Spontaneous nuclear ferromagnetic ordering of in nuclei in AuIn2 Part I. Nuclear specific heat and nuclear susceptibility

We have measured the nuclear specific heat C_n and nuclear susceptibility _n of In nuclei (I=9/2, =5.5 _n) in the cubic intermetallic compound AuIn₂ (Korringa constant =0.11 Ksec) in the normal conducting state at 30K10mK and 2mTB115 mT. Our data show a positive nuclear Weiss temperature =+ 43 K and that the In nuclei undergo a nuclear ferromagnetic transition at T_c=35 K. The In nuclei experience an internal field of about 10 mT (obtained from C_n at T>T_c ). The nuclear ordering temperature T_c and the internal field increase with applied magnetic field. From the data we deduce exchange constants for the investigated system. The critical entropy reduction S(T_c)/S_max=8.6% and critical enthalpy E=0.28 RT_c are in reasonable agreement with the measured ordering temperature T_c,applying the Heisenberg model for a simple cubic I=9/2 spin system. The nuclear spin relaxation time calculated from the real and imaginary parts of _n is 10 msec at T>50 K, but drops to <1msec at T_c.This is the first observation of a spontaneous nuclear magnetic ordering transition in a not-hyperfine-enhanced metal at thermal equilibrium, i.e. at T _nuclear =T _electron .     

The use of industrial-grade platinum resistance thermometers between 77 K and 273 K

The stability and interpolation characteristics of some industrial-grade platinum resistance thermometers have been investigated between 77 K and 273 K. Seven sensors were thermally cycled many times between 77 K and 373 K and were found to suffer reversible changes in ice-point resistance. After some tens of cycles between 77 K and 273 K the ice-point resistances of the thermometers stabilised to within a few milliohms, provided that the thermometers were not heated above 300 K. A two-point calibration method for these thermometers is described. Using resistance values at the ice-point and the oxygen boiling point, a measurement accuracy of 35 mK can be obtained over the range 77 K to 273 K. Interpolation data for 27 thermometers are given.     

The use of international standards in the new national standard on the procedure for checking working resistance thermometers

Proposals for a new Russian standard on the procedure for checking working resistance thermometers, connected with changes in the international standards, in particular, in the last edition of the IEC 60751 standard, are considered. The need for a transition when checking from an estimate of the error to an estimate of the uncertainties is demonstrated. __________ Translated from Izmeritel’naya Tekhnika, No. 9, pp. 47–51, September, 2007.     

In-plane magnetic anisotropy and temperature dependence of switching field in (Ga, Mn) as ferromagnetic semiconductors

We explore the magnetic anisotropy of GaMnAs ferromagnetic semiconductor by Planar Hall Effect (PHE) measurements. Using low magnitude of applied magnetic field (i.e., when the magnitude H is smaller than both cubic Hc and uniaxial Hu anisotropy field), we have observed various shapes of applied magnetic field direction dependence of Planar Hall Resistance (PHR). In particular, in two regions of temperature. At T < Tc/2, the "square-shape" signal and at T > Tc/2 the "zigzag-shape" signal of PHR. They reflect different magnetic anisotropy and provide information about magnetization reversal process in GaMnAs ferromagnetic semiconductor. The theoretical model calculation of PHR based on the free energy density reproduces well the experimental data. We report also the temperature dependence of anisotropy constants and magnetization orientations. The transition of easy axis from biaxial to uniaxiale axes has been observed and confirmed by SQUID measurements.     

