Abstract
Current induced spin-orbit torques driven by the conventional spin Hall effect are widely used to manipulate the magnetization. This approach, however, is nondeterministic and inefficient ...for the switching of magnets with perpendicular magnetic anisotropy that are demanded by the high-density magnetic storage and memory devices. Here, we demonstrate that this limitation can be overcome by exploiting a magnetic spin Hall effect in noncollinear antiferromagnets, such as Mn
3
Sn. The magnetic group symmetry of Mn
3
Sn allows generation of the out-of-plane spin current carrying spin polarization collinear to its direction induced by an in-plane charge current. This spin current drives an out-of-plane anti-damping torque providing the deterministic switching of the perpendicular magnetization of an adjacent Ni/Co multilayer. Due to being odd with respect to time reversal symmetry, the observed magnetic spin Hall effect and the resulting spin-orbit torque can be reversed with reversal of the antiferromagnetic order. Contrary to the conventional spin-orbit torque devices, the demonstrated magnetization switching does not need an external magnetic field and requires much lower current density which is useful for low-power spintronics.
Spinel Zn1‐xCuxGa2O4 (x = 0‐0.15) ceramics were prepared by the conventional solid‐state method. Only a single phase was indexed in all samples. The continuous lattice contraction of ZnGa2O4 unit ...cell was caused by Cu2+ substitution, and the lattice parameter shows a linear correlation with the content of Cu. The refined crystal structure parameters suggest that Cu2+ preferentially occupies the octahedron site, and the degree of inversion of Zn1‐xCuxGa2O4 (x = 0‐0.15) ceramics almost equals to the content of Cu2+. The relative intensity of A*1g mode in Raman spectra confirm that the degree of inversion climbed with the growing content of Cu2+. The experimental and theoretical dielectric constant of Zn1‐xCuxGa2O4 ceramics fit well. Zn1‐xCuxGa2O4 (x = 0.01) ceramics sintered at 1400°C for 2 h exhibited good microwave dielectric properties, with εr = 9.88, Q × f = 131,445 GHz, tanδ = 6.85 × 10−5, and τf = −60 ppm/°C.
BaTiO
3
powders was synthesized from cheap and readily available H
2
TiO
3
and Ba(OH)
2
by solid-state reaction at low temperature. The samples were characterized by thermogravimetry and differential ...scanning calorimetry (TG-DSC), X-ray diffraction (XRD), Scanning electron microscope (SEM), Raman spectroscopy, Fourier-Transform Infrared Spectroscopy (FTIR). The results show that the pure cubic BaTiO
3
powders with an average size of about 68 nm was prepared at 600℃ for 4 h and Monodisperse tetragonal (c/a = 1.0100) BaTiO
3
powder with an average size of about 242 nm was prepared by calcination at 900℃ for 4 h, suggesting its promising applications in multilayer ceramic capacitors (MLCC). Compared with BaCO
3
and TiO
2
as raw materials, Due to the low decomposition temperature of Ba(OH)
2
and the small particle size of H
2
TiO
3
, the synthesis temperature of pure BaTiO
3
decreased by 200℃, and the phase transition temperature decreased by 100℃. The method can be used to synthesize functional ceramic powders with different crystal phase levels.
Four BT-based ceramic samples were prepared using a grain grading approach. The bigger-grained (∼100 nm) and smaller-grained (∼70 nm) BaTiO3 (BT) powders were mixed. The smaller-grained BT powder ...controlled the average grain size and guaranteed the reliability, while the bigger-grained powder enhanced the dielectric constant. Various percentages of bigger-grained BT powder were introduced to balance the average grain size and the dielectric constant. As the proportion of bigger grains increased, the dielectric constant (εr) improved significantly. The room-temperature εr of 25% bigger-grain mixed BT (2623) was ∼50% higher than that of the sample with a similar average grain size without grain grading. The ceramic mixed with 15% bigger-grained BT showed comprehensive dielectric performance, which met the EIA X5R standard and provided a considerable εr of 1841 along with a low dielectric loss of 0.78%. Notably, the average grain size was 90 nm, which favors the applications in ultra-thin multilayer ceramic capacitors.
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Rare earth (RE)-doped BaTiO
3
materials are promising dielectric materials for base-metal electrode multilayer ceramic capacitors (BME-MLCCs). Thus, the fundamental understanding of their effect on ...dielectric properties and reliability is crucial for further improvement of its performance. Herein, according to Preisach model, the dielectric stability of Dy and Y-doped BaTiO
3
MLCCs with different particle sizes was investigated in this study. First order reversal curve (FORC) analysis showed that the reversible and irreversible domain wall motion of Dy-doped samples was weaker than that of Y-doped samples. Results also showed that the higher “shell” proportion of “core-shell” structure in Dy-doping was beneficial for improving the dielectric stability and insulation resistance degradation. The findings provide a comprehensive understanding and illustrate the significant role of the “core-shell” volume ratio in the tetragonality and domain wall motion in RE-doped BaTiO
3
materials, and consequently laying an important ground work to obtain high dielectric stability and reliability in BME-MLCCs.
