Effect of composition on texture and magnetic the crystallographic properties of the Sm（Co,Fe,Cu,Zr）z ribbons prepared by simple processing

Sm（CObalFeyCuxZrw）z ribbons have been prepared by melt spinning at a low wheel velocity followed by shorttime aging and slow cooling the as-spun ribbons from 850 to 400℃. It is found that the composition can significantly influence the degree of crystallographic texture of the ribbons. The 1：7 phase of the as-spun ribbons is segregated into 1：5 and 2：17 phases by the simple processing procedure ribbons after precipitation hardening. （BH）max about by the adjustment of composition. However, the crystallographic texture is still preserved in the 86kJ/m^3 can be obtained in the Sm（Co, Fe, Cu, Zr）z ribbons

Magnetic properties and magnetocaloric effect in Nd_xLa_(1-x)Fe_(11.5)Al_(1.5) compounds

Effects of Nd-doping on the magnetic properties and magnetocaloric effects （MCEs） of NdxLa1-xFe11.5Al1.5 have been investigated. Substitution of Nd leads to a weakening of the antiferromagnetic （AFM） coupling and an enhancement of the ferromagnetic （FM） coupling. This in turn results in a complex magnetic behaviour for Nd0.2La0.8Fe11.5Al1.5 characterized by the occurrence of two phase transitions at ～188 K （PM AFM） and ～159 K （AFM-FM）. As a result, a table-like MCE （9 J/kg.K） is found in a wide temperature range （160-185 K） for a field change of 0-5T around the transition temperature, as evidenced by both the magnetic and calorimetric measurements. Based on the analysis of low-temperature heat capacity, it is found that the AFM-FM phase transition modifies the electron density significantly, and the major contribution to the entropy change comes from the electronic entropy change.

X-Ray Diffraction Study of Carbon Nanotubes Under High Pressure

The structure and physical properties of carbon nanotubes have been investigated by using in situ high pressure energy dispersive x-ray diffraction with synchrotron radiation at pressures up to 50.7 GPa.At atmospheric pressure,the structure of carbon nanotubes is similar to the hexagonal close-packed lattice of graphite with the interplanar spacing of the diffraction line(002)d002=0.3404 nm and that of the line(100)d100=0.2116 nm.According to the high pressure x-ray diffraction results,the diffraction line(002)is broadened and weakened above 8 GPa,and carbon nanotubes become partly amorphous.When the pressures of 10 and 20 GPa are decreased down to zero,the diffraction line(002)is partly recovered.While at the maximum pressure of 50.7 GPa,they entirely become amorphous and this amorphous transition is irreversible.We used the equation of state of Birch-Murnaghan to fit the P-V data of carbon nanotubes and obtained the bulk modulus K0=54.3±3.2 GPa(at K'0=4.0).

Superconductivity of(R_(0.4)Pr_(0.6))_(0.5)Ca_(0.5)Ba_(2)Cu_(3)O_(7-δ)(R=La,Pr,Nd,Sm,Eu,Gd and Y)Prepared Under High Pressure

The nearly single phase(R_(0.4)Pr_(0.6))_(0.5)Ca_(0.5)Ba_(2)Cu_(3)O_(7-δ)compounds(R=La,Pr,Nd,Sm,Eu,Gd and Y)with Tc about 100 K were prepared under high pressure and high temperature using the cubic anvil apparatus.The Tc is much higher than that of the traditional R-123 superconductors without doping Ca on the rare-earth site.For various rare earths with different ionic radius,the(R_(0.4)Pr_(0.6))_(0.5)Ca_(0.5)Ba_(2)Cu_(3)O_(7-δ)compounds have almost the same critical temperature.This is different from the result of the ion-size effect of rare-earth ions in R1-xPrxBa2Cu3O7-δcompounds.Our results show that Pr has the same properties as other rare earths in the 123-phase compounds due to the doping of Ca.

Magnetic properties and magnetocaloric effect in compound PrFe_(12)B_6

Magnetic properties and magnetocaloric effect of compound PrFe12B6 are investigated. The coexistence of hard phase PrFe12B6 and soft phase α-Fe causes interesting phenomena on the curves for the temperature dependence of magnetization. PrFe12B6 experiences a first order phase transition at the Curie temperature 206 K, accompanied by an obvious lattice contraction, which in turn results in a large magnetic entropy change. The Maxwell relation fails to give the correct information about magnetic entropy change due to the first order phase transition nature. The large magnetic entropy changes of PrFe12.3B4.7 obtained from heat capacity method are 11.7 and 16.2 J/kg.K for magnetic field changes of 0-2 T and 0-5 T respectively.

Unit-Cell by Unit-Cell Epitaxial Growth of SrTiO_(3) and BaTiO_(3) Thin Films by Laser Molecular Beam Epitaxy

Atomically regulated unit-cell by unit-cell homoepitaxial SrTiO_(3) and heteroepitaxial BaTiO_(3) films were fabricated on SrTiO_(3)(100)substrates by laser molecular beam epitaxy.The fine streak patterns and more than 1000 cycles undamping intensity oscillation were obtained by in situ reflection high-energy electron diffraction with precisely controlled intermittence between each unit-cell layer.The surface morphology of the films was examined by atomic force microscopy.The root-mean-square surface roughness of the films is about 0.1 nm.

Preparation and Characterization of the New Superconductor MgB_(2)

Polycrystalline samples of the new superconductor MgB_(2) are prepared by solid state reaction using Mg and B powders.The resistance measurement shows that the onset transition temperature and zero resistance transition temperature are Tonsetc=43.8 K and Tc0=37 K,respectively.The Tc0 depends on measuring current strongly.The diamagnetic transition temperature of~38 K is obtained by the ac susceptibility measurement.X-ray powder diffraction spectra of MgB_(2) can be indexed using hexagonal structure with space group P6/mmm and lattice parameters a=0.30864 and c=0.35212 nm.A second phase,probably MgO,is also found.

Characterization of CoCrFeO_(4) Nanocrystals Prepared by a Sol-Gel Method

CoCrFeO_(4) nanocrystals have been synthesized using a sol-gel method.The specimen has an average grain size of 8.1 nm.The zero-field-cooled and field-cooled curves show a superparamagnetic transition occurring at a blocking temperature of TB≈249 K.The increase in coercivity of CoCrFeO_(4) nanocrystals with the decreasing temperature has been detected below the blocking temperature and could be explained by the Stoner-Wohlfarth theory.The temperature dependence of saturation magnetization shows that Bloch's law holds but with the Bloch exponent lower than the bulk value.