The roles of grain orientation and grain boundary characteristics in the enhanced superelasticity of Cu71.8Al17.8Mn10.4 shape memory alloys

Through texture and grain boundary control by continuous unidirectional solidification, the continuous columnar-grained polycrystalline Cu_71.8Al_17.8Mn_10.4 shape memory alloys were prepared and possess a strong 〈0 0 1〉 texture along the solidification direction and straight low-energy grain boundary. The alloys show excellent superelasticity of 10.1% improved from 3% for ordinary polycrystalline counterpart and with a tiny residual strain of less than 0.3% after unloading. There are some reasons for the enhanced superelasticity: (1) The martensitic transformation of all grains with strong 〈0 0 1〉-oriented texture occur at the same time under the tensile loading, which can avoid the significant stress concentration problem and transformation strain incompatibility at the grain boundaries due to the high elastic anisotropy in ordinary polycrystalline alloy. (2) High phase transformation strain can be obtained along 〈0 0 1〉 grain orientation. (3) Straight low-energy grain boundary and the absence of grain boundary triple junctions of continuous columnar-grained polycrystals can significantly reduce the blockage of martensitic transformation at the grain boundaries. These results provide a reference to structure design of high-performance polycrystalline Cu-based shape memory alloys.     

内压缩流程空分设备高压主换热器的开发与设计

介绍了为国产首套 10 0 0 0m3 h内压缩流程空分设备配套的高压主换热器的主要技术参数及结构设计特点 ,传热计算过程和结构尺寸的确定 ;通过整套空分开车运行后对高压主换热器各点温度及压力的实际测定 ,肯定了该套主换热器的设计及制造是成功的。     

The synthesis and characterisation of Co2X (Ba2Co2Fe28O46) and Co2U (Ba4Co2Fe36O60) ferrite fibres, manufactured from a sol-gel process

The X and U phases of hexagonal ferrites are notoriously difficult to make as pure materials, and what little data there is published regarding their physical or magnetic properties relates only to single crystals. Stoichiometric Co₂X and Co₂U fibres were made from a sol-gel based process, and the characteristics of the sols and fibres were studied using PCS, XRD, SEM and VSM. The evolution of the X and U fibres was studied, and shown to be similar that of the W and Z fibres whose structures they respectively resemble. Co₂X and Co₂U had been formed at 1200°C, and the morphology of the fibres was different from those of the W and Z phases. The magnetic properties, again while resembling the W and Z phases, were different to any of the other hexagonal ferrite fibres. The magnetic hysteresis loops of both fibres were magnetically as was, the Co₂X fibres having M _s = 45.0 emu g^–1 and H _c = 0.085 T, and the Co₂U fibres having M _s = 51.5 emu g^–1 and H _c = 0.059 T.     

The use of poly(acrylamide-acrylic acid)-montmorillonite composite for preparing low-activity 60Co, 65Zn, 134,137Cs mixed sealed source for radiometric calibration purposes

Poly(acrylamide-acrylic acid)-montmorillonite composite [P(AAm-MA)-M] was synthesized and used for preparing ⁶⁰Co, ⁶⁵Zn, ^134,137Cs mixed sealed source. The synthesis procedure was based on ??-induced polymerization of polyacrylamide (PAAm) in the presence of acrylic acid (AA), clay minerals (montmorillonite, M), and N,N??-methylenebisacrylamide (NMBA) as a cross-linker. The adsorbent functionality was assayed using FTIR spectroscopy and thermal analysis. The distribution coefficients of ⁶⁰Co(II), ⁶⁵Zn(II), and ^134,137Cs(I) ions on P(AAm-MA)-M were determined in relation to HCl concentration. P(AAm-MA)-M was loaded with ⁶⁰Co, ⁶⁵Zn, and ^134,137Cs by equilibrating it (0.5 g) with a mixed solution of ⁶⁰Co, ⁶⁵Zn, and ^134,137Cs at pH 3 (HCl) for 24 h at 25 ± 1°C. Mixed sealed source containing 5.3, 0.03, 0.05, and 1.05 ??Ci of ⁶⁰Co, ⁶⁵Zn, ¹³⁴Cs, and ¹³⁷Cs, respectively, was prepared by packing 100 mg of the loaded matrix in the cylindrical cavity of a Chinese Artelone capsule. The sealed source was subjected to quality control tests.