Abstract
This work investigates the synthesis, chemical composition, defect structures and associated dielectric properties of (Mg
2+
, Ta
5+
) co-doped rutile TiO
2
polycrystalline ceramics with ...nominal compositions of (Mg
2+
1/3
Ta
5+
2/3
)
x
Ti
1−
x
O
2
. Colossal permittivity (>7000) with a low dielectric loss (e.g. 0.002 at 1 kHz) across a broad frequency/temperature range can be achieved at
x
= 0.5% after careful optimization of process conditions. Both experimental and theoretical evidence indicates such a colossal permittivity and low dielectric loss intrinsically originate from the intragrain polarization that links to the electron-pinned
$${\bf{M}}{{\bf{g}}}_{{\bf{T}}{\bf{i}}}^{{\prime}{\prime} }+{{\bf{V}}}_{{\bf{O}}}^{\bullet \bullet }+{\bf{2}}{\bf{T}}{{\bf{a}}}_{{\bf{T}}{\bf{i}}}^{\bullet }+{\bf{2}}{\bf{T}}{{\bf{i}}}_{{\bf{T}}{\bf{i}}}^{\prime}$$
M
g
T
i
′
′
+
V
O
•
•
+
2
T
a
T
i
•
+
2
T
i
T
i
′
defect clusters with a specific configuration, different from the defect cluster form previously reported in tri-/pent-valent ion co-doped rutile TiO
2
. This work extends the research on colossal permittivity and defect formation to bi-/penta-valent ion co-doped rutile TiO
2
and elucidates a likely defect cluster model for this system. We therefore believe these results will benefit further development of colossal permittivity materials and advance the understanding of defect chemistry in solids.
Realizing a high color rendering index (CRI) in Ce:LuAG transparent ceramics (TCs) with desired thermal stability is essential to their applications in white LEDs/LDs as color converters. In this ...study, based on the scheme of configuring the red component by Cr
3+
doping, an efficient spectral regulation was realized in Ce,Cr:LuAG TCs. A unilateral shift phenomenon could be observed in both photoluminescence (PL) and photoluminescence excitation (PLE) spectra of TCs. By constructing TC-based white LED/LD devices in a remote excitation mode, luminescence properties of Ce,Cr:LuAG TCs were systematically investigated. The CRI values of Ce:LuAG TC based white LEDs could be increased by a magnitude of 46.2%. Particularly, by combining the as fabricated Ce,Cr:LuAG TCs with a 0.5 at% Ce:YAG TC, surprising CRI values of 88 and 85.5 were obtained in TC based white LEDs and LDs, respectively. Therefore, Ce,Cr:LuAG TC is a highly promising color convertor for high-power white LEDs/LDs applied in general lighting and displaying.
Ultrafine ceramic powders with high tetragonality are the fundamental for the multi-layer ceramic capacitors (MLCCs). In this study, an efficient method of atmospherically hydrothermal assisted ...solid-state synthesis for ultrafine BaTiO
3
particles is presented. The BaTiO
3
nanopowders with homogeneous distribution, a mean particle size ~ 260 nm and high tetragonality of 1.0095 were obtained by at the optimal parameters of hydrothermal time of 6 h, Ba(OH)
2
·8H
2
O/BaCO
3
= 0.25/0.75 and calcination temperature of 1000
o
C. XRD and HRTEM analyses revealed a “core-shell” structure of TiO
2
@BaTiO
3
formed in the first-step hydrothermal process, which reduces the diffusion distance between BaCO
3
and TiO
2
, resulting in a lower calcination temperature at the second-step solid-state reaction. Compared with pure hydrothermal and solid-state reaction processes, the atmospherically hydrothermal assisted solid-state synthesis in this study shows larger ability for improving the particle size distribution and the tetragonality, reducing defects of BaTiO
3
particles. In particular, the grain size, sintering density, and dielectric constant at the Curie temperature of BaTiO
3
ceramics are 1.93 μm, 98%, and 7066, respectively. In the solid-state reaction stage, the lattice diffusion distance from BaO to TiO
2
tends to decrease due to the formation of BaTiO
3
shells, thus, high tetragonal and relatively small particle size of BaTiO
3
powder was synthesized. This work presents a method for preparing ultrafine BaTiO
3
powders with large tetragonality for MLCCs.
Tetragonal-phase BaTiO
3
powders of particle size 370 nm were synthesized by microwave sintering at 850 °C. The raw materials were BaCO
3
, TiO
2
, and alanine. SiC microspheres were used as ...microwave conductors. The effects of the holding time, sintering aids, and SiC addition on the preparation of BaTiO
3
were investigated. The results indicate that the addition of SiC as a microwave acceptor leads to formation of microwave micro-regions. This enables uniform heating of the raw materials and decreases the calcination temperature needed to obtain BaTiO
3
. Alanine coordinates with Ba, and this loosens the metal–CO
3
bond and promotes separation of CO
2
, decreases the BaCO
3
decomposition temperature, and provides a higher nucleation site density. It gives an idea about the microwave solid-state synthesis of BaTiO
3
powder.
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