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ABSTRACT: Structure induced conductivity enhancement in metal-doped molybdenum oxide thin films J. Appl. Phys. 113, 043109 (2013) Structural variants and the modified Slater-Pauling curve for transition-metal-based half-Heusler alloys We investigate the structural, magnetic, and electrical properties of charge-spin co-doped Ba 1ÀxÀy La xþy Ti 1Àx M x O 3 (M ¼ Cr, Fe, and Co). For Ba 1ÀxÀy La xþy Ti 1Àx Cr x O 3 , carrier doping induces short-range ferromagnetism, and we find a large negative magnetoresistance in these compounds. However, for Ba 1ÀxÀy La xþy Ti 1Àx M x O 3 (M ¼ Fe and Co), the magnetism does not seem to couple with the charge carriers. The transport properties of Ba 1ÀxÀy La xþy Ti 1Àx Cr x O 3 can be described by a three-dimensional variable-range-hopping model that implies itinerant charge carriers, whereas almost all the samples of Ba 1ÀxÀy La xþy Ti 1Àx M x O 3 (M ¼ Fe and Co) exhibit high resistivity. It is known that only the itinerant charge carriers can enhance the coupling of two isolated magnetic ions. Therefore, there is almost no long-range ferromagnetism in the studied system. V C 2013 American Institute of Physics. [http://dx.doi.org/10.1063/1.4790869]
Journal of Applied Physics 02/2013; 113(6):063902. · 2.17 Impact Factor
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ABSTRACT: Recently, we successfully synthesized the nitrogen-deficient manganese antiperovskites AlNxMn3 with the very high ferromagnetic Curie temperatures TC up to 818 K [Lin et al., Appl. Phys. Lett. 98, 092507 (2011)]. In order to figure out the role of nitrogen for the magnetism, in the present work, we performed a theoretical investigation on AlNxMn3 through the first-principles calculation based on density functional theory. The results show that AlNxMn3 have the ferromagnetic ground states, and the total magnetic moments in a cell are enhanced with decreasing the nitrogen concentration. Based on the calculations of band structure and density of states, we showed the influence of nitrogen concentration on magnetism for AlNxMn3: The decreasing of nitrogen concentration from ideal AlNMn3 moves the spin-down bands towards the high energy remarkably, which enhances the exchange splitting energy ΔEex; on the other hand, nitrogen deficiency reduces the Mn-N hybridizations, which makes the 3d electrons of Mn tend to occupy the spin-up states. The nitrogen deficiency reduces the Mn-N hybridization, which narrows Mn-d bands and enhances the spin polarization. Furthermore, we estimated TC of AlNxMn3, and found the calculated TC can be scaled by spin fluctuation temperature TSF, suggesting AlNxMn3 belong to the spin fluctuation system.
Journal of Applied Physics 01/2013; 113(2):23905. · 2.17 Impact Factor
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Y. M. Xie,
Z. R. Yang,
L. Li,
L. H. Yin,
X. B. Hu,
Y. L. Huang,
H. B. Jian,
W. H. Song, Y. P. Sun,
S. Q. Zhou,
Y. H. Zhang
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ABSTRACT: The correlation between colossal magnetocapacitance (CMC) and colossal
magnetoresistance (CMR) in CdCr2S4 system has been revealed. The CMC is induced
in polycrystalline Cd0.97In0.03Cr2S4 by annealing in cadmium vapor. At the same
time, an insulator-metal transition and a concomitant CMR are observed near the
Curie temperature. In contrast, after the same annealing treatment, CdCr2S4
displays a typical semiconductor behavior and does not show magnetic field
dependent dielectric and electric transport properties. The simultaneous
occurrence or absence of CMC and CMR effects implies that the CMC in the
annealed Cd0.97In0.03Cr2S4 could be explained qualitatively by a combination of
CMR and Maxwell-Wagner effect.
