obtain a small particle size, high saturation magnetization, and low coercivity. When the [OH]/[M] ratio was greater than 40, the FeCo nanoparticles aggregated, whereas when the [OH]/[M] ratio was less than 20, FeCo + CoFe2O4 nanoparticles were obtained due to unstable reduction reactions. When [OH]/[M] was 40, the 387 nm FeCo nanoparticles showed the highest saturation magnetization and lowest coercivity, which are the best conditions for achieving high permeability. In contrast, the complex permeability of the 173 nm FeCo nanoparticles was higher than that of the 387 nm FeCo nanoparticles owing to the decrease in the demagnetization effect in the high frequency band. This confirmed that the particle size had a greater effect on the complex permeability than that on the saturation magnetization and coercivity in GHz ranges.

The magnetization of most materials decreases with increasing temperature due to thermal deterioration of magnetic ordering. Here, we show that Mn4C phase can compensate the magnetization loss due to thermal agitation. The Mn&ndash, C nanoparticles containing ferrimagnetic Mn4C and other Mn&ndash, C/Mn-O phases were prepared by using the traditional arc-discharge method. A positive temperature coefficient of magnetization (~0.0026 Am2 kg&minus, 1 K&minus, 1) and an exchange bias up to 0.05 T were observed in the samples. We ascribe the exchange bias to the co-existence of ferrimagnetic Mn4C/Mn3O4 and antiferromagnetic &alpha, Mn(C)/MnO phases. The positive temperature coefficient of magnetization of the samples was ascribed to the presence of Mn4C phase, which is considered as a N&eacute, el&rsquo, s P-type ferrimagnet.

The Mn–Bi nanoparticles were prepared by using laser ablation and arc-discharge method, respectively. The arc-evaporated Mn–Bi nanoparticles exhibit ideal spherical shape with size in the range of several tens of nanometers to several hundreds of nanometers, whereas the laser-ablated Mn–Bi nanoparticles exhibit an irregular shape with smaller particle size. The Bi content in the arc-evaporated Mn–Bi nanoparticles was significantly enhanced compared to that of the Mn–Bi master alloys because of the higher vapor pressure of Bi than that of Mn in the melt. The Mn content in the arc-evaporated Mn–Bi nanoparticles increases with increasing Mn content in the master alloys. However, the Bi and Mn contents in the laser-ablated nanoparticles deviate little from that of the master alloys because of the highly localized molten pool of MnBi over the surface of the master alloys and the higher temperature reached using laser beams. The fraction of the low-temperature phase MnBi in the nanoparticles prepared by both methods increases with increasing annealing temperature and time. The laser ablation method is more effective in controlling the composition of the products. The coercivities of the arc-evaporated and laser-ablated Mn–Bi nanoparticles after annealing reached up to 0.65 and 0.8 T, respectively. The saturation magnetization of the annealed laser-ablated Mn–Bi nanoparticles reaches up to 51.6 Am2/kg.

We report on the X-ray diffraction data and unit-cell parameters of Mn4C, which has a cubic perovskite-type structure with a = 3.8726 Å and unit-cell volume V = 58.1 Å3. The measured lines were indexed and are consistent with the space group $ Pm { \bar {\it 3}} m$ (No. 221).

M-type strontium ferrite (SrFe12O19: SrM) with two different shapes were synthesized by a simple and benign process. One is peanut-like shape, and the other is hexagonal platelet. These shapes were controlled by the shape and size of precursor Fe3O4 particles. A mixture of submicron- or nanometer-sized Fe3O4 particles and SrCO3 nanoparticles was calcined to transform to SrM, followed by acid-washing to remove secondary phase from SrM particles. Static magnetic properties, magnetic interactions, and thermomagnetic stability of the SrM particles were studied. The measured saturation magnetization and intrinsic coercivity are 74.2 emu/g and 4431 Oe, respectively, for the peanut-like SrM particles and 73.6 emu/g and 5360 Oe for the hexagonal SrM platelets. The saturation magnetization is close to the theoretical value of 76 emu/g. Both types of SrM show dipolar interactions and good thermomagnetic stability, i.e. α = Δσs/σs = −0.16%/K and β = ΔHci/Hci = 0.15%/K for the peanut-like SrM particles and α = −0.12%/K and β = 0.12%/K for the hexagonal SrM platelets. The temperature coefficient of intrinsic coercivity (β) is positive and magnetization still remains high at 400 K; 60 emu/g for the hexagonal SrM platelets and 50 emu/g for the peanut-like SrM particles.

