Low temperature normal state resistance of ternary molybdenum sulfides

The resistance varies as T² over the range of T from T_c to nearly 40 K, in sintered, sputtered and evaporated thin film Cu_xMo₆S₈, and in sputtered PbMo₆S₈ films. In sintered PbMo₆S₈ the resistance varies as T. These results can neither be explained by existing theory for PbMo₆S₈, nor by a Mo₂S₃ phase argument.     

Low temperature magnetization measurements on heavy rare earth molybdenum sulfides, (RE)1.2Mo6S8

Magnetization measurements on the heavy rare earth molybdenum sulfides, (RE)_1.2Mo₆S₈ (RE = Gd, Tb, Dy and Ho) were performed to further clarify the natures of their magnetic orders found in our recent resistivity and ac susceptibility measurements below 1 K. The variations of their magnetic and superconducting transition temperatures along the series of the rare earth ions in the Periodic Table are interpreted by means of available theories.     

Low temperature heat capacity of Rh-Cu alloys

Reported here are the low temperature heat capacity data on a series of single phase fcc Rh-Cu alloys. The electronic heat capacity coefficient, γ, decreases rapidly up to 20 at % of copper in Rh and then stays constant to ～60 at % Cu after which decreases smoothly to the pure Cu value. This is interpreted as due to the initial partial filling of the d-band after which the conduction electron of Cu goes into the s-band. An attempt is made to understand the origins of the curious anomalies in the Debye temperature and microhardness data.     

Low temperature heat capacity of electrotransported scandium

The heat capacity of two scandium samples containing 1.6 and <5 ppm atomic Fe was measured from 1 to 20 K. The weighted values for γ and θ_D are: 10.340 ± 0.018 mJ/g-at. K² and 346.1 ± 0.9 K, respectively. This is the first time anyone has obtained the same heat capacity results on two different scandium samples. The iron impurity concentration appears to be critical.     

Low temperature heat capacity of TTF (TCNQ)

Low temperature heat capacity measurements of two TTF (TCNQ) polycrystalline samples are reported. The existence of a linear term and an anomolously high Debye temperature for one of them at low temperatures are attributed to impurity effects. The literature data on other (TCNQ) salts are discussed.     

Low temperature resonances in the electron heat capacity of finite systems

Temperature variations of the heat capacity (C) are studied in a low temperature regime T<δ_F∼ε_F/N for 2D and 3D systems with N∼10²-10⁴ treated as a canonical ensemble of N-noninteracting fermions. The analysis of C is performed by introducing the function φ(ε), the spectral distribution of C, that gives the contribution of each single-particle state to C. This function has two peaks divided by the energy interval . If at some temperature T_res a resonance takes place i.e. the positions of these peaks coincide with energies of two levels nearest to ε_F then C vs T can show a local maximum at T_res. This gives us the possibility to assess the single-particle level spacings near the Fermi level.     

Low temperature heat capacity of YBa2Cu3O7

We have measured the heat capacity of superconducting, single phase YBa₂Cu₃O₇ in the temperature range 2 to 18 K. An extrapolation of the data between 4 and 9 K gives aC/T (T → 0) of ∼ 25 mJ/mole K². The Debye temperature obtained from the high temperature linear portion ofC/T vsT ² plot is 325 K.     

Antiferromagnetic ordering in terbium dihydride. Low temperature heat capacity studies

The specific heat of terbium dihydride, TbH_2.01, was measured in the temperature range from 4–200 K. An extremely sharp λ-type specific heat anomaly due to an antiferromagnetic transition has been found at T_N = 16.06 ± 0.01 K.     

Low temperature heat capacities of DyConi

Heat capacity data are presented for DyCoNi in the temperature range 4.2 to 300 K. The sample exhibits an anomaly peaking at 63 K. This is interpreted as arising from ferromagnetic ordering. Resistivity measurements also indicate an anomaly at 63 K. The magnetic entropy, evaluated by using the heat capacity data of LaNi₂ as “a blank” ins nearly R in 4. These results are interpreted on the basis of an accidental four-fold degeneracy of the ground state of the Dy³⁺. The itinerant nature of the cobalt moment proposed by Taylor et al. appears to be valid in this compound.     

Low temperature specific heat of ErAs

The specific heat of a sintered sample of ErAs has been measured from 1.4–6.1 K. A single broad κ-like peak in the data occurs at 3.25K. The entropy associated with the peak is approximately R ln4 suggesting an $\text{S′ =}\text{3}\text{2}$ ground state.     

The temperature dependence of nanocrystal heat capacity

The temperature dependence of the specific (per atom) entropy and heat capacity of a nanocrystal is studied using a nanocrystal model in the form of a rectangular parallelepiped with variable surface shape. Accounting for the temperature dependence of the surface energy showed that the temperature dependence of the surface contribution to specific entropy is described by the same function that determines the temperature dependence of the isochoric heat capacity of a macrocrystal. Thus, at T → 0 K at T/Θ > 2 the surface contribution to the specific heat is zero. The maximal surface contribution to specific heat is reached at T/Θ = 0.2026 and is equal to c _st/k _B = 1.0115 (where k _B is the Boltzmann constant, Θ is the characteristic temperature depending both on the size and the shape of the nanocrystal). The applicability of the Grüneisen rule for a nanocrystal both at low and high temperatures is studied. It has been found that a case when the surface contribution to specific heat would be negative c(N) < c(∞), i.e. c _st(N) < 0 can occur for nanocrystals with a noncubic habitus.     

