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Instruments / Technical Area	Publication Details	Published
B18-Core EXAFS	Interplay between structural, magnetic, and electronic states in the pyrochlore iridate Eu2Ir2O7 Manjil Das , Sayantika Bhowal , Jhuma Sannigrahi , Abhisek Bandyopadhyay , Anupam Banerjee , Giannantonio Cibin , Dmitry Khalyavin , Niladri Banerjee , Devashibhai Adroja , Indra Dasgupta , Subham Majumdar Physical Review B 105 DOI: 10.1103/PhysRevB.105.134421 Diamond Proposal Number(s): [17752] Show Abstract ▼ Abstract: We address the concomitant metal-insulator transition (MIT) and antiferromagnetic ordering in the novel pyrochlore iridate Eu 2 Ir 2 O 7 by combining x-ray absorption spectroscopy, x-ray and neutron diffractions, and density functional theory (DFT)-based calculations. The temperature dependent powder x-ray diffraction clearly rules out any change in the lattice symmetry below the MIT, nevertheless a clear anomaly in the Ir-O-Ir bond angle and Ir-O bond length is evident at the onset of MIT. From the x-ray absorption near edge structure (XANES) spectroscopic study of Ir- L 3 and L 2 edges, the effective spin-orbit coupling is found to be intermediate, at least quite far from the strong atomic spin-orbit coupling limit. Powder neutron diffraction measurement is in line with an all-in-all-out magnetic structure of the Ir-tetrahedra in this compound, which is quite common among rare-earth pyrochlore iridates. The sharp change in the Ir-O-Ir bond angle around the MIT possibly arises from the exchange striction mechanism, which favors an enhanced electron correlation via weakening of Ir-Ir orbital overlap and an insulating phase below T M I . The theoretical calculations indicate an insulating state for shorter bond angle validating the experimental observation. Our DFT calculations show a possibility of intriguing topological phase below a critical value of the Ir-O distance, which is shorter than the experimentally observed bond length. Therefore, a topological state may be realized in bulk Eu 2 Ir 2 O 7 sample if the Ir-O bond length can be reduced by the application of sufficient external pressure.	Apr 2022
B18-Core EXAFS	Crossover from Kondo semiconductor to metallic antiferromagnet with 5d-electron doping in CeFe2Al10 Rajesh Tripathi , D. T. Adroja , M. R. Lees , A. Sundaresan , S. Langridge , A. Bhattacharyya , V. K. Anand , D. D. Khalyavin , J. Sannigrahi , G. Cibin , A. D. Hillier , R. I. Smith , H. C. Walker , Y. Muro , T. Takabatake Physical Review B 104 DOI: 10.1103/PhysRevB.104.144405 Diamond Proposal Number(s): [17953] Show Abstract ▼ Abstract: We report a systematic study of the 5 d -electron-doped system Ce ( Fe 1 − x Ir x ) 2 Al 10 ( 0 ≤ x ≤ 0.15 ) . With increasing x , the orthorhombic b axis decreases slightly while accompanying changes in a and c leave the unit cell volume almost unchanged. Inelastic neutron scattering, along with thermal and transport measurements, reveal that for the Kondo semiconductor CeFe 2 Al 10 , the low-temperature energy gap, which is proposed to be a consequence of strong c − f hybridization, is suppressed by a small amount of Ir substitution for Fe and that the system adopts a metallic ground state with an increase in the density of states at the Fermi level. The charge or transport gap collapses (at x = 0.04 ) faster than the spin gap with Ir substitution. Magnetic susceptibility, heat capacity, and muon spin relaxation measurements demonstrate that the system undergoes long-range antiferromagnetic order below a Néel temperature T N of 3.1(2) K for x = 0.15 . The ordered moment is estimated to be smaller than 0.07(1) μ B /Ce, although the trivalent state of Ce is confirmed by Ce L 3 -edge x-ray absorption near edge spectroscopy. It is suggested that the c − f hybridization gap, which plays an important role in the unusually high ordering temperatures observed in Ce T 2 Al 10 ( T = Ru and Os), may not be necessary for the onset of magnetic order with a low T N seen here in Ce ( Fe 1 − x Ir x ) 2 Al 10 .	Oct 2021
