| 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. |
- Jana, Somnath, et al.
(författare)
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Atomic-scale chemical fluctuation in LaSrVMoO6, a proposed half-metallic antiferromagnet
- 2010
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Ingår i: Physical Review B. Condensed Matter and Materials Physics. - 1098-0121 .- 1550-235X. ; 82:18
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Tidskriftsartikel (refereegranskat)abstract
- Half-metallic antiferromagnets (HMAFMs) have been proposed theoretically long ago but have not been realized experimentally yet. Recently, a double perovskite compound, LaSrVMoO6, has been claimed to be an almost real HMAFM system. Here, we report detailed experimental and theoretical studies on this compound. Our results reveal that the compound is neither a half-metal nor an ordered antiferromagnet. Most importantly, an unusual chemical fluctuation is observed locally, which finally accounts for all the electronic and magnetic properties of this compound.
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| 3. |
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| 4. |
- Jana, Somnath, et al.
(författare)
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LaSrVMoO6 : A case study for A-site covalency-driven local cationic order in double perovskites
- 2012
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Ingår i: Physical Review B. Condensed Matter and Materials Physics. - 1098-0121 .- 1550-235X. ; 86:1
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Tidskriftsartikel (refereegranskat)abstract
- An unusual atomic scale chemical fluctuation in LaSrVMoO6, in terms of narrow patches of La, V and Sr,Mo-rich phases, has been probed in detail to understand the origin of such a chemical state. Exhaustive tuning of the equilibrium synthesis parameters showed that the extent of phase separation can never be melted down below a unit cell dimension making it impossible to achieve the conventional B-site ordered structure, which establishes that the observed "inhomogeneous" patchlike structure with minimum dimension of few angstroms is a reality in LaSrVMoO6. Therefore another type of local chemical order, hitherto unknown in double perovskites, gets introduced here. X-ray diffraction, electron microscopy elemental mapping, magnetic, and various spectroscopic studies have been carried out on samples, synthesized under different conditions. These experimental results in conjunction with ab initio electronic structure calculation revealed that it is the energy stability, gained by typical La-O covalency as in LaVO3, that leads to the preferential La, V and Sr,Mo ionic proximity, and the consequent patchy structure.
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| 5. |
- Jana, Somnath, et al.
(författare)
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Revisiting Goodenough-Kanamori rules in a new series of double perovskites LaSr1-xCaxNiReO6
- 2019
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Ingår i: Scientific Reports. - : Springer Science and Business Media LLC. - 2045-2322 .- 2045-2322. ; 9:1
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Tidskriftsartikel (refereegranskat)abstract
- The magnetic ground states in highly ordered double perovskites LaSr1-xCaxNiReO6 (x = 0.0, 0.5, 1.0) are studied in view of the Goodenough-Kanamori rules of superexchange interactions in this paper. In LaSrNiReO6, Ni and Re sublattices are found to exhibit curious magnetic states separately, but no long range magnetic ordering is achieved. The magnetic transition at similar to 255 K is identified with the independent Re sublattice magnetic ordering. Interestingly, the sublattice interactions are tuned by modifying the Ni-O-Re bond angles through Ca doping. Upon Ca doping, the Ni and Re sublattices start to display a ferrimagnetically ordered state at low temperature. The neutron powder diffraction data reveals long range ferrimagnetic ordering of the Ni and Re magnetic sublattices along the crystallographic b-axis. The transition temperature of the ferrimagnetic phase increases monotonically with increasing Ca concentration.
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| 6. |
- Jana, Somnath, et al.
