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1.
We report the influence of external high-pressure (P up to 8 GPa) on the temperature (T) dependence of electrical resistivity (ρ) of a Yb-based Kondo lattice, YbPd2Si2, which does not undergo magnetic ordering under ambient pressure condition. There are qualitative changes in the ρ(T) behavior due to the application of external pressure. While ρ is found to vary quadratically below 15 K (down to 45 mK) characteristic of Fermi-liquids, a drop is observed below 0.5 K for P=1 GPa, signaling the onset of magnetic ordering of Yb ions with the application of P. The T at which this fall occurs goes through a peak as a function of P (8 K for P=2 GPa and about 5 K at high pressures), mimicking Doniach's magnetic phase diagram. We infer that this compound is one of the very few Yb-based stoichiometric materials, in which one can traverse from valence fluctuation to magnetic ordering by the application of external pressure. 相似文献
2.
In order to investigate the pressure effect on the magnetism in the layered cobaltites, positive muon spin rotation and relaxation μ+SR experiments have been carried out up to 1.3 GPa using c-aligned polycrystalline samples of [Ca2CoO3]0.62[CoO2] and [Ca2Co4/3Cu2/3O4]0.62[CoO2]. A transverse field μ+SR experiment indicates that the transition temperature to an incommensurate spin density wave IC-SDW state is independent of hydrostatic pressure up to 1.3 GPa for the both compounds. Furthermore, there are no changes in the spontanious muon precession frequency in zero field at 5 K even under 1.3 GPa. These results strongly suggest that the IC-SDW exists not in the rocksalt-type block ([Ca2CoO3] and/or [Ca2Co4/3Cu2/3O4]) but in the CoO2 plane. 相似文献
3.
Elevation of the Power Factor of Co4Sb12 Skutterudite with Sm-Doping in High-Pressure High-Temperature Synthesis
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JIANG Yi-Ping JIA Xiao-Peng GUO Wei XU Hui-Wen DENG Le ZHENG Shi-Zhao MA Hong-An 《中国物理快报》2010,27(6):237-239
A thermoelectric material Smx Co4Sb12 (0( x ≤1.0) is synthesized at high pressure and high temperature leading to an enhanced power factor. The experimental measurements show that the SmxCo4Sb12 compounds exhibits n-type conduction. The absolute value of the Seebeck coefficient decreases with increasing Sm fraction. The resistivity increases with samarium content x from 0.1 to 0.2, but decreases dramatically when x changes from 0.2 to 1.0. The maximum power factor reaches 13.1 μW.cm^-1K-2 at x =1.0, which is larger than the data previously reported for the La-doped CoSb3 prepared at room pressure. 相似文献
4.
The spinel structure LiV2O4 is studied by local density approximation (LDA) as well as including strong correlation correction potential, i.e. the LDA+U scheme, which concerns the strongly correlated interaction. With LDA, the orbitals of V 3d and O 2p are well separated so that it presents purely metallic heavv fermion behaviour. The total energy of ferromagnetic phase is slightly lower than that of paramagnetic phase within the LDA ap- proach. This implies that the ferromagnetic instability as a consequence of spin frustrated magnetism can be observed in experiments. The strong correlation interaction by using LDA+U enhances the exchange splitting. The heavy-fermion feature can be derived from the sharp peak around the Fermi level from the density of states. 相似文献
5.
Cu Doping Effect on Electrical Resistivity and Seebeck Coefficient of Perovskite-Type LaFeO3 Ceramics
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WANG Hong-Chao WANG Chun-Lei ZHANG Jia-Liang ZHAO Ming-Lei LIU Jian SU Wen-Bin YIN Na MEI Liang-Mo 《中国物理快报》2009,26(10)
Perovskite-type LaFe1-xCuxO3 (x=0.10$, 0.14, 0.18) solid solution is prepared with the conventional solid-state reaction technique. The electrical resistivity and the Seebeck coefficient are measured in the temperature range 473-1073K to elucidate the Cu doping effect on the thermoelectric properties of the LaFeO3. The electrical resisitivity of LaFe1-xCuxO3 shows semiconducting behavior. The temperature dependence of the electrical resistivity indicates that the adiabatic small-polaron hopping mechanism is dominant for their electric transportations. The activation energy decreases with the increasing Cu content as well as the increasing temperature. The Seebeck coefficient changes from a negative value to a positive value around 510K, and increases with rising temperature up to 710K, then becomes saturated around 200μV/K. The Seebeck coefficient decreases with the substitution of Cu atoms in the temperature range of 573-1073K, while the electrical resistivity decreases with the substitution of Cu atoms in the whole measured temperature. Overall the power factor increases with rising temperature, and the highest value of power factor is 54μW/K2m for x=0.10 of Cu doping. 相似文献
6.