B18-Core EXAFS	First-order valence transition: Neutron diffraction, inelastic neutron scattering, and x-ray absorption investigations on the double perovskite Ba2PrRu0.9Ir0.1O6 J. Sannigrahi , D. T. Adroja , C. Ritter , W. Kockelmann , A. D. Hillier , K. S. Knight , A. T. Boothroyd , M. Wakeshima , Y. Hinatsu , J. F. W. Mosselmans , S. Ramos Physical Review B 99 DOI: 10.1103/PhysRevB.99.184440 Diamond Proposal Number(s): [63810] Show Abstract ▼ Abstract: Bulk studies have revealed a first-order valence phase transition in Ba 2 PrRu 1 − x Ir x O 6 ( 0.10 ≤ x ≤ 0.25 ), which is absent in the parent compounds with x = 0 ( Pr 3 + ) and x = 1 ( Pr 4 + ), which exhibit antiferromagnetic order with transition temperatures T N = 120 and 72 K, respectively. In the present study, we have used magnetization, heat capacity, neutron diffraction, inelastic neutron scattering, and x-ray absorption measurements to investigate the nature of the Pr ion in x = 0.1 . The magnetic susceptibility and heat capacity of x = 0.1 show a clear sign of the first-order valence phase transition below 175 K, where the Pr valence changes from 3+ to 4+. Neutron diffraction analysis reveals that x = 0.1 crystallizes in a monoclinic structure with space group P 2 1 / n at 300 K, but below 175 K two phases coexist, the monoclinic having the Pr ion in a 3+ valence state and a cubic one ( F m ¯ 3 m ) having the Pr ion in a 4+ valence state. Clear evidence of an antiferromagnetic ordering of the Pr and Ru moments is found in the monoclinic phase of the x = 0.1 compound below 110 K in the neutron diffraction measurements. Meanwhile, the cubic phase remains paramagnetic down to 2 K, a temperature below which heat capacity and susceptibility measurements reveal a ferromagnetic ordering. High energy inelastic neutron scattering data reveal well-defined high-energy magnetic excitations near 264 meV at temperatures below the valence transition. Low energy INS data show a broad magnetic excitation centered at 50 meV above the valence transition, but four well-defined magnetic excitations at 7 K. The high energy excitations are assigned to the Pr 4 + ions in the cubic phase and the low energy excitations to the Pr 3 + ions in the monoclinic phase. Further direct evidence of the Pr valence transition has been obtained from the x-ray absorption spectroscopy. The results on the x = 0.1 compound are compared with those for x = 0 and 1.	May 2019
I05-ARPES	Multiband one-dimensional electronic structure and spectroscopic signature of tomonaga-luttinger liquid behavior in K2Cr3As3 Matthew D. Watson , Yu Feng , Christopher Nicholson , Claude Monney , Jonathon Riley , Hideaki Iwasawa , Keith Refson , Vincent Sacksteder , Devashibhai Adroja , Jun Zhao , Moritz Hoesch Physical Review Letters 118, 097002 DOI: 10.1103/PhysRevLett.118.097002 Diamond Proposal Number(s): [13797, 14572] Open Access Show Abstract ▼ Abstract: We present angle-resolved photoemission spectroscopy measurements of the quasi-one-dimensional superconductor K2Cr3As3. We find that the Fermi surface contains two Fermi surface sheets, with linearly dispersing bands not displaying any significant band renormalizations. The one-dimensional band dispersions display a suppression of spectral intensity approaching the Fermi level according to a linear power law, over an energy range of ∼200 meV. This is interpreted as a signature of Tomonoga-Luttinger liquid physics, which provides a new perspective on the possibly unconventional superconductivity in this family of compounds.	Mar 2017
