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1.
We report the low temperature magnetic properties of Cd-doped single crystals of Ce2RhIn8 grown from In-flux. Measurements of temperature-dependent magnetic susceptibility, heat capacity, electrical resistivity and X-ray magnetic scattering revealed that Cd-doping enhances the antiferromagnetic ordering temperature from for crystals with nominal Cd-concentration of ~20%. Similarly to the pure compound, Cd-doped Ce2RhIn8 presents just below TN a commensurate antiferromagnetic structure with a propagation vector . Comparisons between our results and the general effects of Cd-doping on the single layer related family CeMIn5 (M=Co, Rh and Ir) will also be given.  相似文献   

2.
We have investigated the crystallographic, magnetic and thermodynamic properties of the as-cast and annealed Ce2NiSi3 alloys, crystallizing in the AlB2-type hexagonal structure. The DC-magnetic susceptibility data show that the as-cast sample exhibits an antiferromagnetic (AFM) ordering below TN= 3.8 K, whereas the annealed sample shows, at 4.2 K, a magnetic transition of AFM nature and, around 2.5 K, an additional anomaly. The specific heat shows a peak with at 3.8 K for the as cast sample, which shifts to lower temperatures when the magnetic field increases, consistent with the antiferromagnetic nature of the transition. On the other hand, in the annealed alloy, the maximum of the specific heat peak reaches at 4.2 K, and no additional anomalies were observed. The different magnetic behavior between the as-cast and annealed samples is attributed to thermal effects on the structural disorder of nickel and silicon atoms, as already observed in other isotypic R2TSi3 alloys, where R=U or Ce, and T= transition metal.  相似文献   

3.
Low temperature magnetic (M) and thermal (CP) properties of the intermetallic compound Ce2Pd2Sn have been investigated at zero and different magnetic fields. Two transitions were recognized at and , with latter nearly coinciding with the extrapolated Curie-Weiss temperature . The Curie factor evaluated from TTM, is ≈2μB. The positive value of θP, the triangular coordination of the magnetic (Ce) atoms and the weak effect of applied magnetic field, reveal that TM cannot be considered as a canonic antiferromagnetic transition like claimed in the literature. M(T) measurements under moderate magnetic fields () show TC(B) increasing while TM(B) is practically not affected. Both transition merge in a critical point at for , where the intermediate phase is suppressed. At , the cusp of a first order transition is observed in CP(T). According to the proposed ferromagnetic ground state, it is followed by a CP(T)∝T3/2exp(-Eg/T) dependence, with a gap of anisotropy .  相似文献   

4.
This work reports the ultraviolet absorption spectrum and cross-sections of ethynyl (C2H) radicals in the wavelength range 235-260 nm, determined at T=298 K and at a total pressure of about 20 kPa (150 Torr). Ethynyl radicals were produced from the single photon 193 nm excimer laser photolysis of dilute mixtures of C2HCF3 or C2H2 in He. Gas chromatographic/mass spectroscopic analysis of the photolyzed samples showed diacetylene (C4H2) as the major stable product. Addition of methane in the photolysis mixtures resulted in reduction of diacetylene and production of methylacetylene and ethane, products of the reaction of ethynyl radicals with methane. Survey of the ultraviolet spectral region, employing time-resolved UV-absorption spectroscopy, resulted in detection of a transient absorption centered at about 243 nm. The spectra obtained from the 193-nm photolysis of both C2HCF3/He and C2H2/He radical precursors were nearly identical, suggesting that the absorption feature can be attributed to the ethynyl radicals. The observed ultraviolet spectrum exhibits a relatively broad absorption feature with some structures and an absorption peak at about 243.5 nm. The absorption cross-sections for ethynyl radicals have been determined in this work for the first time. The C2H cross-section, at the maximum absorption, at 243.5 nm is . The stated uncertainty includes the random and systematic measurement errors. The UV absorption feature, detected in this work, can be assigned to the transitions from the ground electronic state and also possibly from coupled ground and lowest electronic states to the electronic state B (or 32A′) of C2H. This assignment is based on previously reported high level ab initio molecular orbital calculations and results of recent laser-induced fluorescence studies of the ethynyl radical.  相似文献   