(författare)
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Signature of an antiferromagnetic metallic ground state in heavily electron-doped Sr2FeMoO6
- 2012
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Ingår i: Physical Review B. Condensed Matter and Materials Physics. - 1098-0121 .- 1550-235X. ; 86:5, s. 054433-
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Tidskriftsartikel (refereegranskat)abstract
- Sr2FeMoO6 is a well-known double perovskite with exciting high-temperature magnetic properties. Through various magnetic and spectroscopic measurements, we collect compelling evidence here that this compound can be driven into a rare three-dimensional antiferromagnetic metallic state by heavy electron doping (70% Sr2+ substitution by La3+). Moreover, local structural study of these Sr2-xLaxFeMoO6 (1.0 <= x <= 1.5) compounds reveals unusual atomic scale phase distribution in terms of La,Fe- and Sr,Mo-rich regions driven by strong La-O covalency, a phenomenon hitherto undisclosed in double perovskites. The general trend of our findings is in agreement with theoretical calculations carried out on realistic structures having local chemical fluctuations, which reconfirms the relevance of the kinetic-energy-driven magnetic model.
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| 7. |
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| 8. |
- Kumar, P. Anil, et al.
(författare)
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Magnetoresistance and electroresistance effects in Fe3O4 nanoparticle system
- 2014
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Ingår i: Journal of experimental nanoscience. - : Informa UK Limited. - 1745-8080 .- 1745-8099. ; 9:4, s. 391-397
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Tidskriftsartikel (refereegranskat)abstract
- Nearly monodisperse spherical magnetite (Fe3O4) nanoparticles are prepared by colloidal chemistry route. Magnetic and electronic transport properties of the annealed pellets of these nanoparticles are reported. Effect of external magnetic and electric fields on the magnetic and transport properties of the material are studied as a function of temperature. We find that the highest resistance state of the ferromagnetic system occurs at a magnetic field which is approximately equal to its magnetic coercivity; this establishes the magnetoresistance (MR) in this system to be of the conventional tunnelling type MR as against the spin-valve type MR found more recently in some ferromagnetic oxide systems. The material also shows electroresistance (ER) property with its low-temperature resistance being strongly dependent on the excitation current that is used for the measurement. This ER effect is concluded to be intrinsic to the material and is attributed to the electric field-induced melting of the charge-order state in magnetite.
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| 9. |
- Kumar Puri, Anil, et al.
(författare)
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Reentrant Superspin Glass Phase in a La0.82Ca0.18MnO3 Ferromagnetic Insulator
- 2014
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Ingår i: Physical Review X. - 2160-3308. ; 4:1, s. 011037-
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Tidskriftsartikel (refereegranskat)abstract
- We report results of the magnetization and ac susceptibility measurements down to very low fields on a single crystal of the perovskite manganite, La-0.82 Ca-0.18 MnO3. This composition falls in the intriguing ferromagnetic insulator region of the manganite phase diagram. In contrast to earlier beliefs, our investigations reveal that magnetically (and in every other sense), this is a single- phase system with a ferromagnetic ordering temperature of around 170 K. However, this ferromagnetic state is magnetically frustrated, and the system exhibits pronounced glassy dynamics below 90 K. Based on measured dynamical properties, we propose that this quasi-long-ranged ferromagnetic phase, and the associated superspin glass behavior, is the true magnetic state of the system, rather than being a macroscopic mixture of ferromagnetic and antiferromagnetic phases, as often suggested. Our results provide an understanding of the quantum phase transition from an antiferromagnetic insulator to a ferromagnetic metal via this ferromagnetic state as a function of x in La1-xCaxMnO3, in terms of the possible formation of magnetic polarons.
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| 10. |
- Kuschel, Maxwell, et al.
(författare)
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Investigating the Dominant Environmental Quenching Process in UVCANDELS/COSMOS Groups
- 2023
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Ingår i: Astrophysical Journal. - 0004-637X .- 1538-4357. ; 947:1
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Tidskriftsartikel (refereegranskat)abstract
- We explore how the fraction of quenched galaxies changes in groups of galaxies with respect to the distance to the center of the group, redshift, and stellar mass to determine the dominant process of environmental quenching in 0.2 < z < 0.8 groups. We use new UV data from the UVCANDELS project in addition to existing multiband photometry to derive new galaxy physical properties of the group galaxies from the zCOSMOS 20 k group catalog. Limiting our analysis to a complete sample of log (M*/M⊙) > 10.56 group galaxies, we find that the probability of being quenched increases slowly with decreasing redshift, diverging from the stagnant field galaxy population. A corresponding analysis on how the probability of being quenched increases with time within groups suggests that the dominant environmental quenching process is characterized by slow (∼Gyr) timescales. We find a quenching time of approximately Gyr, consistent with the slow processes of strangulation and delayed-then-rapid quenching although more data are needed to confirm this result.
