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J. M. Dai

Publications and source records attributed to J. M. Dai.

12 recordsLinked to original sources
arXiv2009

Superconductivity and single crystal growth of Ni0:05TaS2

Superconductivity was discovered in a Ni0:05TaS2 single crystal. A Ni0:05TaS2 single crystal was successfully grown via the NaCl/KCl flux method. The obtained lattice constant c of Ni0:05TaS2 is 1.1999 nm, which is significantly smaller than that of 2H-TaS2 (1.208 nm). Electrical resistivity and magnetization measurements reveal that the superconductivity transition temperature of Ni0:05TaS2 is enhanced from 0.8 K (2H-TaS2) to 3.9 K. The charge-density-wave transition of the matrix compound 2H-TaS2 is suppressed in Ni0:05TaS2. The success of Ni0:05TaS2 single crystal growth via a NaCl/KCl flux demonstrates that NaCl/KCl flux method will be a feasible method for single crystal growth of the layered transition metal dichalcogenides.

cond-mat.supr-con↗
arXiv2009

The observation of a positive magnetoresistance and close correlation among lattice, spin and charge around TC in antipervoskite SnCMn3

The temperature dependences of magnetization, electrical transport, and thermal transport properties of antiperovskite compound SnCMn3 have been investigated systematically. A positive magnetoresistance (~11%) is observed around the ferrimagnetic-paramagnetic transition (TC ~ 280 K) in the field of 50 kOe, which can be attributed to the field-induced magnetic phase transition. The abnormalities of resistivity, Seebeck coefficient, normal Hall effect and thermal conductivity near TC are suggested to be associated with an abrupt reconstruction of electronic structure. Further, our results indicate an essential interaction among lattice, spin and charge degrees of freedom around TC. Such an interaction among various degrees of freedom associated with sudden phase transition is suggested to be characteristic of Mn-based antiperovskite compounds.

cond-mat.str-el↗
arXiv2009

Reversible room-temperature magnetocaloric effect with large temperature span in antiperovskite compounds Ga1-xCMn3+x (x=0, 0.06, 0.07, and 0.08)

The magnetic and magnetocaloric properties of Ga1-xCMn3+x have been investigated. Reversible magnetocaloric effect (MCE) occurs near the Curie temperature TC. The magnetic entropy change decreases with increasing x, though TC and magnetization increases. Meanwhile, the temperature span of vs. T plot becomes well broadened with x. Due to the competition between the broadening temperature span and decreasing, the relative cooling power (RCP) increases initially, and then decreases with increasing x. The largest RCP (2.1 J/cm3, under 45 kOe) observed when x=0.07 (TC = 296.5 K) is comparable to the contemporary magnetic refrigerant materials. Considering the reversible MCE, inexpensive and innoxious raw materials, our result suggests that Ga1-xCMn3+x can be promising candidate for magnetic refrigeration around room temperature.

cond-mat.str-el↗
arXiv2009

Large magnetic entropy change near room temperature in antipervoskite SnCMn3

We report the observation of large magnetocaloric effect near room temperature in antipervoskite SnCMn3. The maximal magnetic entropy change at the first-order ferrimagnetic-paramagnetic transition temperature (TC 279 K) is about 80.69mJ/cm3 K and 133mJ/cm3 K under the magnetic field of 20 kOe and 48 kOe, respectively. These values are close to those of typical magnetocaloric materials. The large magnetocaloric effect is associated with the sharp change of lattice, resistivity and magnetization in the vicinity of TC. Through the measurements of Seebeck coefficient and normal Hall effect, the title system is found to undergo a reconstruction of electronic structure at TC. Considering its low-cost and innocuous raw materials, Mn-based antiperovskite compounds are suggested to be appropriate for pursuing new materials with larger magnetocaloric effect.

cond-mat.str-el↗
arXiv2009

Anisotropic, Intermediate Coupling Superconductivity in Cu0.03TaS2

The anisotropic superconducting state properties in Cu0.03TaS2 have been investigated by magnetization, magnetoresistance, and specific heat measurements. It clearly shows that Cu0.03TaS2 undergoes a superconducting transition at TC = 4.03 K. The obtained superconducting parameters demonstrate that Cu0.03TaS2 is an anisotropic type-II superconductor. Combining specific heat jump = 1.6(4), gap ratio 2/kBTC = 4.0(9) and the estimated electron-phonon coupling constant ~ 0.68, the superconductivity in Cu0.03TaS2 is explained within the intermediate coupling BCS scenario. First-principles electronic structure calculations suggest that copper intercalation of 2H-TaS2 causes a considerable increase of the Fermi surface volume and the carrier density, which suppresses the CDW fluctuation and favors the raise of TC.

cond-mat.supr-con↗
arXiv2008

Single crystal growth and characterizations of Cu0.03TaS2 superconductors

Single crystal of Cu0.03TaS2 with low copper intercalated content was successfully grown via chemical iodine-vapor transport. The structural characterization results show that the copper intercalated 2H-Cu0.03TaS2 single crystal has the same structure of the CdI2-type structure as the parent 2H-TaS2 crystal. Electrical resistivity and magnetization measurements reveal that 2H-Cu0.03TaS2 becomes a superconductor below 4.2 K. Besides, electrical resistivity and Hall effects results show that a charge density wave transition occurs at TCDW = 50 K.