M.A. Mojumder 《Physica B: Condensed Matter》2009,404(16):2455-2460
We have clarified the ‘hidden order’ of URu2Si2, and the spin density wave, and calculated the large entropy loss on Kondo channel transition to the one channel Kondo fixed point of the crystal. The three collective excitations, particularly the one discovered recently, have been either derived or explained. These and other findings, in excellent agreement with outstanding data, are of general applicability to the analogues of URu2Si2 including the nonstoichiometric cuprates. The results show the presence of multichannel Kondo effect in these crystals. 相似文献
7.
W.Y. Zhang Z.P. Guo L. Cui X.P. Zhang Y.G. Shi T.Y. Zhao 《Solid State Communications》2005,135(8):480-484
Effect of Ti doping on the electrical transport and magnetic properties of layered Na0.8Co1−xTixO2 compounds has been investigated. The lattice parameters a and c increase with x. A minor amount of Ti doping results in a metal-insulator transition at low temperatures. For samples with x>0.03, the variable-range hopping process dominates the transport behavior above a certain temperature. The temperature dependence of magnetization of all the samples is found to obey the Curie-Weiss law. The mechanism of the doping effect is discussed. 相似文献
8.
Z. Kletowski 《Solid State Communications》2006,137(11):634-636
Results of the thermoelectric power (TEP) measurements done on monocrystalline samples of RESn3 compounds (RE=La, Pr, Nd, and Gd) are presented for the temperature range of 5.5-300 K. It was found that the TEP is positive and weakly temperature dependent at temperatures T>100 K. For T<100 K pronounced anomalies have been observed for the PrSn3 and the NdSn3 compounds in the vicinity of 10 K.We argue that the Kondo and crystal field effects cause these anomalies. A shape of the TEP anomaly found for PrSn3 resembles very much that observed in the electrical resistivity. 相似文献
9.
Low-temperature specific-heat measurements on YbRh2Si2 at the second order antiferromagnetic (AF) phase transition reveal a sharp peak at TN=72 mK. The corresponding critical exponent α turns out to be α=0.38, which differs significantly from that obtained within the framework of the fluctuation theory of second order phase transitions based on the scale invariance, where α?0.1. We show that under the application of magnetic field the curve of the second order AF phase transitions passes into a curve of the first order ones at the tricritical point leading to a violation of the critical universality of the fluctuation theory. This change of the phase transition is generated by the fermion condensation quantum phase transition. Near the tricritical point the Landau theory of second order phase transitions is applicable and gives α?1/2. We demonstrate that this value of α is in good agreement with the specific-heat measurements. 相似文献
10.
Junfeng Wang Di Yin Zhengyou Liu Decheng Tian Yuheng Zhang 《Solid State Communications》2004,132(10):653-656
The thermoelectric power (TEP) of the quasi-one-dimensional charge-density-wave (CDW) conductors rubidium blue bronze Rb0.3MoO3 and its alloy Rb0.15K0.15MoO3 were measured in the temperature range 80-280 K. The result showed a sign change from a small positive value to a great negative value where the Peierls transition temperatures (Tp) are 183 and 180 K for Rb0.3MoO3 and Rb0.15K0.15MoO3, respectively. Above Tp, the TEP for both samples can be described with the empirical relation S=AT+B; while below Tp, the TEP fits well the relation S=AT+B/T based on the experimental data. The Fermi energies εF for Rb0.3MoO3 and Rb0.15K0.15MoO3 are estimated to be 1.55 and 0.53 eV, respectively. 相似文献
11.
The thermoelectric properties of Bi intercalated compounds BixTiS2 have been investigated at the temperatures from 5 to 310 K. The results indicate that Bi intercalation into TiS2 leads to substantial decrease of its electrical resistivity (one order low for x=0.05 and two orders low for x=0.15, 0.25 at 300 K) and lattice thermal conductivity (22, 115 and 158% low at 300 K for x=0.05, 0.15 and 0.25, respectively). Specially, the figure of merit, ZT, of lightly intercalated compound Bi0.05TiS2 has been improved at all temperatures investigated, and specifically reaches 0.03 at 300 K, which is about twice as large as that of TiS2. 相似文献
12.
D. Baldomir V. Pardo S. Blanco-Canosa D.I. Khomskii A. Piñeiro J.E. Arias 《Journal of magnetism and magnetic materials》2009,321(7):679-681
Electronic structure calculations were performed for ZnV2O4, a material close to a metal-insulator transition. Structural optimization leads to the formation of V-V dimers along the off-plane chains. A strong spin-lattice coupling is expected close to the transition to itinerancy. No orbital ordering is observed in such a structure, and the experimentally found magnetic structure is naturally explained. 相似文献
13.