12/2012;
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ABSTRACT: The surface magnetic behavior of La(0.8)Ca(0.2)MnO(3) nanoparticles was investigated. We observed irreversibility in high magnetic field. The surface spin-glass behavior as well as the high-field irreversibility is suppressed by increasing particle size while the freezing temperature T(F) does not change with particle size. The enhanced coercivity has been observed in the particles and we attributed it to the large surface anisotropy. We have disclosed a clear relationship between the particle size, the thickness of the shell, and the saturation magnetization of the particles. The large reduction of the saturation magnetization of the samples is found to be induced by the increase of nonmagnetic surface large since the thickness of the spin-disordered surface layer increases with a decrease in the particle size. Due to the reduction of the magnetization, the magnetocaloric effect (MCE) has been reduced by the decreased particle size since the nonmagnetic surface contributes little to the MCE. Based on the core-shell structure, large relative cooling powers RCP(s) of 180 J/kg and 471 J/kg were predicted for a field change of 2.0 T and 4.5 T, respectively, in the small particles with thin spin-glass layer.
Journal of Applied Physics 12/2012; 112(12):123903. · 2.17 Impact Factor
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Y M Xie,
Z R Yang,
L Li,
L H Yin,
X B Hu,
Y L Huang,
H B Jian,
W H Song, Y P Sun,
S Q Zhou,
Y H Zhang
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ABSTRACT: The correlation between colossal magnetocapacitance (CMC) and colossal magnetoresistance (CMR) in CdCr 2 S 4 system has been revealed. The CMC is induced in polycrystalline Cd 0.97 In 0.03 Cr 2 S 4 by annealing in cadmium vapor. At the same time, an insulator-metal transition and a concomitant CMR are observed near the Curie temperature. In contrast, after the same annealing treatment, CdCr 2 S 4 displays a typical semiconductor behavior and does not show magnetic field dependent dielectric and electric transport properties. The simultaneous occurrence or absence of CMC and CMR effects implies that the CMC in the annealed Cd 0.97 In 0.03 Cr 2 S 4 could be explained qualitatively by a combination of CMR and Maxwell-Wagner effect. a) Corresponding author.
Journal of Applied Physics 12/2012; 112(24):123912. · 2.17 Impact Factor
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ABSTRACT: We theoretically designed and investigated the layered antiperovskite nickel carbides A2CNi4 with different A-site elements by using the first-principles calculation based on density functional theory (DFT). The calculated formation energies for a series of A-site elements show that Al2CNi4, Ga2CNi4, and Sn2CNi4 are stable and can be synthesized at ambient pressure. The elastic properties and electronic band structures were calculated and discussed. Similar to the superconducting MgCNi3, the three stable compounds show the non-magnetic ground states. The density of states at Fermi level N(EF), dominated by Ni-3d electrons, can be comparable with the N(EF) of MgCNi3. The electron and hole bands cross the Fermi level, indicating the multiple-band nature for A2CNi4 (A = Al, Ga, and Sn). Using the McMillan's formula, we approximately estimated the superconducting parameters such as electron-phonon coupling constants λ and superconducting transition temperatures TC. Our present results show that the layered antiperovskite nickel carbides A2CNi4 (A = Al, Ga, and Sn) may be potential weak-coupling superconductors with TC about 5∼7 K.
AIP Advances. 11/2012; 2(4):042167.
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ABSTRACT: We have performed high-resolution angle-resolved photoemission spectroscopy of layered chalcogenide 1T-Fe_{x}Ta_{1-x}S_{2} which undergoes a superconducting transition in the nearly commensurate charge-density-wave phase (melted Mott phase). We found a single electron pocket at the Brillouin-zone center in the melted Mott phase, which is created by the backfolding of bands due to the superlattice potential of charge-density-wave. This electron pocket appears in the x region where the samples show superconductivity, and is destroyed by the Mott- and Anderson-gap opening. Present results suggest that the melted Mott state and the superconductivity coexist in real space, providing a new insight into the interplay between electron correlation, charge order, and superconductivity.