Planar gigahertz (GHz) inductors were fabricated based on high crystalline-anisotropy Zn0.13Co0.04Ni0.63Fe2.2O4 (Zn-Co-Ni ferrite) and Ba3Co2Fe24O41 (Co2Z hexaferrite) and characterized for inductance (L) and quality (Q) factor. The planar ferrite inductors show an L of 4.5 nH (Zn-Co-Ni), 5.6 nH (Zn-Co-Ni + low Hk and fFMR Co2Z:), and 4.8 nH (Zn-Co-Ni + high Hk and fFMR Co2Z:) at 2GHz. The corresponding L-densities are 18.0, 22.4, and 19.2 nH/mm2, which are greater than 16.8 nH/mm2 of the air-core inductor. With respect to the Q factor, the air-core and ferrite inductors exhibit Q factors of 6.7 (air-core), 4.8 (Zn-Co-Ni), 2.8 (Zn-Co-Ni + low Hk Co2Z), and 4.0 (Zn-Co-Ni + high Hk Co2Z) at 2GHz. The tan δμ of the ferrites caused a reduction in the Q factor. Nevertheless, the high Hk and fFMR Co2Z ferrite inductor demonstrates a higher Q factor than that of the low Hk and fFMR Co2Z inductor. It is, therefore, suggested that high resistivity, anisotropy, magnetization ferrite can produce large L density and Q factor GHz inductors.

The phase transformation in two modes, including both displacive and massive growth of τ-phase from ε-MnAl(C), was observed by in situ transmission electron microscopy. The exact temperature range for different phase transformation modes was determined by magnetic measurements. The displacive growth of ε→τ in Mn54Al46 (or Mn54Al46C2.44) occurs at temperatures below 650 K (or 766 K), above which both modes coexist. One-third or less of the ε-phase can be transformed into τ-phase via displacive mode while the remaining two-thirds or more via massive mode. In bulk τ-phase, most τ-nanocrystals formed via displacive mode are distributed in the matrix of large τ-grains that formed via massive mode. The typical massive growth rate of the τ-phase is 8–60 nm/s, while the displacive growth rate is low. A more complete understanding of the ε→τ phase transformations in the MnAl-based magnets was provided in this work, based on which the annealing process for ε→τ was optimized and thus high purity τ-phase with high saturation magnetization was obtained.

We present a simple analytical model to estimate the magnetization (σs) and intrinsic coercivity (Hci) of a hard/soft nanocomposite magnet using the mass fraction. Previously proposed models are based on the volume fraction of the hard phase of the composite. However, it is difficult to measure the volume of the hard or soft phase material of a composite. We synthesized Sm2Co7/Fe-Co, MnAl/Fe-Co, MnBi/Fe-Co, and BaFe12O19/Fe-Co composites for characterization of their σs and Hci. The experimental results are in good agreement with the present model. Therefore, this analytical model can be extended to predict the maximum energy product (BH)max of hard/soft composite.

High coercivity B-N-doped MnAl alloys were prepared by the traditional induction melting, high temperature homogenization, water-quenching, post-annealing, and severe plastic deformation process. The massive phase transformation of the e→τ in the B-N-doped e-MnAl occurs at the temperatures above 680 K and accomplishes at 760 K, both of which are slightly higher than those of the e-MnAl without elemental doping. The Currie point of the B-N-doped τ-MnAl is measured to be 620 K, which is lower than that of the doping-free τ-MnAl. High-pressure torsion was employed to decrease the crystal size and increase the coercivity of samples. A coercivity up to 0.54 T was achieved in the B/N doped MnAl bulk sample after severe plastic deformation under 6 GPa. The aging processing on the severely deformed samples enhances the remanent magnetization significantly and decreases the coercivity slightly. Our work shows that the high-pressure torsion process is effective in developing coercivity in MnAl-based bulk magnet.

Nonmagnetic phase assisted low temperature phase MnBi bulk magnetic materials, i.e., MnBi/NaCl and MnBi/C magnets, were fabricated by hot pressing mixtures of MnBi and NaCl or C powders. The effects of nonmagnetic NaCl or C on the magnetic and physical properties of the MnBi bulks were investigated in detail. Identifications of phase stability and decomposition rate during the mixing and hot pressing processes were analyzed using the Rietveld refinement method. It was found that the coercivities (Hc) of the bulk magnets significantly increase with increasing content of NaCl or C: Hc of the MnBi bulks with NaCl of 5 wt. % and C of 5 wt. % reach 9041 Oe and 7054 Oe, respectively, which are higher than the pure MnBi bulk of 6272 Oe. This means that the addition of a small amount of NaCl and C in the MnBi bulks could be one of the promising routes to enhance their magnetic properties.Nonmagnetic phase assisted low temperature phase MnBi bulk magnetic materials, i.e., MnBi/NaCl and MnBi/C magnets, were fabricated by hot pressing mixtures of MnBi and NaCl or C powders. The effects of nonmagnetic NaCl or C on the magnetic and physical properties of the MnBi bulks were investigated in detail. Identifications of phase stability and decomposition rate during the mixing and hot pressing processes were analyzed using the Rietveld refinement method. It was found that the coercivities (Hc) of the bulk magnets significantly increase with increasing content of NaCl or C: Hc of the MnBi bulks with NaCl of 5 wt. % and C of 5 wt. % reach 9041 Oe and 7054 Oe, respectively, which are higher than the pure MnBi bulk of 6272 Oe. This means that the addition of a small amount of NaCl and C in the MnBi bulks could be one of the promising routes to enhance their magnetic properties.