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The rotationally resolved vibronic bands in the forbidden electronic transition of the cumulene carbene C3H2 have been observed in the gas phase by cavity ring down absorption spectroscopy through a supersonic planar plasma with allene as precursor. The band detected in the 16 223 cm−1 region is a result of vibronic interaction and is assigned to a combination of a1 and b2 vibrations with a frequency around 2250 cm−1. Another vibronic band near 15 810 cm−1 has an unusual rotational structure because the Ka = 0-1 subband is absent. It is assigned to a combination of a1 and b1 vibrations, ∼1850 cm−1, which borrow intensity from the near lying state due to a-type Coriolis coupling. A rotational analysis using a conventional Hamiltonian for an asymmetric top molecule yields molecular constants for the vibrational excited levels of the Ã1A2 state, which were used for the determination of the geometry. The stronger transition of C3H2, measured in a neon matrix in the 16 161-24 802 cm−1 range, was not detected. The reason for this is a short lifetime of the state, leading to line broadening.  相似文献   

7.
8.
Magnetic susceptibility obtained from magnetization measurement (for fields H=0.1 and 1.0 T) of polycrystalline Eu2Ti2O7 shows two distinct features. Firstly, increases on cooling below 300 K and attains a temperature-independent constant value at 68 K (Tmax). Secondly, shows an antiferromagnetic increase below 4.9±0.1 K. The former behavior is explained by crystal field (CF) theory. CF levels and wave functions of ground and excited states are determined accurately from analyses of and earlier reported Mössbauer and optical spectra. Analysis of vs. 1/T curve at low temperatures gives the classical nearest-neighbor exchange interaction Jcl=−0.76 K and a weak dipolar interaction Dnn=0.0056 K. CP of polycrystalline sample of Eu2Ti2O7 and Y2Ti2O7 are measured between 1.8-35 and 1.8-120 K respectively and θD vs. T (K) curves are calculated. At 4 K, θD of Eu2Ti2O7 shows a kink and dCP/dT curve show a maximum. Optical results show energy exchange between Eu3+ ions at intrinsic and extrinsic (defect) sites via super-exchange interaction at low temperature which may account for the observed anomalous behavior of and CP.  相似文献   

9.
10.
We report radio-frequency (rf) electrodynamics in polycrystalline La0.67Ba0.23Ca0.1MnO3 as a function of temperature and magnetic field using a home-built LC resonant circuit powered by an integrated chip oscillator. The resonance frequency (fr) of the oscillator and the power (P) absorbed by the sample are measured simultaneously. The paramagnetic to ferromagnetic phase transition in the absence of an external magnetic field is accompanied by a rapid decrease in both P and fr around the Curie temperature TC=300 K. However, much below TC, the fr shows a step-like anomaly around 165 K (195 K) while cooling (warming), which we attribute to a structural phase transition from high temperature rhombohedral () to low temperature orthorhombic (Imma) phase. The step-like anomaly in fr versus T disappears in a field of 300 G. Fractional changes as large as 19% in Δfr/fr and 10% in ΔP/P are observed under H=1 kG around TC. Our study suggests that the rf resonance technique is a versatile tool to study the magnetization dynamics as well as to investigate the structural phase transition in manganites.  相似文献   

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14.
The phase relation of LaFe11.5Si1.5 alloys annealed at different high-temperature from 1223 K (5 h) to 1673 K (0.5 h) has been studied. The powder X-ray diffraction (XRD) patterns show that large amount of 1:13 phase begins to form in the matrix alloy consisting of α-Fe and LaFeSi phases when the annealing temperature is 1423 K. In the temperature range from 1423  to 1523 K, α-Fe and LaFeSi phases rapidly decrease to form 1:13 phase, and LaFeSi phase is rarely observed in the XRD pattern of LaFe11.5Si1.5 alloy annealed at 1523 K. With annealing temperature increasing from 1573  to 1673 K, the LaFeSi phase is detected again in the LaFe11.5Si1.5 alloy, and there is La5Si3 phase when the annealing temperature reaches 1673 K. There almost is no change in the XRD patterns of LaFe11.5Si1.5 alloys annealed at 1523 K for 3-5 h. According to this result, the La0.8Ce0.2Fe11.5−xCoxSi1.5 (0≤×≤0.7) alloys are annealed at 1523 K (3 h). The analysis of XRD patterns shows that La0.8Ce0.2Fe11.5xCoxSi1.5 alloys consist of the NaZn13-type main phase and α-Fe impurity phase. With the increase of Co content from x=0 to 0.7, the Curie temperature TC increases from 180 to 266 K. Because the increase of Co content can weaken the itinerant electron metamagnetic transition, the order of the magnetic transition at TC changes from first to second-order between x=0.3 and 0.5. Although the magnetic entropy change decreases from 34.9 to 6.8 J/kg K with increasing Co concentration at a low magnetic field of 0-2 T, the thermal and magnetic hysteresis loss reduces remarkably, which is very important for the magnetic refrigerant near room temperature.  相似文献   