cond-mat.supr-con↗
arXiv2008

Crystal growth and superconductivity of FeSe_x

Single crystals FeSe_x have been grown in evacuated sealed quartz tube using a NaCl/KCl flux. The products include two crystal structures of tetragon and hexagon. The electronic transport and magnetic properties measurements of FeSe_x single crystal exhibits a superconducting transition at about 10K.

cond-mat.supr-con↗
arXiv2004

Structural, magnetic and transport properties in the Cu-doped manganites La0.85Te0.15Mn1-xCuxO3 (0 \leq x \leq 0.20)

The effect of Cu-doping at Mn-site on structural, magnetic and transport properties in electron-doped manganites La0.85Te0.15Mn1-xCuxO3 has been investigated. Based on the analysis of structural parameter variations, the valence state of the Cu ion in Cu-doped manganites is suggested to be +2. All samples undergo the paramagnetic-ferromagnetic (PM-FM) phase transition. The Curie temperature decreases and the transition becomes broader with increasing Cu-doping level, in contrast, the magnetization magnitude of Cu-doping samples at low temperatures increase as x \leq 0.15. The insulator-metal (I-M) transition moves to lower temperatures with increasing Cu-doping content and disappears as x > 0.1. In addition, the higher temperature resistivity r peak in double-peak-like r(T) curves observed in no Cu-doping sample is completely suppressed as Cu-doping level x = 0.1 and r(T) curve only shows single I-M transition at the low temperature well below . The results are discussed according to the change of magnetic exchange interaction caused by Cu-doping.

cond-mat.str-el↗
arXiv2004

Insulator-metal transition and the magnetic phase diagram of La1-xTexMnO3

The structural, electrical transport and magnetic properties of perovskite oxides La1-xTexMnO3 have been investigated and thus the magnetic phase diagram of La1-xTexMnO3 compounds as a function of temperature and the doping level x has been obtained. All samples have rhombohedral structure and undergo paramagnetic-ferromagnetic (PM-FM) transition accompanied with metal-insulator transition (MIT). Whereas a charge ordering (CO) transition begins to appear at for the sample with x=0.60. Moreover, the variation of the Curie temperature and the MIT temperature is quite complex and the results are discussed in terms of three factors including the average A-site cation radius , the size mismatch and the Te content. In addition, there has an evident magnetoresistance (MR) at low temperatures for all samples.

cond-mat.str-el↗
arXiv2004

The effect of oxygen stoichiometry on electrical transport and magnetic properties of La0.9Te0.1MnOy

The effect of the variation of oxygen content on structural, magnetic and transport properties in the electron-doped manganites La0.9Te0.1MnOy has been investigated. All samples show a rhombohedral structure with the space group . The Curie temperature decreases and the paramagnetic-ferromagnetic (PM-FM) transition becomes broader with the reduction of oxygen content. The resistivity of the annealed samples increases slightly with a small reduction of oxygen content. Further reduction in the oxygen content, the resistivity maximum increases by six orders of magnitude compared with that of the as-prepared sample, and the r(T) curves of samples with y = 2.86 and y = 2.83 display the semiconducting behavior () in both high-temperature PM phase and low-temperature FM phase, which is considered to be related to the appearance of superexchange ferromagnetism (SFM) and the localization of carriers. The results are discussed in terms of the combined effects of the increase in the Mn2+/(Mn2++Mn3+) ratio, the partial destruction of double exchange (DE) interaction, and the localization of carriers due to the introduction of oxygen vacancies in the Mn-O-Mn network.

cond-mat.str-el↗
arXiv2004

Structural, magnetic and transport properties in the Pr-doped manganites La0.9-xPrxTe0.1MnO3

The effect of Pr-doping on structural, magnetic and transport properties in electron-doped manganites La0.9-xPrxTe0.1MnO3 with fixed carrier concentration are investigated. The room temperature structural transition from rhombohedral (R3C) to orthorhombic (Pbnm) symmetry is found in the samples with by the Rietveld refinement of x-ray powder diffraction patterns. The Curie temperature of samples decreases and the transition becomes broader with increasing Pr-doping level. For the samples with, there exist insulator-metal (I-M) transition. And the low-temperature I-M transition is observed at about 66K for the sample with x = 0.36, which may be related to the opening of a new percolation channel. For the samples with, r(T) curves display the semiconducting behavior (dρ/dT < 0) in both high-temperature PM phase and low-temperature FM phase. The results are discussed in terms of the increased bending of the Mn-O-Mn bond with decreasing the average ionic radius of the A-site element and the tolerance factor, resulting in the narrowing of the bandwidth, the decrease of the mobility of electrons and the weakening of DE interaction caused by the substitution of smaller Pr3+ ions for larger La3+ ion.

cond-mat.str-el↗