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First-principles calculations were performed to calculate the electronic structures of low temperature phase (LTP) MnBi (Mn50Bi50) and substitutionally and interstitially Sn-doped MnBi [Mn50Bi25Sn25, (Mn0.5Bi0.5)66.7Sn33.3]. Brillouin function predicts the temperature dependence of saturation magnetization M(T). Sn substitution for Bi in MnBi (Mn50Bi25Sn25) changes the magnetocrystalline anisotropy constant (Ku) from −0.202 MJ/m3 (the in-plane magnetization) for LTP MnBi to 1.711 MJ/m3 (the out-of-plane magnetization). In comparison, the Ku remains negative but slightly decreases to −0.043 MJ/m3 when Sn is interstitially doped in MnBi [(Mn0.5Bi0.5)66.7Sn33.3]. The Curie temperature (TC) decreases from 716 K for LTP Mn50Bi50 to 445 K for Mn50Bi25Sn25 and 285 K for (Mn0.5Bi0.5)66.7Sn33.3. Mn50Bi25Sn25 has a lower magnetic moment of 5.034 μB/f.u. but a higher saturation magnetization of 64.2 emu/g than (Mn0.5Bi0.5)66.7Sn33.3 with a magnetic moment of 6.609 μB/f.u. and a saturation magnetization of 48.2 emu/g because the weight and volume of the substitutionally Sn-doped MnBi are smaller than the interstitially Sn-doped MnBi. The low Curie temperature and magnetization for Sn-doped MnBi are attributed to the high concentration of Sn. Thus, future study needs to focus on low Sn-concentrated MnBi. [ABSTRACT FROM AUTHOR]

Today's circuit technology requires low-power transistors and diodes to extend Moore's law. While research has been focused on reducing power consumption of transistors, low-power diodes have not been widely studied. Here, we report a low-power, thus steep-slope Schottky diode, with a "cold metal" source. The Schottky barrier between metal electrode and bulk MoS2 enabled the diode behavior, and the steep-slope diode IV curve originated from the change in the density of states of a graphite (cold metal) source with a bias voltage. The MoS2 Schottky diode with a cold metal exhibits an ideality factor (η) < 1 for more than four decades of drain current with a sizable rectifying ratio (108). The realization of a steep-slope Schottky diode paves the way to the improvement in low-power circuit technology. [ABSTRACT FROM AUTHOR]

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 600-650K. 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 300K, thereby satisfying desired magnetic properties for heat-assisted magnetic recording media to achieve 4 Tb/in.2 areal density. [ABSTRACT FROM AUTHOR]

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 ε→τ in the B-N-doped ε-MnAl occurs at the temperatures above 680 K and accomplishes at 760 K, both of which are slightly higher than those of the ε-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. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

Ferroelectric Pb[sub 0.99][(Zr[sub 0.6]Sn[sub 0.4])[sub 0.85]Ti[sub 0.15]][sub 0.98]Nb[sub 0.02]O[sub 3] (PZSTN) thin films with different preferred orientations were fabricated by modifying with 20 mol% excess lead that contained a Pb(Zr[sub x]Ti[sub x-1])O[sub 3] seed layer (x = 0,0.3,0.52,0.65). Ferroelectric properties were investigated in terms of the texturing character of the PZSTN thin film. With an increase in Zr content in the seed layer, the (100) texturing of the PZSTN film was enhanced. The highly (100) texture (∼97%) was developed by inserting a seed layer with x = 1 between the Pt-coated substrate and the PZSTN thin film, whereas in the case of annealing in a reduced condition, the orientation of the film became nearly (111). The (111)-oriented PZSTN film showed relatively higher remanent polarization compared to that of the (100)-oriented film, while the (100)-oriented PZSTN film showed more fatigue behavior than the (111)-oriented film after 10[sup 9] switching cycles. The (111)-oriented PZSTN film with rhombohedral structure is believed to be suspected to significant stress along applied field direction, resulting in the production of many defects, causing degradation of the polarization during switching cycles. [ABSTRACT FROM AUTHOR]

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 electrode edge. As a result, with increasing ferroelectric thickness, the emission charge increased and the threshold field decreased. However, there was no apparent difference between the emission charges from the different upper electrode diameters. © 2002 American Institute of Physics. [ABSTRACT FROM AUTHOR]

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 degreesC. 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 C/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. c 2001 American Institute of Physics. [DOI: 10.1063/1.1388572]
the main purpose of this investigation is to study the dielectric and piezoelectric properties of PMN-PZT thin films with various compositions and to develop a high-performance composition of the PMN-PZT thin film suitable for actuator applications. [ABSTRACT FROM AUTHOR]

Little is known about the physical properties of Mn4C for which is unstable and difficult to prepare. We herein report on the unusual thermomagnetic properties of high purity Mn4C powders obtained by plasma melting and magnetic separation processes. The saturation magnetization of Mn4C increases linearly with increasing temperature in the range of 50 K–590 K and remains stable at temperatures below 50 K. The anomalous magnetization increases of Mn4C with increasing temperature can be considered in terms of the Néel's P-type ferrimagnetism. At temperatures above 590 K, the Mn4C decomposes into Mn23C6 and Mn, which would be partially oxidized into manganosite when exposed to air. The remanent magnetization of Mn4C varies little with temperature. The Curie temperature of Mn4C is around ∼870 K. The positive temperature coefficient (∼0.0072 Am2 kg−1 K−1) of magnetization in Mn4C makes it potentially important in controlling the thermodynamics of magnetization in magnetic materials. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

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 applicable to very high frequency: 30-300 MHz) and ultra high frequency: 300 MHz-3 GHz) devices. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

A correction is presented to the article "Enhancing the magnetization of Mn4C by heating" which appeared in the May 10, 2018 issue.

0.2Pb(Mg[sub 1/3]Nb[sub 2/3])O[sub 3]–0.8Pb(Zr[sub 0.5]Ti[sub 0.5])O[sub 3] (0.2PMN–0.8PZT) thin films were deposited on Pt(111)/Ti/SiO[sub 2]/Si [Pt(111)] and Pt(200)/SiO[sub 2]/Si [Pt(200)] substrates by a sol–gel method, and the effect of orientation on the piezoelectric and dielectric properties of 0.2PMN–0.8PZT thin films was investigated. The 0.2PMN–0.8PZT thin films on Pt(111) and Pt(200) showed strong (111) and (100) preferred orientations, respectively. The spontaneous polarization of the (111) oriented film was higher than that of the (100) oriented film. However, the (100) oriented film showed a higher dielectric constant (K) and transverse piezoelectric coefficients (d[sub 31]) than the (111) oriented film. Because the spontaneous polarization direction of the (100) oriented film is more tilted away from the normal to the film surface than that of the (111) oriented film, the dielectric constant and the transverse piezoelectric coefficient (d[sub 31]) of the (100) oriented film were enhanced. © 2001 American Institute of Physics. [ABSTRACT FROM AUTHOR]