Indications of c-axis Charge Transport in Hole Doped Triangular Antiferromagnets

The c-axis charge transport of the hole doped triangular antiferromagnet is investigated within the t-J model by considering the incoherent interlayer hopping. It is shown that the c-axis charge transport of the hole doped triangular antiferromagnet is essentially determined by the scattering from the in-plane fluctuation. The c-axis conductivity spectrum shows a low-energy peak and the unusual high-energy broad band, while the c-axis resistivity is characterized by a crossover from the high temperature metallic-like behavior to the low temperature insulating-like behavior, which is qualitatively consistent with those of the hole doped square lattice antiferromagnet.

High temperature thermoelectric properties of highly c-axis oriented Bi_2Sr_2Co_2O_y thin films fabricated by pulsed laser deposition

High-temperature thermoelectric transport property measurements have been performed on the highly c-axis oriented Bi2Sr2Co20v thin films prepared by pulsed laser deposition on LaA1Oa （001）. Both the electric resistivity p and the seebeck coefficient S of the film exhibit an increasing trend with the temperature from 300 K-1000 K and reach up to 4.8 m. cm and 202 V/K at 980 K, resulting in a power factor of 0.85 mW/mK which are comparable to those of the single crystalline samples. A small polaron hopping conduction can be responsible for the conduction mechanism of the film at high temperature. The results demonstrate that the Bi2Sr2Co2Oy thin film has potential application has high temperature thin film thermoelectric devices,

Atomistic simulation of the structural evolution in magnesium single crystal under c-axis tension

Molecalar dynamics simulation is applied to investigate the microstructure evolution of magnesium single crystals under c-axis extension at different temperatures. At low temperatures, both {1012} and {1011} twins are observed. At elevated temperatures, {1011} twining decreases quickly with increasing temperature, while the amount of {1012} twins increases. The （1012} twin is found to be the main deformation mechanism under the c-axis tension in the magnesium single crystal. Meanwhile, shear bands are also observed during deformation. When the temperature is beyond 500 K, the non-basal plane slip due to the thermal .activation is found. The stress-strain curves related with deformation behavior at atomistic scale are presented.

Substrate angle-induced fully c-axis orientation of AlN films deposited by off-normal DC sputtering method

A highly c-axis-oriented aluminum nitride(Al N)thin film with smooth and crack-free surface was fabricated by an off-normal direct current(DC)sputtering method in a pure nitrogen atmosphere,in which the rotatable substrate holder positioned in the middle of four side targets was a key approach to guarantee the grain growth with no tilt.The detailed effects of substrate angle on the c-axis orientation of Al N films were investigated by varying the substrate angle from 0°to 90°.Moreover,theoretical analysis and Monte Carlo(MC)simulation reveal that the oblique or even vertical angle could improve the lateral kinetic energy of sputtered atoms deposited on the growing film.A variety of examining techniques including X-ray diffraction(XRD),(002)peak rocking curve,scanning electron microscopy(SEM)were conducted to evaluate the angle dependence on the crystallographic orientation.These test results indicate that larger substrate angle is beneficial to the(002)growth of Al N thin film,and a fully c-axis textured Al N thin film is obtained at 90°with small surface roughness(R_(a))of 3.32 nm.

Deformation Structures of the Madao Gneiss in South Qinling:Structural Analysis,Geochronological Constraints,and Tectonic Implications

The tectonic evolution of South Qinling, which is a main part of the Qinling orogenic belt, is still in dispute and deformation history of South Qinling is poorly studied. In this paper, detailed structural, microstructural, quartz c-axis fabric analysis, and geochronology results for the Madao gneiss in South Qinling are presented to characterize the deformation history. Results show that rocks in the northern part （Tiefodian-Laozhanggou） experience general shearing and deform at relative low temperature. The shear sense generally is south to north. In contrast, rocks in the southern part （Laozhanggou-Panjiahe） are weakly sheared with pure shear features and evidence of high- temperature deformation. Based on the analyses, we conclude that there exist two distinct deformation geometries in the Madao gneiss and accordingly we can divide the deformation into two stages. The early stage is represented by regional shortening, while the late stage features northward thrust shearing and evidence shows that it was a progressive process between them. LA-ICP MS U-Pb dating of zircons from pre-deformational migmatite veins yields age of 198.5 ±2.0 Ma. This result, in combination with the age of post-deformational granite, indicates that the northward thrust shearing of the Madao gneiss occurred in the Late Triassic. In view of these results and other reported data in South Qinling, we propose that deformation in Madao gneiss may result from the initial collision and subsequent northward accretion in Late Triassic.