15.
The 133Cs 1/2→−1/2 spin-lattice relaxation rate, , and the spin-spin relaxation rate, , for a Cs2CaCl4·2H2O single crystal have been measured in function of temperature. The dominant relaxation mechanism of this crystal over the whole temperature range investigated here proceeds via quadrupole interaction. The changes in the 133Cs spin-lattice relaxation rate near 325 K (=Tc1) and 360 K (=Tc2) correspond to phase transitions in the crystal. The change in the spin-lattice relaxation rate at Tc1 is small because the crystal lattice does not change very much during this phase transition. The change in near Tc2 is due to the critical slowing down of the soft mode that typically occurs in structural phase transitions. The temperature dependence of the spin-lattice relaxation rate for this crystal has maximum values at about 240 K, which is attributable to the effect of molecular motion as described by Bloembergen-Purcell-Pound theory. The phase transition temperatures Tc1 and Tc2 obtained from the temperature dependence of the relaxation rate is also clear from data obtained using differential scanning calorimetry. Therefore, we know that previously unreported phase transitions occur at 325 and 360 K.  相似文献   

16.
Rotationally resolved electronic spectrum of the origin band in the 2A″-X2A″ transition of a nonlinear carbon chain radical C6H4+ has been recorded in the 604 nm region using cw cavity ring down spectroscopy. The radical was produced by a discharge through an acetylene-helium mixture in a supersonic planar expansion. The rotational structure has been analysed and precisely determined. A band having a-type prolate rotational structure has also been observed near 581 nm. By considering the results of ab initio calculations this band is assigned to a transition involving the excitation of the ν12 fundamental in the upper 2A″ electronic state of the same C6H4+ isomer.  相似文献   

17.
BiMnO3 thin films were deposited by means of rf-sputtering onto [1 0 0] oriented SrTiO3 substrates. X-ray diffraction measurements revealed epitaxial growth with [0 0 l]m orientation in the monoclinic structure representation, equivalent to the direction of the pseudocubic cationic lattice. This [0 0 l]m orientation was obtained in a wide deposition parameters range. Preliminary magnetization measurements suggest that these films do not present ferromagnetism below the bulk Curie temperature, TC=105 K.  相似文献   

18.
The luminescence properties of Ce3+ and Tb3+ in Y3Si2O8Cl have been investigated. The Ce3+ excitation bands in the region from 220 to are attributed to the transitions from 4f level to the crystal-field splitting levels of 5d. The Tb3+ excitation bands in the region from 220 to are due to the 4f-5d transitions. The spectral energy distributions of Tb3+ emission strongly depend on the Tb3+ concentration, the emissions of Tb3+ decrease with increasing Tb3+ concentration, this phenomenon is due to the cross-relaxation between Tb3+ ions. The efficient energy transfer from Ce3+ to Tb3+ in the Y3Si2O8Cl is observed and discussed.  相似文献   

19.
Spectral absorption cross-sections, kν (), have been measured in the 8.0 and bands of C2F6. Temperature and total (N2-broadening) pressure have been varied to represent the conditions specified in various models of the terrestrial atmosphere so that the absorption cross-sections can be applied directly to the optical remote-sensing of C2F6 in the atmosphere. The measured absolute intensities of the 8.0 and the bands are (1.636±0.003)×10−16 and (, respectively.  相似文献   

20.
We have carried out specific heat measurements on EuIn2P2 at high magnetic fields perpendicular to the c-axis in the hexagonal crystal structure in order to understand its thermal properties. The temperature dependence of the specific heat exhibits a clear λ-type anomaly due to a magnetic transition at , indicating that the magnetic transition is of second-order. The λ-type anomaly becomes markedly broader with increasing the magnetic field. This remarkable field-dependence is consistent with the results of previous magnetization measurements which suggest that Eu2+ magnetic moments align ferromagnetically perpendicular to the c-axis below TC. In addition, a hump in the specific heat is observed around 7 K, which can be ascribed to the Zeeman splitting of the Eu2+ multiplet by internal magnetic fields.  相似文献   

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