| 1. |
- Anil Kumar, Puri, et al.
(författare)
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Magnetic polarons and spin-glass behavior in insulating La1-xSrxCoO3 (x = 0.125 and 0.15)
- 2020
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Ingår i: Physical Review Research. - : AMER PHYSICAL SOC. - 2643-1564. ; 2:4
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Tidskriftsartikel (refereegranskat)abstract
- The evolution of magnetic polarons in Sr doped LaCoO3 (La1-xSrxCoO3) single crystal and polycrystalline samples are investigated by employing dc and ac magnetic measurement and small angle neutron scattering (SANS) techniques. The effect of magnetic field and temperature on magnetic polarons is experimentally studied for La0.875Sr0.125CoO3 and La0.85Sr0.15CoO3 compounds that belong to the spin glass insulating regime of the broader compositional phase diagram of this system. Langevin analyses of the isothermal magnetization curves in the notional paramagnetic regime prove the existence of magnetic polarons with large moments. The dc field superimposed ac susceptibility data and the analysis of the glassy dynamics prove that the size of polarons in 15% Sr doped crystal increase as the field is increased while the field effect is not visible in the 12.5% Sr doped crystal. A polycrystalline sample of La0.85Sr0.15CoO3 is analyzed by SANS experiments, which confirm nonzero correlation length at temperatures far above the macroscopic ordering temperature and hence the presence of magnetic polarons.
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| 2. |
- Dan, Tinku, et al.
(författare)
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Local structural evolution in the anionic solid solution ZnSexS1-x
- 2021
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Ingår i: Physical Review B. - : American Physical Society. - 2469-9950 .- 2469-9969. ; 104:18
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Tidskriftsartikel (refereegranskat)abstract
- The century-old Vegard's law has been remarkably accurate in describing the evolution of the lattice parameters of almost all solid solutions. Contractions or expansions of lattice parameters of such systems depend on the size of the guest atom being smaller or larger than the host atom it replaces to form the solid solution. This has given rise to the concept of "chemical pressure" in analogy to the physical pressure. We have investigated using EXAFS the evolution of the local structure in terms of atom-pair distances extending up to the third-nearest neighbors in the family of compounds, ZnSexS1-x as an example of an anionic solid solution, in contrast to all previous studies focusing on cationic solid solutions. Our results establish several common features between these two types of solid solutions, while strongly suggesting that the concept of a chemical pressure is inaccurate and misleading. Most interestingly, we also find a qualitative difference between the cationic solid solutions, reported earlier, and the anionic solid solution.
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| 3. |
- Esteban-Puyuelo, Raquel, et al.
(författare)
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Complexity of mixed allotropes of MoS2 unraveled by first-principles theory
- 2020
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Ingår i: Physical Review B. - : AMER PHYSICAL SOC. - 2469-9950 .- 2469-9969. ; 102:16
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Tidskriftsartikel (refereegranskat)abstract
- Two-dimensional MoS2 forms stable and several metastable allotropes of semimetallic, metallic, and semiconducting characters, depending on the experimental growth conditions. In this paper we consider intergrowth of the two most frequently reported metastable phases of MoS2 (1T and 1T') within the stable 1H phase to establish the effect of geometric and electronic reconstructions of the interface region between 1H and T/1T' phases using first-principles density functional calculations. We show that a complex structural reconstruction at the interfaces is responsible for the opening of an energy gap driving the electronic and geometric structures to resemble that of the 1T' phase. It is also found that the size of the patches inside the 1H matrix crucially controls the geometry and electronic structure close to the Fermi level. These results establish that remarkable properties of chemically exfoliated MoS2 with patches of metastable structures are to be understood as arising fundamentally from intergrowths necessarily strained due to lattice mismatch across the interface between the H and the distorted T phase, rather than in terms of any pure metastable phase.
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| 4. |
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| 5. |
- Kundu, S., et al.
(författare)
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Signatures of a Spin-1/2 Cooperative Paramagnet in the Diluted Triangular Lattice of Y2CuTiO6
- 2020
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Ingår i: Physical Review Letters. - : AMER PHYSICAL SOC. - 0031-9007 .- 1079-7114. ; 125:11
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Tidskriftsartikel (refereegranskat)abstract
- We present a combination of thermodynamic and dynamic experimental signatures of a disorder driven dynamic cooperative paramagnet in a 50% site diluted triangular lattice spin-1/2 system: Y2CuTiO6. Magnetic ordering and spin freezing are absent down to 50 mK, far below the Curie-Weiss scale (-theta(CW)) of similar to 134 K. We observe scaling collapses of the magnetic field and temperature dependent magnetic heat capacity and magnetization data, respectively, in conformity with expectations from the random singlet physics. Our experiments establish the suppression of any freezing scale, if at all present, by more than 3 orders of magnitude, opening a plethora of interesting possibilities such as disorder stabilized long range quantum entangled ground states.
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| 6. |
- Sarkar, S., et al.
(författare)
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Structural and electronic properties of the random alloy ZnSexS1-x
- 2022
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Ingår i: Physical Review B. - : American Physical Society. - 2469-9950 .- 2469-9969. ; 105:18
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Tidskriftsartikel (refereegranskat)abstract
- In this article we employ density functional theory in the generalized gradient approximation to investigate the structural and electronic properties of the solid solution alloy ZnSexS1-x in the wurtzite structure. We analyzed the character of the bond lengths and angles at the atomic scale, using a supercell approach that does not impose any constraint on the crystal potential. We show that the bond lengths of pristine ZnS and ZnSe compounds are almost preserved between nearest neighbors, which is different from what would be anticipated if Vegard's law were valid at the atomic level. We also show that bond lengths start behaving in accordance with Vegard's law from the third shell of nearest neighbors onward, which in turn determines the average lattice parameters of the alloys determined by diffraction experiments. Fundamental building blocks around the anions are identified and are shown to be nonrigid but still volume preserving. Finally, the geometrical analysis is connected to the trend exhibited by the electronic structure, and in particular by the band gap. The latter is found to exhibit a small deviation from linearity with respect to the Se concentration, in accordance with available experimental data. By assuming a quadratic dependence, we can extract a bowing parameter and analyze various contributions to it with various calculations under selected constraints. The structural deformation in response to the doping process is shown to be the driving force behind the deviation from linearity. The difference in stiffness between ZnS and ZnSe is shown to play a key role in the asymmetric behavior of the bowing parameter observed in the S-rich and Se-rich regions.
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