Magnetic texture of Nd_(2)Fe_(14)B solidified in the surface layer of anisotropic sintered-magnets

The arrangements of the easy magnetization axis[001]of columnar Nd_(2)Fe_(14)B crystals in the laser scanned layer on anisotropic sintered Nd_(15)Fe_(77)B_(8)magnets were investigated by XRD and the Bitter method.The results show that the common effects of both the heat flux and the substrate magnetization orientation constrain the columnar Nd_(2)Fe_(14)B solidified from the laser melting pool to form the c-axis texture orientated with the same direction as that of the substrate,when the geometric relationship between the heat flux in the laser scanning layer and c-axis texture orientation of the substrate is perpendicular to each other,and if the laser scanning velocity is no less than 25 mm·min^(-1).The c-axes of columnar Nd_(2)Fe_(14)B crystals are no longer randomly distributed in the plane normal to their preferential growing direction as they are randomly done in both ingots cooled by water-cooling copper mould and directionally solidified Nd-Fe-B rods.

The c—Axis Infrared Conductivity of a dx^2—y^2— Wave Superconductor with the Hopping Assisted by the Spin Fluctuations

A theory of the c-axis infrared conductivity of a dx2-y2-wave superconductor due to the competition between the interlayer direct hopping and the hopping assisted by the spin fluctuations has been developed. The prediction of our theory captures the main feature of the experiment. Thus we argue that the anomalous behavior of the c-axis infrared conductivity of the underdoped cuprates in superconducting state may be properly understood within the theory.

REPEATED COMPRESSION-ANNEALING EXPERIMENTS ON ANISOTROPIC CORE ICE

Three runs (6 samples) of repeated uniaxial compressionannealing experiments were conducted on a creep testing machine with a loading accuracy of 1 % at-2±0.2℃. The tested samples were cut from BHQ ice core. Compression axes were parallel, at an angle of 45°and normal to the vertical of the core respectively. The initial orientation fabrics of samples were single-maximum pattern or approximate single-maximum pattern with different mean grain size. The sample was compressed with an initial axial stress of 0.8 MPa, until 10% axial strain was obtained, and then annealed for 72 hours. Such compression-annealing procedure was lepeated 6 times for a run.The experimental result shows that under a warm temperature and large load, the initial features of structure and fabric disappear finally, and n small circle girdle fabric with fine equigranular grains appears, and a multi maxima fabric developes to seme extent. Analysis of structure and fabric shows that the formation mechanism of new fabrics in these experiments is principally recrystallization. With the repetition of compression-annealing, the difference in the fabric of the six samples is reducing, their rheological behavior tends to be uniform, and their grain size decreases towards a steaty state value.

Transformation from Neoproterozoic Sinistral to Early Paleozoic Dextral Shearing for the Jingdezhen Ductile Shear Zone in the Jiangnan Orogen, South China

The Jingdezhen ductile shear zone is evolved from the Neoproterozoic Zhangyuan ophiolite melange belt in the eastern Jiangnan Orogen, South China. Comprehensive study of geometry, kinematics, quartz c-axis fabric, temperature-pressure conditions and geochronology were conducted in this study. The Jingdezhen shear zone extends -180 km along the NE orientation with two groups of subvertical fo- liation and subhorizontal lineation. One group of foliation strikes NEN orientation whereas another one NEE orientation. Field investigation, microscopic observation and quartz c-axis fabric show that sinistral shearing along NEN-striking foliation occurred earlier than dextral shearing along NEE-striking foliation. Syn-tectonic staurolite porphyroblasts and deformation manner of feldspar imply that sinistral shearing occurred at 530-420 ℃ and 6-2 kbar. Deformation manner and c-axis fabric of quartz and pre-tectonic staurolite porphyroblasts indicate that dextral shearing took place at 420-300 ℃. LA-ICP-MS zircon U-Pb and mica ^40Ar/^39Ar dating indicate that the sinistral shearing occurred during Neoproterozoic oro- geny （830-800 Ma） whereas the dextral shearing at 447＋12 Ma. The sinistral shearing resulted from the Neoproterozoic final assembly between the Yangtze and Cathaysia blocks. The dextral shearing was caused by Early Paleozoic orogen parallel extension and clockwise rotation.

Emplacement and deformation of Shigujian syntectonic granite in central part of the Dabie orogen:Implications for tectonic regime transformation

The Shigujian pluton is a gneissic quartz monzonite located in Tiantangzhai area in central part of the Dabie orogen.Anisotropy of magnetic susceptibility(AMS) data show that most magnetic foliations dip steeply to southeast.About 85% of sampling points dip from 40° to 90°.Magnetic foliations are generally parallel to the foliations measured in the field.The pluton has NWW-SEE trending lineations in the southeast and NE-SW trending lineations in central part and north,but the lineations plunge to SW in central part and to NE in the north.All plunges are moderate.The anisotropy degree(P) is between 1.065 and 1.532 and the shape parameter(T) is between 0.005 and 0.694.A Flinn diagram of the magnetic fabrics shows that the value of K is less than 1.The analysis of AMS suggests that the pluton was emplaced and deformed under a SE-NW compressional stress regime.The analysis of quartz C-axis fabrics indicates that the pluton was deformed under compressional stress and deformation temperatures range from 400 to 500℃.Microstructures indicate that the pluton is deformed in near solidus conditions and the pluton is a synkinematic intrusion.The emplacement of the Shigujian granite is inferred to have taken place syntectonically.The zircon U-Pb dating of the granite suggests that the pluton was intruded at 141±2.3 Ma.By synthesizing all data,it seems that the Shigujian pluton was emplaced in a compressional environment and the transformation time of the Dabie orogen from compression to extension took place after 141 Ma.The structural evolution of the Dabie orogen was controlled by the Pacific tectonic domain when the Shigujian pluton was emplaced,whereas the adjacent Tiantangzhai complex massif is the result of an extensional environment.