V. Varadarajan 《Solid State Communications》2007,141(7):402-406
We have measured the specific heat of crystals of (Ca1−xSrx)3Ru2O7 using ac- and relaxation-time calorimetry. Special emphasis was placed on the characterization of the Néel () and structural () phase transitions in the pure, x=0 material. While the latter is believed to be first order, detailed measurements under different experimental conditions suggest that all the latent heat (with L∼0.3R) is being captured in a broadened peak in the effective heat capacity. The specific heat has a mean-field-like step at TN, but its magnitude () is too large to be associated with a conventional itinerant electron (e.g. spin-density-wave) antiferromagnetic transition, while its entropy is too small to be associated with the full ordering of localized spins. The TN transition broadens with Sr substitution while its magnitude decreases slowly. On the other hand, the entropy change associated with the Tc transition decreases rapidly with Sr substitution, and is not observable for our x=0.58 sample. 相似文献
14.
Charge trapping characteristics of the metal-insulator-silicon (MIS) capacitors with Si02/HfO2//A12O3 stacked dielectrics are investigated for memory applications'. A capacitance-voltage hysteresis memory window as large as 7.3 V is achieved for the gate voltage sweeping of ±12 V, and a fiat-band voltage shift of 1.5 V is observed in terms of programming under 5 V and I ms. Furthermore, the time- and voltage-dependent charge trapping characteristics are also demonstrated, the former is related to charge trapping saturation and the latter is ascribed to variable tunnelling barriers for electron injecting and discharging under different voltages. 相似文献
15.
Doubly substituted polycrystalline compound bulk samples of BaxAgyCa2.8Co4O9 were prepared via citrate acid sol-gel method followed by spark plasma sintering. The phase composition, orientation, texture and high temperature electrical properties were systematically investigated. The results showed that the orientation and the texture could be modified by altering ratio of Ba to Ag. The resistivity and the Seebeck coefficient of substituted samples were decreased by decreasing Ba/Ag ratio except for that of Ba0.1Ag0.1Ca2.8Co4O9 sample with lowest electrical resistivity (7.2 mΩ cm at 973 K), moderately high Seebeck coefficient (172 μV/K at 973 K) and improved power factor (0.42 mW/mK2 at 973 K). 相似文献
16.
We studied, strongly correlated states in triangular artificial atoms. Symmetry-driven orbital degeneracy of the single particle states can give rise to an SU(4) Kondo state with entangled orbital and spin degrees of freedom, and a characteristic phase shift δ=π/4. Upon application of a Zeeman field, a purely orbital Kondo state is formed with somewhat smaller Kondo temperature and a fully polarized current through the device. The Kondo temperatures are in the measurable range. The triangular atom also provides a tool to systematically study the singlet-triplet transitions observed in recent experiments [Phys. Rev. Lett., 88 (2002) 126803, cond-mat/0208268 (2002)]. 相似文献
17.
Z.C. Xia Y. Wang H.R. Zeng Q.X. Zhou M.T. Hu B. Dong G. Liu X.N. Feng L. Liu S.L. Yuan C.Q. Tang 《Solid State Communications》2006,137(4):216-220
The electrical transport and magnetic properties of high Bi doped (La0.73Bi0.27)0.67Ca0.33MnO3 are studied at the temperature and magnetic field ranges from 10 to 300 K and 0 to 3 T. Significant temperature and magnetic field hystereses are observed in both resistivity and magnetization measurements. Meanwhile, an enhanced magnetoresistance effect, within a wide temperature window, is obtained in the (La0.73Bi0.27)0.67Ca0.33MnO3. The hysteresis and enhanced magnetoresistance are discussed based on an inhomogeneous metastable structure related to the Bi dopant. 相似文献
18.
H.X. Yang 《Solid State Communications》2007,142(12):718-722
The ground state of Na0.5CoO2 has been calculated using the full potential local orbital method and local density approximation plus Hubbard U (); the results demonstrate that charge and orbital ordering evidently exist in the present system in association with the antiferromagnetic state. Notable structural features observed between 300 and 30 K have been carefully examined using in situ TEM investigations, a superstructure with a wave vector of Q1=a∗/2, becoming commonly visible below , can be interpreted as the charge/orbital ordering on the Co1 and Co2 sites. Moreover, we have also observed another notable superstructure with Q2=a∗/4 below the phase transition of , which suggests a more complicated orbital ordered state existing at lower temperatures. 相似文献
19.
20.
Cluster based analysis show that the observable three-level YbB12 spin excitations character can be reproduced in the framework of the asymmetric variant of periodic Anderson model with a singlet ground state and two electrons per site. For the macroscopic system the effective Hamiltonian with the direct f-f exchange is justified and the dynamic spin susceptibility of f-electrons is found. It is shown that the lowest spin excitation dispersion has minimum at the antiferromagnetic vector as observed in the experiment. The distinctive feature of analysis is the using of singlet and triplet basis operators. 相似文献