Browsing by Author "Mollah, S"

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Electronic and magnetic instability in Pr0.65Ca0.25Sr0.1MnO3
(2003-09-01)
Mollah, S
;
Huang, HL
;
Liu, SJ
;
Ho, PL
;
Huang, WL
Electronic and magnetic instability in polycrystalline Pr0.65Ca0.25Sr0.1MnO3 manganite has been established from a systematic study of resistivity (p), magnetization (M) and specific heat (C). The sample shows a charge ordering transition at T-CO similar to 200 K, an antiferromagnetic (AFM) ordering transition at T-N similar to 175 K, a metal-insulator (MI) transition at T-MI similar to 80 K and an unusual magnetic ordering transition at T-M(*) similar to 45 K in the absence of magnetic fields. Though the C data do not show any anomaly at T-MI for MI transition, these illustrate a much smaller anomaly than expected one at T-M* and is suppressed by magnetic fields. This indicates that the unusual magnetic ordering in this sample is of canted, fluctuated or phase separation of AFM and ferromagnetic in nature which is established from the T-H phase diagram, as well as the thermal and magnetic hysteresis in p, M and C. (C) 2003 Elsevier Science B.V. All rights reserved.
Magnetic field dependence of low-temperature specific heat of the spinel oxide superconductor LiTi2O4
(2004-08-01)
Sun, CP
;
Lin, JY
;
Mollah, S
;
Ho, PL
;
Yang, HD
Magnetic field dependence of low temperature specific heat of spinel oxide superconductor LiTi2O4 has been elaborately investigated. In the normal state, the obtained electronic coefficient of specific heat gamma(n)=19.15 mJ/mol K-2, the Debye temperature Theta(D)=657 K and some other parameters are compared with those reported earlier. The superconducting transition at T(c)similar to11.4 K is very sharp (DeltaT(c)similar to0.3 K) and the estimated deltaC/gamma(n)T(c) is similar to1.78. In the superconducting state, the best fit of data leads to the electronic specific heat C-es/gamma(n)T(c)=9.87 exp(-1.58 T-c/T) without field and gamma(H)proportional toH(0.95) with fields. In addition, H-c2(0)similar to11.7 T, H-c(0)similar to0.32 T, xi(GL)(0)similar to55 A, lambda(GL)(0)similar to1600 Angstrom, and H-c1(0)similar to26 mT are estimated from the Werthamer-Helfand-Hohenberg (WHH) theory or other relevant relations. All results from the present study indicate that LiTi2O4 can be well described by a typical type-II, BCS-like, moderate coupling, and fully gapped superconductor in the dirty limit. It is further suggested that LiTi2O4 is a moderately electron-electron correlated system.
Pressure effects on the transition temperature of superconducting MgCxNi3
(2003-09-01)
Yang, HD
;
Mollah, S
;
Huang, WL
;
Ho, PL
;
Huang, HL
The effect of hydrostatic pressure (P) up to 17 kbar on the superconducting transition temperature (T-C) of the newly discovered intermetallic nonoxide perovskite superconductor MgCxNi3 has been reported. T-C is found to increase with increasing P at a rate of dT(C)/dPsimilar to0.0134 to 0.0155 K/kbar depending on the value of carbon content x. The absolute value of dT(C)/dP for MgCxNi3 is about the same as that of intermetallic RNi2B2C (R denotes rare earth) and metallic superconductors but about one order of magnitude smaller than that of the most recently and intensively studied superconductor MgB2. However, the d ln T-C/dPsimilar to0.001 81 to 0.002 24 kbar(-1) and the rate of change of T-C with unit cell volume (V), d ln T-C/d ln Vsimilar to-3.18 to -2.58 of MgCxNi3 are having the comparable magnitude to that of MgB2 with opposite sign. The increase of T-C with P in MgCxNi3 can be explained in the framework of density of states (DOS) effect.