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In this paper, a high-dense alumina ceramics were prepared through the two-step pressureless sintering process with high-purity alumina powder as raw materials and high-purity MgO as sintering aids. The effects of the sintering temperature in the first-step (T1) and the soaking time (t) in the second sintering step (T2) on the density, microstructure and mechanical properties of the alumina ceramics were studied. The results indicated that the relative density increased with the increase of T1 temperature whereas it increased and then decreased with the increase of MgO content. Higher T1 temperature and extended soaking time caused larger grain size, which accompanied with the Ostwald ripening of the grain and led to non-uniformity of grain size distribution. The addition of MgO was beneficial to the decrease in grain size due to pinning effect of the second phase. For samples with shorter soaking time, sintering with higher T1 temperature led to better mechanical properties because of its high density. However, for the long soaking time, all samples after sintering at different T1 temperature were fully-densified, so the grain size become to the dominant factor of strength, thus samples with lower T1 temperature exhibited better mechanical properties due to the refinement grain. Excessive addition of MgO resulted in defects, by which the strength increased firstly and then decreased slightly with the increased MgO content. For the samples with 2.5wt.% MgO, the optimum condition for the two-step pressureless sintering was T1=1450°C and T2=1400°C for 20h, and the obtained sample achieved the relative density of 96% and the strength of 507±32MPa.

In this paper, clay bonded silicon carbide was prepared through pressureless sintering process with silicon carbide dusting powder as raw materials and clay as sintering additive. The effects of the ball-milling method, sintering temperature and clay contents on the density, microstructure and mechanical properties of clay bonded silicon carbide refractory were studied. The planetary ball-milling was a good method to improve the density of the green body, and the density was increased simultaneously with an increase of the clay content. The liquid phase derived from low-melting eutectic mixtures of clay could prevent the superlative oxidation of silicon carbide. The mass increment of sintered samples decreased firstly and then increased at the sintering temperature range from 1250 to 1500 °C. The open porosity of samples decreased with the clay addition at a content range from 10 to 30 wt.%. The bending strength of the samples decreased firstly and then increased with the clay addition increasing. The optimum condition for preparing clay bonded silicon carbide with silicon carbide dusting powder was sintering at 1350 °C with 20 wt.% clay, and the obtained sample with a porosity of 24% achieved the bending strength of 78±7 MPa.

Transparent polycrystalline alumina with high bending strength has been fabricated using two-step pressureless sintering. The microstructure and mechanical property has been investigated by varying the MgO doping concentration and sintering parameters. The results showed that the grain size markedly decreased with the increasing content of MgO addition. Although the density of alumina could be increased by the higher temperature for the first sintering step, the larger grain would depress the bending strength. Hence, the optimum bending strength was achieved with 0.5 wt% MgO with the two-step sintering of 1450°C for 20 min and 1400°C for 20 h. The Vickers hardness of the transparent PCA increased doping content, and the variation tendency was well accelerated with the relative density, indicated that the porosity plays a more important on hardness than the grain size.

In this paper, reaction bonded silicon carbide (RBSC) was prepared by silicon infiltration with silicon carbide and carbon black as raw materials. The effects of the mixing methods with different binders on density of green body were compared. The influences of phenolic resin content, forming pressure, sintering temperature of samples on the performance of green body, mechanical microstructure and properties of RBSC were studied. The result shows that the density of green body by wet-mixing with alcohol-soluble binder (phenolic resin) was much better than semi-dry-mixing with usual water-soluble binders (polyvinyl alcohol and carboxy methyl cellulose sodium). The bending strength of green body prepared with phenolic resin at the content of 12 wt.% reached to the maximum value. The density of RBSC increased generally with phenolic resin content increasing at temperature range from 1550 to 1650 °C. The bending strength of RBSC increased firstly and then decreased with phenolic resin content increasing at a sintering temperature of 1600 °C. The optimum condition for fabricating RBSC was sintering at 1600 °C with 12 wt.% phenolic resin, the density, porosity and bending strength of the obtained RBSC was 3.06 g·cm-3, 0.05% and 370±54 MPa, respectively.

We reported microwave measurements on a nanoscale MgO-based magnetic tunnel junction having an elliptical shape with large aspect ratios to obtain enough in-plane shape anisotropy to ensure free layer magnetization along the long axis. Combined with the magnetization of a synthetic antiferromagnet pinned layer along the short axis, this results in the perpendicular configuration between the magnetizations of free and pinned layers. A steady high frequency oscillation up to 5 GHz was achieved in such devices at zero magnetic field. Meanwhile, a large frequency tunability of 0.11 Hz·cm2/mA (2.67 GHz/mA) was obtained. The micromagnetic simulations confirm the origin of the high oscillation frequency of our spin transfer nano-oscillators (STNOs). These results suggest the great possibility of improved integration and potential application of STNOs for developing the next-generation of on-chip oscillators.

We report electric field control of the interfacial Dzyaloshinskii-Moriya interaction (DMI) in MgO/Fe/Pt multilayers. The interfacial DMI is obtained and quantified by Brillouin light scattering measurements based on the frequency nonreciprocity of spin waves in a ferromagnet. The magnitude of the induced DMI is found to linearly increase as a function of electric field intensity. The efficiency of electric field control of the interfacial DMI characterized as a ratio of the DMI energy change to the electric field, which is found to be equal to 67 fJ/(Vm) with a positive electric field. We further demonstrate that the origin of the enhanced DMI results from the MgO/Fe interface. The Rashba spin-orbit coupling and electric field induced anisotropy at the MgO/Fe interface might be responsible for the enhanced interfacial DMI. Our findings open up a way for exploring the spintronic devices with a tunable DMI.

An oscillatory variation of saturation magnetization ( M s ) with the thickness of Cr layers has been found in Fe-Si/Cr multilayered films prepared by rf sputtering under 5 mTorr Ar charging pressure. A conversion electron Mossbauer spectroscopy (CEMS) study showed that the oscillatory variation of M s does not result from antiferromagnetic coupling effect, but mainly from an oscillatory change in the paramagnetic component of the Fe-Si layers. This oscillatory change in the paramagnetic component in the Fe-Si layers is due the unusual interlayer coupling effect through the Cr layers.

Fe-Si/Cr multilayer films with Cr layers of various thicknesses have been obtained by rf sputtering at low Ar charging pressure of 5 mTorr. On increasing the thickness of the Cr layers an oscillatory variation of magnetization with a period of about 10 A is found. This is caused by the oscillatory change in the thickness of the dead layer.

The polar Kerr rotation and ellipticity spectra of the as-deposited and annealed Zn1−xCoxO inhomogeneous magnetic semiconductors were measured. The Kerr rotation spectra versus the photon energy can be greatly modulated by adjusting the Co concentration or annealing the samples. Moreover, the observed maximal Kerr rotation, 0.72°, in an annealed sample is higher than that of pure Co films, Pt∕Co multilayers, and PtxCo1−x alloys. The enhanced Kerr rotation in the annealed samples can be explained by the fact that the annealed samples became a nanocomposite system consisting of Co clusters and Zn1−xCoxO magnetic semiconductor.

CoNb/Cu multilayers with amorphous CoNb magnetic layers were prepared by rf-sputtering method and then annealed at various temperatures in a high vacuum. A maximum magnetoresistance ratio of 2.83% at room temperature was obtained under a relatively low saturation field of about 200 Oe for the optimum annealing temperature of 400° C. The structural, magnetic and transport properties were strongly influenced by the annealing temperature, and the transport properties were explained on the basis of granular multilayered structures. The magnetoresistance ratio also depends on the thickness of CoNb and Cu layers.