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| 11. |
- Nag, Abhishek, et al.
(författare)
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Ba3MIr2O9 hexagonal perovskites in the light of spin-orbit coupling and local structural distortions
- 2018
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Ingår i: Physical Review B. - : AMER PHYSICAL SOC. - 2469-9950 .- 2469-9969. ; 97:6
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Tidskriftsartikel (refereegranskat)abstract
- Spin-orbit coupling (SOC) is found to be crucial for understanding themagnetic and electronic properties of 5d transitionmetal oxides. In 5d systems, with Ir5+ ions, where ideally a nonmagnetic J = 0 ground state is expected to be stabilized in the presence of strong SOC, often spontaneous moments are generated due to hopping induced superexchange. This effect is more pronounced when the Ir atoms are close by, as in systems with Ir2O9 dimers in 6H Ba3MIr2O9 compounds where magnetism is an outcome of complex Ir-O-Ir exchange paths, and is strongly influenced by the presence of local distortions. We find that subtle variations in the local structure of Ba3MIr2O9 (M = Mg, Sr, and Ca) lead to markedly differentmagnetic properties. While SOC plays a pivotal role in explaining the insulating ground states of these systems, it is seen that Ba3MgIr2O9, having a P6(3)/mmc symmetry, does not order down to low temperature despite having antiferromagnetic exchange interactions, while Ba3CaIr2O9 shows weak dimer-like features and stabilizes in C2/c' magnetic configuration with no net moment, and Ba3SrIr2O9 possesses a ground state corresponding to themagnetic space groupC2'/c' and exhibits ferromagnet-like features.
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| 12. |
- Nag, Abhishek, et al.
(författare)
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Origin of the Spin-Orbital Liquid State in a Nearly J=0 Iridate Ba3ZnIr2O9
- 2016
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Ingår i: Physical Review Letters. - : American Physical Society. - 0031-9007 .- 1079-7114. ; 116:9
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Tidskriftsartikel (refereegranskat)abstract
- We show using detailed magnetic and thermodynamic studies and theoretical calculations that the ground state of Ba3ZnIr2O9 is a realization of a novel spin-orbital liquid state. Our results reveal that Ba3ZnIr2O9 with Ir5+ (5d(4)) ions and strong spin-orbit coupling (SOC) arrives very close to the elusive J = 0 state but each Ir ion still possesses a weak moment. Ab initio density functional calculations indicate that this moment is developed due to superexchange, mediated by a strong intradimer hopping mechanism. While the Ir spins within the structural Ir2O9 dimer are expected to form a spin-orbit singlet state (SOS) with no resultant moment, substantial frustration arising from interdimer exchange interactions induce quantum fluctuations in these possible SOS states favoring a spin-orbital liquid phase down to at least 100 mK.
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| 13. |
- Puri, Anil Kumar, et al.
(författare)
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Engineered spin-valve type magnetoresistance in Fe3O4-CoFe2O4 core-shell nanoparticles
- 2013
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Ingår i: Applied Physics Letters. - : AIP Publishing. - 0003-6951 .- 1077-3118. ; 103:10, s. 102406-
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Tidskriftsartikel (refereegranskat)abstract
- Naturally occurring spin-valve-type magnetoresistance (SVMR), recently observed in Sr2FeMoO6 samples, suggests the possibility of decoupling the maximal resistance from the coercivity of the sample. Here we present the evidence that SVMR can be engineered in specifically designed and fabricated core-shell nanoparticle systems, realized here in terms of soft magnetic Fe3O4 as the core and hard magnetic insulator CoFe2O4 as the shell materials. We show that this provides a magnetically switchable tunnel barrier that controls the magnetoresistance of the system, instead of the magnetic properties of the magnetic grain material, Fe3O4, and thus establishing the feasibility of engineered SVMR structures.
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