I11-High Resolution Powder Diffraction	Spontaneous structural distortion of the metallic Shastry-Sutherland system DyB4 by quadrupole-spin-lattice coupling H. Sim , S. Lee , K.-P. Hong , J. Jeong , J. R. Zhang , T. Kamiyama , D. T. Adroja , C. A. Murray , S. P. Thompson , F. Iga , S. Ji , D. Khomskii , J.-G. Park Physical Review B 94 DOI: 10.1103/PhysRevB.94.195128 Diamond Proposal Number(s): [12470] Show Abstract ▼ Abstract: DyB4 has a two-dimensional Shastry-Sutherland (Sh-S) lattice with strong Ising character of the Dy ions. Despite the intrinsic frustrations, it undergoes two successive transitions: a magnetic ordering at TN=20K and a quadrupole ordering at TQ=12.5K. From high-resolution neutron and synchrotron x-ray powder diffraction studies, we have obtained full structural information on this material in all phases and demonstrate that structural modifications occurring at quadrupolar transition lead to the lifting of frustrations inherent in the Sh-S model. Our paper thus provides a complete experimental picture of how the intrinsic frustration of the Sh-S lattice can be lifted by the coupling to quadrupole moments. We show that two other factors, i.e., strong spin-orbit coupling and long-range Ruderman-Kittel-Kasuya-Yosida (RKKY) interaction in metallic DyB4, play an important role in this behavior.	Nov 2016
B18-Core EXAFS	Competing 4f-electron dynamics in Ce(Ru_{1−x}Fe_{x})_{2}Al_{10} (0≤x≤1.0): Magnetic ordering emerging from the Kondo semiconducting state D. T. Adroja , A. D. Hillier , Y. Muro , J. Kajino , T. Takabatake , P. Peratheepan , A. M. Strydom , P. P. Deen , F. Demmel , J. R. Stewart , J. W. Taylor , R. I. Smith , S. Ramos , M. A. Adams Physical Review B 87 (22) DOI: 10.1103/PhysRevB.87.224415 Show Abstract ▼ Abstract: We have carried out muon spin relaxation (μSR), neutron diffraction, and inelastic neutron scattering (INS) investigations on polycrystalline samples of Ce(Ru1−xFex)2Al10 (x=0, 0.3, 0.5, 0.8, and 1) to investigate the nature of the ground state (magnetic ordered versus paramagnetic) and the origin of the spin-gap formation as evident from the bulk measurements in the end members. Our zero-field μSR spectra clearly reveal coherent two-frequency oscillations at low temperature in x=0, 0.3, and 0.5 samples, which confirm the long-range magnetic ordering of the Ce moment with Nèel temperature TN=27, 26, and 21 K, respectively. On the other hand, the μSR spectra of x=0.8 and x=1 down to 1.4 K and 0.045 K, respectively, exhibit a temperature-independent Kubo-Toyabe term, confirming a paramagnetic ground state. The long-range magnetic ordering in x=0.5 below 21 K has been confirmed through the neutron diffraction study. INS measurements of x=0 clearly reveal the presence of a sharp inelastic excitation near 8 meV between 5 K and 26 K, due to an opening of a gap in the spin excitation spectrum, which transforms into a broad response at and above 30 K. Interestingly, at 4.5 K, the spin-gap excitation broadens in x=0.3 and exhibits two clear peaks at 8.4(3) and 12.0(5) meV in x=0.5. In the x=0.8 sample, which remains paramagnetic down to 1.2 K, there is a clear signature of a spin gap of 10–12 meV at 7 K, with a strong wave-vector–dependent intensity. Evidence of a spin gap of 12.5(5) meV has also been found in x=1. The observation of a spin gap in the paramagnetic samples (x=0.8 and 1) is an interesting finding in this study, and it challenges our understanding of the origin of the semiconducting gap in CeT2Al10 (T = Ru and Os) compounds in terms of a hybridization gap opening only a small part of the Fermi surface, gapped spin waves, or a spin-dimer gap.	Jun 2013

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