Physical Review Letters 10/2012; 109(17):176403. · 7.37 Impact Factor
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ABSTRACT: The structural and magnetic properties of Bi6Fe2Ti3O18 and Bi6FeCrTi3O18 are investigated. The samples can be indexed by an orthorhombic lattice with the space group B2cb and the valence state of Fe and Cr ions is suggested to be +3 based on the x-ray photoelectron spectroscopy spectra. The sample Bi6Fe2Ti3O18 is paramagnetic with the presence of a short-range antiferromagnetic ordering; whereas Bi6FeCrTi3O18 undergoes a short-range ferrimagnetic-like transition at 106 K originating from the spin canting of the antiferromagnetic coupling of Fe-based and Cr-based sublattices via the Dzyaloshinskii-Moriya interaction due to the distorted crystal structure of Bi6FeCrTi3O18, which are in agreement with the EPR results. The magnetic structure and EPR spectra of Bi6Fe2Ti3O18 and Bi6FeCrTi3O18 can be understood by the presence of a small amount of isolated Fe3+ ions in an octahedral ligand field with a low symmetry and the coupling between the random occupancy of Fe3+ and/or Cr3+ ions in other two octahedral sites in the layered structure of Aurivilius phase.
Phys. Rev. B. 09/2012; 86(10).
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ABSTRACT: We report X-ray diffraction, magnetization and transport measurements for
polycrystalline samples of the new layered superconductor Bi4-xAgxO4S3
(0<x<0.2). The superconducting transition temperature (TC) decreases gradually
and finally suppressed for x>0.10. Accordingly, the resistivity changes from a
metallic behavior for x<0.1 to a semiconductor-like behavior for x>0.1. The
analysis of Seebeck coefficient shows there are two types of electron-like
carriers dominate at different temperature regions, indicative of a multiband
effect responsible for the transport properties. The suppression of
superconductivity and the increased resistivity can be attributed to a shift of
the Fermi level to the lower-energy side upon doping, which reduces the density
of states at EF. Further, our result indicates the superconductivity in the
parent Bi4O4S3 is intrinsic and the dopant Ag prefers to enter the BiS2 layers,
which may essentially modify the electronic structure.
08/2012;
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ABSTRACT: Polycrystalline sample of the new layered superconductor Bi4O4S3 is
successfully synthesized by solid-state reaction method by using Bi, S and
Bi2O3 powders with one step reaction. The superconducting transition
temperature (Tconset=4.5 K), the zero resistance transition temperature
(Tc0=4.07 K) and the diamagnetic transition temperature (4.02 K at H=10 Oe)
were confirmed by electrical transport and magnetic measurements. Also, our
results indicate a typical type II-superconductor behavior. In addition, a
large thermoelectric effect was observed with a dimensionless thermoelectric
figure of merit (ZT) of about 0.03 at 300K, indicating Bi4O4S3 can be a
potential thermoelectric material.
07/2012;
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ABSTRACT: The structural and magnetic properties of Ba0.8La0.2Ti1−xCoxO3 (0 x 0.2) have been investigated. All samples show a cubic structure with the space group of P m3m at room temperature. Ba0.8La0.2TiO3 exhibits a carrier induced Pauli-paramagnetism and Ba0.8La0.2Ti0.9Co0.1O3 shows a Curie-Weiss like paramagnetism. With increasing cobalt doping, Ba0.8La0.2Ti0.8Co0.2O3 seems to undergo a spin glass like transition at T f = 10.1 K as evidenced by the frequency dependence of ac susceptibility measure-ments, aging effect measurements, memory effect measurements and magnetic relaxation measurements. The time decay of the thermoremnant magnetization can be well described with the stretched exponential function. It is worthwhile to note that the temperature dependence of relaxation characteristic time τr and the critical exponent n deduced from the function show opposite tendencies below and above T f , and the possible reason has been discussed. n at T f close to 2/3 suggests that Ba0.8La0.2Ti0.8Co0.2O3 may be a three dimensional Ising spin glass.
The European Physical Journal B. 05/2012; 85:156.
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ABSTRACT: Single-phase delafossite CuAlO2 thin films are deposited successfully on Al2O3 (001) and YSZ (100) substrates using the chemical solution method. X-ray diffraction data present that the CuAlO2 film on the Al2O3 (001) substrate is epitaxial, whereas that on YSZ (100) is c-axis oriented; the same is also demonstrated by the HRTEM images and SAED patterns. Optical transmittance spectra exhibit
that both films have high transparency in the visible region. However, in this region, the optical transmittance of the CuAlO2 thin film deposited on (001) Al2O3 is inferior to that deposited on (100) YSZ. This optical anomaly can be attributed to surface scattering. Electrical transport
measurements show that the resistivity of the film on (001) Al2O3 is one order lower than that on (100) YSZ, suggesting that in-plane orientation is significant in improving hole mobility.