Microstructure evolution of hot-deformed SmCo-based nanocomposites induced by thermo-mechanical processing

Nanocomposite permanent magnets have ultra-high theoretical magnetic energy products,due to cou-pling of the soft/hard magnetic phases,inciting strict microstructural requirements.In this study,the microstructure evolution,including the phase transition,morphological changes,and texture formation,of hot-deformed SmCo-based nanocomposites under thermal-stress-strain coupling was characterized to determine a possible strategy for achieving high performance.The SmCo_(5)/α-Fe nanocomposites precursor contained fine and dispersed Sm(Fe,Co)_(5)and Fe-Co grains and exhibited a two-stage phase transforma-tion accompanied by grain growth.In the early stage of deformation at relatively low temperature,the adjacent Sm(Co,Fe)5 and Fe-Co phase formed the Sm_(2)(Co,Fe)_(17)-H phase,which was stable only with small grain sizes.In the high-temperature deformation stage,the Sm_(2)(Co,Fe)_(17)-H phase transformed into the Sm_(2)(Co,Fe)_(17)-R phase with large grain sizes.In addition,the strong c-axis texture formed in the Sm(Co,Fe)_(5)phase but not in the Sm_(2)(Co,Fe)_(17)-R phase.Subsequently,the phase transition process and texture formation mechanism were systematically analyzed by transmission electron microscopy.The ini-tiation of a slip system and/or preferential grain growth explained the formation of texture under the action of uniform stress and strain and assisted by dispersed Sm-rich nanograins.The Sm_(2)(Co,Fe)_(17)-R grains with poor orientations and large grain sizes did not achieve magnetic hardening,which also dam-age the magnetic properties.According to the results of this work,we also presented a new strategy to prepare high-performance SmCo-based nanocomposites magnets.

Microstructure and magnetic fabric in the Shuanghe pluton:A synkinematic granite in Eastern Dabie Mountains,China

Strain analyses for the Shuanghe pluton show that the main strain planes suffered distinct deformation. The main strain value (XZ) is up to 1.59–2.18, and the value of Flinn index (K) ranges from 0.11 to 0.82. Anisotropy of magnetic susceptibility (AMS) measurements reveal that the orientations of the magnetic foliation and lineation gently dip SE, consistent with the macroscopic foliation of the pluton. The value of anisotropy degree (P) ranges from 1.109 to 1.639, and the shape parameter (T) from 0.079 to 0.534. These studies prove that the pluton was deformed under strong compression. Quartz c-axis textures, defined by monoclinic or triclinic asymmetry, usually developed the high maxima paralleling the b-axis, which is defined by the prismatic slip (1010) under the high temperature. These fabrics are quite different from those developed in the high-ultrahigh pressure rocks (UHP) which were captured in the pluton or country rocks. It is concluded that the Shuanghe pluton emplaced under regional compression slightly after the formation of UHP, and it is characterized by synkinematic granitic deformation.

Analysis on deformation and texture formation mechanism of hot-deformed Nd-Fe-B magnets based on heterogeneous structure evolution

In this paper, microstructure, micromagnetic structure, texture, together with magnetic properties of the hot-deformed(HD) Nd-Fe-B magnets were systematically studied to understand the deformation process and the formation mechanism of c-axis texture. The results show that the platelet grains are formed in the fine-grain regions at the initial stage of the deformation. As the amount of deformation increases, the proportion of platelet grains increases and arranges gradually, causing the formation of c-axis texture, till the grain merging occurres when the deformation is excessive. It should be noted that the rare earth-rich phase in the fine-grained region slowly diffuses to the coarse-grained region where only grain growth can be observed during deformation. The deformation mechanism and formation of c-axis texture in HD Nd-Fe-B magnets can be deduced to be accomplished by the processes of dissolution-precipitation diffusion, grain rotation and grain arrangement, based on the characterization of microstructure and texture evolution. Also, approaches to optimize the preparation process and magnetic properties of the hot-deformed Nd-Fe-B magnets were discussed.

Atomistic simulation of tension deformation behavior in magnesium single crystal

The deformation behavior in magnesium single crystal under c-axis tension is investigated in a temperature range between 250 K and 570 K by molecular dynamics simulations. At a low temperature, twinning and shear bands are found to be the main deformation mechanisms. In particular, the {102} tension twins with the reorientation angle of about 90 °are observed in the simulations. The mechanisms of {102} twinning are illustrated by the simulated motion of atoms. Moreover, grain nucleation and growth are found to be accompanied with the {102} twinning. At temperatures above 450 K, the twin frequency decreases with increasing temperature. The {102} extension twin almost disappears at the temperature of 570 K. The non-basal slip plays an important role on the tensile deformation in magnesium single crystal at high temperatures.