We report electronic structures of M-type SrFe 12 O 19 and La 3+ - Co 2+ pair substituted Sr 1-x La x Fe 1-x Co x O 19 ferrites (x = 0.1 - 0.5). First-principles calculations were performed on the ferrites to calculate electronic structures. The substitution of La 3+ - Co 2+ in the 2d and 2a sites decreased the lattice constants and total magnetic moment per unit cell. The moments at 2b, 12k, 4 f1, and 4 f2 sites are not affected by the substitution. Nonsubstituted SrFe 12 O 19 is a semiconductor, but becomes half-metallic when La 3+ and Co 2+ are substituted in the 2d and 2a sites, respectively.

A graphene Hall element (GHE) is an optimal system for a magnetic sensor because of its perfect two-dimensional (2-D) structure, high carrier mobility, and widely tunable carrier concentration. Even though several proof-of-concept devices have been proposed, manufacturing them by mechanical exfoliation of 2-D material or electron-beam lithography is of limited feasibility. Here, we demonstrate a high quality GHE array having a graphene on hexagonal-BN (h-BN) heterostructure, fabricated by photolithography and large-area 2-D materials grown by chemical vapor deposition techniques. A superior performance of GHE was achieved with the help of a bottom h-BN layer, and showed a maximum current-normalized sensitivity of 1986 V/AT, a minimum magnetic resolution of 0.5 mG/Hz(0.5) at f = 300 Hz, and an effective dynamic range larger than 74 dB. Furthermore, on the basis of a thorough understanding of the shift of charge neutrality point depending on various parameters, an analytical model that predicts the magnetic sensor operation of a GHE from its transconductance data without magnetic field is proposed, simplifying the evaluation of each GHE design. These results demonstrate the feasibility of this highly performing graphene device using large-scale manufacturing-friendly fabrication methods.

The effects of elemental doping of Si and Fe on the ε→τ phase transformation and the magnetic properties of MnAl were studied. The magnetic powders of Si- and Fe-doped MnAl were prepared by using induction melting followed by water-quenching, annealing, and salt-assisted ball-milling. The Fe-doped MnAl powders are mainly composed of the L10-structured τ-phase, while the Si-doped MnAl are composed of τ-phase and a small fraction of γ2- and β-phases. A unique thin leaves-like morphology with thickness of several tens of nanometers and diameter size up to 500 nm were observed in the Si-doped MnAl powders. The Fe-doped MnAl powders show irregular shape with much larger dimensions in the range from several to 10 μm. The morphology difference of the samples was ascribed to the variation of the mechanical properties affected by different doping elements. The phase transformation temperatures of the ε-phase of the samples were measured. The doping of Fe decreases the onset temperature of the massive phase transformation in MnAl, while the Si-doping increases the massive phase transformation temperature. Both Fe and Si increase the Curie temperature of MnAl. A substantially enhanced coercivity up to 0.45 T and 0.42 T were observed in the ball-milled MnAl powders doped with Si and Fe, respectively.

Thousands of high-performance 2D metal-oxide-semiconductor field effect transistors (MOSFETs) were fabricated on wafer-scale chemical vapor deposited MoS2 with fully-CMOS-compatible processes such as photolithography and aluminum metallurgy. The yield was greater than 50% in terms of effective gate control with less-than-10 V threshold voltage, even for MOSFETs having deep-submicron gate length. The large number of fabricated MOSFETs allowed statistics to be gathered and the main yield limiter to be attributed to the weak adhesion between the transferred MoS2 and the substrate. With cut-off frequencies approaching the gigahertz range, the performances of the MOSFETs were comparable to that of state-of-the-art MoS2 MOSFETs, whether the MoS2 was grown by a thin-film process or exfoliated from a bulk crystal.