KeywordsCuAlO2
–Delafossite–Al2O3
–YSZ–Optical property–Electrical property–Chemical solution method
Journal of Sol-Gel Science and Technology 05/2012; 58(1):12-17. · 1.63 Impact Factor
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ABSTRACT: The intrinsically core/shell structured La0.6Sr0.4MnO3 nanoparticles with amorphous shells and ferromagnetic cores have been prepared. The magnetic, dielectric and microwave absorption
properties are investigated in the frequency range from 1 to 12GHz. An optimal reflection loss of −41.1dB is reached at
8.2GHz with a matching thickness of 2.2mm, the bandwidth with a reflection loss less than −10dB is obtained in the 5.5–11.3GHz
range for absorber thicknesses of 1.5–2.5mm. The excellent microwave absorption properties are a consequence of the better
electromagnetic matching due to the existence of the protective amorphous shells, the ferromagnetic cores, as well as the
particular core/shell microstructure. As a result, the La0.6Sr0.4MnO3 nanoparticles with amorphous shells and ferromagnetic cores may become attractive candidates for the new types of electromagnetic
wave absorption materials.
Nanoscale Research Letters 04/2012; 4(10):1153-1158. · 2.73 Impact Factor
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ABSTRACT: In this paper, the pressure effect on superconductivity and magnetism has been investigated in FeSe
x
(x=0.80,0.88). The magnetization curves display anomaly at T
s1∼106K and T
s2∼78K except for the superconducting diamagnetic transition around T
c
∼8K. The magnetic anomaly at T
s1 and T
s2 can be related to a ferromagnetic and an antiferromagnetic phase transition, respectively, as revealed by specific heat measurements.
The application of pressure not only raises T
c
, but also increases both T
s1 andT
s2.
Journal of Superconductivity and Novel Magnetism 04/2012; 22(7):667-670. · 0.65 Impact Factor
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ABSTRACT: The effects of carbon concentration on the crystal structure, magnetic, and electrical/thermal transport properties of ZnCxFe3 (1.0 ≤ x ≤ 1.5) have been investigated systematically. Both the Curie temperature and the saturated magnetization decrease firstly and then reach saturation with increasing x. The investigations of heat capacity and resistivity indicate that ZnC1.2Fe3 displays a strongly correlated Fermi liquid behavior considering its Kadowaki-Woods ratio (∼0.64 a0). Around the ferromagnetic-paramagnetic phase transition (∼358 K), a reversible room-temperature magnetocaloric effect is observed. The relative cooling power (RCP) is ∼164 J/kg (∼385 J/kg) with the magnetic field change ΔH = 20 kOe (45 kOe). Considering the considerable large RCP, inexpensive and innoxious raw materials, ZnC1.2Fe3 is suggested to be a promising candidate for room-temperature magnetic refrigeration. Furthermore, the studies of thermal transport properties indicate that ZnC1.2Fe3 can also be a potential thermoelectric material with the dimensionless figure of merit (ZT = α2T/ρk) reaching its maximum of 0.0112 around 170 K.
Journal of Applied Physics 10/2011; 110(8):083914-083914-8. · 2.17 Impact Factor
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ABSTRACT: We report the interplay between charge-density-wave (CDW) and
superconductivity of 1$T$-Fe$_{x}$Ta$_{1-x}$S$_{2}$ ($0\leq x \leq 0.05$)
single crystals. The CDW order is gradually suppressed by Fe-doping,
accompanied by the disappearance of pseudogap/Mott-gap as shown by the density
functional theory (DFT) calculations. The superconducting state develops at low
temperatures within the CDW state for the samples with the moderate doping
levels. The superconductivity strongly depends on $x$ within a narrow range,
and the maximum superconducting transition temperature is 2.8 K as $x=0.02$. We
propose that the induced superconductivity and CDW phases are separated in real
space. For high doping level ($x>0.04$), the Anderson localization (AL) state
appears, resulting in a large increase of resistivity. We present a complete
electronic phase diagram of 1$T$-Fe$_{x}$Ta$_{1-x}$S$_{2}$ system that shows a
dome-like $T_{c}(x)$.