Low temperature heat capacity and magnetic study of the Al80Mn20 icosahedral alloy

Low temperature heat capacity and magnetization measurements are reported for the Al₈₀Mn₂₀ alloy in the quasicrystalline icosahedral phase. The heat capacity, which was measured for temperatures ranging from 0.5 to 5.0 K and magnetic fields up to 11.7 kOe, shows a broad magnetic contribution around 1.0 K. The linear electronic contribution does not indicate an anomalously high density-of-states at the Fermi energy as predicted theoretically for quasicrystalline systems. The d.c. magnetization, which was measured from 2.0 to 300 K and with magnetic fields up to 50 kOe, indicates an effective number of one 11 μ_B localized magnetic moment for approximately every 100 Mn atoms. The low field susceptibility follows the Curie-Weiss law for temperatures ≧ 10 K, while a spin-glass-like ordering is observed at low temperatures.     

Low temperature specific heat of Cr-Fe-Si alloys

Low temperature specific heats of Cr-Fe-Si alloys with 3 at. % Si were investigated between 1.4°–4.2°K. The electronic specific heat coefficient γ essentially varies with transition metal electron concentration ( e/a) in the same manner as the Cr-Fe alloys but with the high γ peak slightly shifted to lower e/a. The shift of γ peak suggests transfer of electrons from Si atoms to the 3d magnetic subband of the transition elements.     

Low temperature solventless syntheses of nanocrystalline nickel sulfides with different sulfur sources

This work describes a novel synthesis for the production of very pure nanocrystalline hexagonal nickel sulfide phase (h-NiS) by the solventless route in air at temperatures of only 190 °C. Only the cubic NiS₂ nickel sulfide phase is obtained when the sulfur source reacting with the nickel acetate powder (NiAc) is switched from thiourea (TU) to elemental sulfur (S_N). When using both TU and S_N sulfur sources, phase mixture of h-NiS, NiS₂ and Ni₃S₄ with less aggregated particles was obtained. Relative concentrations of the phases were quantified by the Rietveld refinement of the XRD powder patterns. The thermal evolution of stoichiometric reagents mixture was observed by TG-FTIR and DSC curves.     

Multiple phase transitions in rare earth tetraborides at low temperature

We report the temperature dependence of the magnetic susceptibility of single crystals of PrB₄, GdB₄, TbB₄, HoB₄ and TmB₄, both parallel and perpendicular to the tetragonal c-axis. We also present low temperature resistance measurements on crytals of GdB₄ through TmB₄. Two magnetic phase transitions are found for TbB₄, DyB₄, HoB₄ and TmB₄. For the latter two compounds, the lower transitions appear to be first order. For HoB₄, we have measured the low temperature specific heat. The lower transition in TbB₄ and HoB₄ is rapidly depressed upon dilution with YB₄.     

Low temperature heat capacity of LaRu2 by a.c. technique

The low temperature heat capacity data of a small bulk sample of LaRu₂ show that the structural transformation occurring at T_m ～ 29.5K is rather spread out. The electronic heat capacity coefficient, γ, and Debye temperature, θ_D, are found to be respectively $\text{8.5}\text{mJ}\text{g}$. atom K² and 164 K. The multiple anomalies below T_m and T_c (4.45 K) are discussed.     

Room temperature magnetization measurements of some substituted rare earth iron garnets

The saturation magnetization (M _s) and the initial magnetic susceptibility (χ _in) of substituted yttrium iron garnet (YIG) Ho_3−x Y _x Fe₅O₁₂ where (x=0,0.3,1.5), pure terbium iron garnet Tb₃Fe₅O₁₂, and substituted aluminum iron garnet (AlIG) Ho₃Fe_5−x Al _x O₁₂ where (x=0.05,0.7) at room temperature are reported. It has been observed that M _s and χ _in decrease in a linear manner as Ho³⁺ replaces Y³⁺ in yttrium iron garnet. For substituted (AlIG), a drastic decrease in both M _s and χ _in as Al³⁺ ions replace Fe³⁺ ions. The rate of decrease of M _s and χ _in with the increase of Al³⁺ for substituted (AlIG) is greater than that for substituted (YIG). That is attributed to the decrease in the superexchange interaction (self and mutual iron interactions) with Al substitution.     

Normal state properties of the ternary molybdenum sulfides

By making a large number of normal state and superconducting properties measurements, all on the same ternary molybdenum sulfide samples, we obtain values for Fermi surface and superconducting parameters. From these we conclude that sputtered ternary molybdenum sulfides are not completely in the dirty superconductor limit, and that they are d-band metals with a high electron carrier density.     

Low threshold fiber taper coupled rare earth ion-doped chalcogenide microsphere laser

We report the applications of a low-cost and environmentally friendly chalcogenide glass, 75 Ge S2-15Ga2S3-10 Cs I,in building active microsphere laser oscillators. A silica fiber taper is used as the coupling mechanism. With an 808-nm laser diode as a pump source, we show that a high-Q(～ 6×104) laser mode could be obtained from a 75-μm diameter microsphere that is coupled with a 1.77-μm waist-diameter fiber taper. The threshold of the incident pump power is1.39 m W, which is considerably lower than those of previously reported free-space coupled chalcogenide microsphere lasers. We also note an apparent enhancement in laser power generated from this chalcogenide microsphere laser.     

Susceptibility,electronic specific heat and magnetization of mixed-valent rare earth compounds

Applying our previous theory for mixed-valent materials, we report calculations of susceptibility, specific heat and magnetization of α-Ce, CePd₃, YbAl₃ and YbCuAl. The results are compared with experiment.