(94-x)(Na1/2Bi1/2)TiO3-6BaTiO(3)-x(K1/2Na1/2)NbO3 (NBT-6BT-xKNN) piezoelectric ceramics have notable potential for replacing lead containing piezoelectric ceramics in actuator applications due to their exceptionally large strain. However, a high electric field for producing a large strain and a large hysteresis are critical issues that should be resolved for practical actuator applications. In an attempt to address these issues and optimize the piezoelectric performance, we fabricated NBT-6BT-xKNN (x = 0 - 5) piezoelectric single crystals with a size of 8 x 8x 10 mm by the solid-state single crystal growth method and systematically measured their electrical properties. With increased addition of KNN to replace NBT, the ferroelectricity and piezoelectricity of the fabricated [001]NBT-6BT-xKNN single crystals decreased, but their unipolar strain and hysteresis were considerably improved. For NBT-6BT-5KNN single crystals, the largest maximum strain (S-max) was 0.57% at 6 kV/mm, showing a converse piezoelectric constant (S-max/E-max) of 950 pm/V, and their hysteresis in the unipolar S-E curve was 12% at 6kV/mm, which would be appropriate for some actuator applications. Our results demonstrate the applicability of the produced single crystals as lead-free piezoelectric actuator components. (C) 2016 Author(s). All article content, except where otherwise noted, is licensed under a Creative Commons Attribution 3.0 Unported License.

We investigated the effect of substitution of various ions at the Fe sites on magnetic properties of strontium hexaferrite (SrFe12O19) using first principles method based on density functional theory. The site occupancies of substituted atoms were estimated by calculating the substitution energies of different configurations. The formation probabilities of configurations were used to calculate magnetic properties of substituted strontium hexaferrite. A total of 21 elements (M) were screened for their possible substitution in strontium hexaferrite, SrFe12−xMxO19 with x = 0.5. In each case the site preference of the substituted atom and the magnetic properties were calculated. We found that Bi, Sb, Sn, and Sc can effectively increase the magnetization and P, Co, Al, Ga, and Ti can enhance the anisotropy field when substituted into strontium hexaferrite.

The correlation between the channel thickness and the carrier mobility is investigated by conducting static and low frequency (LF) noise characterization for ambipolar carriers in multilayer MoTe2 transistors. For channel thicknesses in the range of 5–15 nm, both the low-field carrier mobility and the Coulomb-scattering-limited carrier mobility (μC) are maximal at a thickness of ∼10 nm. For LF noise, the interplay of interface trap density (NST), which was minimal at ∼10 nm, and the interfacial Coulomb scattering parameter (αSC), which decreased up to 10 nm and saturated above 10 nm, explained the mobility (μC) peaked near 10 nm by the carrier fluctuation and charge distribution.

Magnetically exchange coupled SrFe12O19/Fe-Co composites with different mass percentage of Fe-Co were synthesized through an ex situ process. The morphology, magnetic properties, and crystallization of SrFe12O19/Fe-Co composites were investigated. Lower mass percentage of Fe-Co presented an even distribution of Fe-Co nanoparticles on the surface of SrFe12O19, and effective magnetic exchange coupling between Fe-Co and SrFe12O19. Higher mass percentage of Fe-Co leads to an agglomeration of Fe-Co nanoparticles on SrFe12O19 surface, and a weak magnetic exchange coupling between Fe-Co and SrFe12O19. This ex situ process proposed a new method to synthesize magnetically exchange coupled SrFe12O19/Fe-Co core/shell composites with precise control of the magnetic properties. This method can also be potentially used for other hard/soft magnetic composite synthesis.

We have calculated the electronic structure of MnB using first-principles calculations based on the density functional theory within the local-spin-density approximation. The temperature dependence of saturation magnetization [Ms(T)] was calculated by mean field approximation. The calculated density of states (DOS) shows that the energy region near the Fermi energy (EF) is mostly attributed to the d bands of Mn. The saturation magnetizations (Ms) of MnB were calculated to be 964.5 emu/cm3 (1.21 T) at 0 K and 859.3 emu/cm3 (1.08 T) at 300 K. The calculated Ms at 300 K is in good agreement with experimental Ms of 851.5 emu/cm3.

We have calculated electronic structures of nanocrystalline Fe90−xCuxSi10−yBy using first principles calculations based on density functional theory (DFT) to obtain saturation magnetic flux density (Bs). The Bs of crystalline (Fe3Si) and amorphous (Fe-B) phases in Fe90−xCuxSi10−yBy were separately calculated, and the total Bs of Fe90−xCuxSi10−yBy was derived by the summation of the Bs for the Fe3Si and Fe-B phases. The calculated Bs of Fe3Si is 1.35 T, and that of Fe-B varies from 2.08 to 2.22 T based on Fe to B ratios. Therefore, a total Bs higher than 1.80 T can be obtained with y ≥ 4 for both x = 1 and 2 in Fe90−xCuxSi10−yBy.