09/2011;
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ABSTRACT: W-type barium hexaferrite platelets Ba(ZnxCo1−x)2Fe16O27 (0.1 ≤ x ≤ 0.9) were prepared by a chemical coprecipitation route. The results of field-emission scanning electronic microscopy showed that the grains were regular hexagonal platelets with sizes from 0.5 to 1.5 μm. With increasing x, the coercivity decreased, whereas the saturation magnetization increased. Microwave absorption properties were investigated in the frequency range of 8–12 GHz. An optimal reflection loss (−24.8 dB) reached at 10 GHz for x = 0.5 with a thickness of 2 mm. These results indicated that our samples might be a potential candidate for permanent magnets and microwave absorption materials.
Journal of Applied Physics 04/2011; 109(7):07E536-07E536-3. · 2.17 Impact Factor
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ABSTRACT: High quality FeSe thin films with different ratios of Fe to Se have been grown on GaAs and Si substrates by changing the flow rate of Fe(CO)5 in a low-pressure metal–organic chemical vapor deposition (MOCVD) system. For both substrates, the films grown at a low flow rate of Fe(CO)5 are non-ferromagnetic and exhibit superconductivity at low temperature, while those grown at a high flow rate of Fe(CO)5 display ferromagnetic and semiconducting behaviors. Our results suggest that the superconducting phase does exist in a narrow range of Fe and Se concentration near stoichiometry. The introduction of excess Fe favors ferromagnetism and leads to the suppression of superconductivity.
Superconductor Science and Technology 12/2010; 24(1):015010. · 2.66 Impact Factor
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ABSTRACT: The magnetization and anisotropic electrical transport properties have been measured in high quality Cu(0.03)TaS(2) single crystals. A pronounced peak effect has been observed, indicating that high quality and homogeneity are vital to the peak effect. A kink has been observed in the magnetic field, H, dependence of the in-plane resistivity ρ(ab) for H is parallel to c, which corresponds to a transition from activated to diffusive behavior of the vortex liquid phase. In the diffusive regime of the vortex liquid phase, the in-plane resistivity ρ(ab) is proportional to H(0.3), which does not follow the Bardeen-Stephen law for free flux flow. Finally, a simplified vortex phase diagram of Cu(0.03)TaS(2) for H is parallel to c is given.
Journal of Physics Condensed Matter 12/2010; 22(50):505704. · 2.55 Impact Factor
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ABSTRACT: We report the structural, magnetic, electrical transport properties, and magnetocaloric effect (MCE) of antipervoskite compound AlCMn3. It exhibits a second-order ferromagnetic–paramagnetic phase transition around (TC) 287 K. The electronic resistivity (ρ) shows a good metallic behavior except for a slope change around TC. At lower temperatures (below 130 K), ρ∝T2 indicates that the electron-electron scatterings domain. At evaluated temperatures (130–270 K), ρ is linear dependence on temperature, implying that the phonon scatterings boost up greatly. Furthermore, a broad distribution of the magnetic entropy change (−ΔSM) peak is found to about 100 K with the magnetic field change ΔH = 45 kOe. The relative cooling power are ∼ 137 J/kg and ∼ 328 J/kg (or ∼ 68 K2 and ∼ 162 K2) with ΔH = 20 kOe and 45 kOe, respectively. All these values are comparable with the typical MCE associated with a second-order transition. It suggests that AlCMn3 may be considered as a candidate material for near room-temperature magnetic refrigeration because of: (i) the large full width at half peak of the −ΔSM-T curve, (ii) no hysteresis losses, (iii) the near room-temperature working temperature, and (iv) the low-cost and innoxious raw materials. Moreover, it is found that the simple theoretical model which only considering the magnetoelastic and magnetoelectronic couplings couldn’t account well for the observed MCE in antiperovskite AlCMn3.
Journal of Applied Physics. 11/2010; 108(9):093925-093925-6.
