K.J. Lin

Measurement of heat capacity by fitting the whole temperature response of a heat-pulse calorimeter

A new method that fits the whole temperature response of a heat-pulse calorimeter for heat capacity is developed. Analyzing the thermal response of a heat-pulse calorimeter on a model that was used by the relaxation method, the authors derived some useful relations and further utilized the numeric method of the general linear least squares to determine the heat capacity of a sample. Absolute accuracy of the proposed method was verified by determining the heat capacity of a 0.249 76 g copper sample (purity 99.999%) on a self-designed and fully automated calorimetric system from 4.5 to 80 K. Comparing the result with the literature, the deviation in average was 1.2% from 4.5 to 20 K and 2.0% from 20 to 80 K. It is found that the proposed method is capable of measuring heat capacity regardless if the sample is adiabatically or nonadiabatically isolated. The size of the specimen is not critical for the application of the method and the temperature range of measurement can be expanded. It also deals with the τ...

Antiferromagnetism and mass-enhanced behavior in Ce2CuSi3

Temperature dependences of the specific heat, electrical resistivity and magnetic susceptibility of single-phased AlB2-type compound Ce2CuSi3 as well as its nonmagnetic counterpart La2CuSi3 are reported. La2CuSi3 is Pauli paramagnetic whereas Ce2CuSi3 shows complex magnetic properties. An antiferromagnetic ordering at 2.1 k is observed by low field (50 Oe) susceptibility measurement on Ce2CuSi3. Magnetic susceptibility measured under 2000 Oe, however, appears to be saturated below 2.1 K. Heat capacity measurement down to 4.5 K reveals an upturn in C(T) of Ce2CuSi3 which could be correlated with magnetic transition at 2.1 K. The electronic specific heat in Ce2CuSi3 is obtained, indicating an enhanced temperature-independent γ of 76mJK−2 mol−1 Ce. A negative contribution to the enhanced γ that could be due to spin fluctuation, is observed. The resistivity data of Ce2CuSi3 shows the typical behavior of a Kondo compound, which might be responsible for the enhanced effective mass.

Freezing and melting of gallium in porous glass

Abstract We report an investigation of the melting and the freezing of conducting materials confined in porous glass by electrical resistance measurements. For gallium in porous glass, heat-capacity measurements show a broadened latent-heat peak associated with the melting at about 230 K much lower than the bulk melting point 302.9 K. The resistance exhibits a clear freezing-melting hysteresis. For gallium in porous glass, in contrast to the freezing and the melting transitions the superconducting transition is extremely sharp and does not show any hysteresis during the cooling and warming process.

Magnetic ordering in UPd2Ge2

Abstract We present magnetic, electric and thermal properties of UPd2Ge2. In UPd2Ge2, a paramagnetic to antiferromagnetic transition is observed at 140 K. Below 100 K, the magnetization oscillates with temperature and the hysteresis loops exhibit ferromagnetic properties. The magnetic properties of UPd2Ge2 can be understood by incommensurate phases.

Spin-glass-like behaviour in UPd2Ge2

The magnetic susceptibility, hysteresis curves, ZFC and FC magnetic moments and magnetoresistance measurements indicate the appearance of a spin glass state in UPd2Ge2 below 87 K, and the existence of a ferromagnetic phase below 80 K. From these studies and taking into account the neutron diffraction data a mixed spin glass-ferro-antiferromagnetic state is suggested in the low-temperature region.

X-Ray Absorption Fine Structure Study in FeTiO3

X-ray absorption fine structure XAFS spectroscopy has been used to determine the valence system for the Fe atom in ilmenite, FeTiO3. This is the first XAFS data in FeTiO3 to our knowledge. The α-Fe2O3 data served as the standard in determining the ionization of the Fe atom in FeTiO3. Observation of intensity and k-space are consistent. There was no evidence of mixed valence on comparing the FeTiO3 near edge X-ray absorption spectrum with α-Fe2O3 data. The absorption spectra suggest that iron is in the trivalent state in ilmenite.

Magnetic properties and crystal-field effects in SmCuAl3

Abstract We present magnetic, electric and thermal properties of SmCuAl3. An antiferromagnetic transition is observed at 7 K. The hysteresis loops exhibit both ferromagnetic and antiferromagnetic properties at low temperature. SmCuAl3 displays large specific heat C(T) values at low temperatures. The specific heat C(T) is interpreted as a result of the small crystal-field splitting.