186 results on '"Rosner, Helge"'
Search Results
2. The superconductivity of Sr2RuO4 under c-axis uniaxial stress
- Author
-
Jerzembeck, Fabian, Røising, Henrik S., Steppke, Alexander, Rosner, Helge, Sokolov, Dmitry A., Kikugawa, Naoki, Scaffidi, Thomas, Simon, Steven H., Mackenzie, Andrew P., and Hicks, Clifford W.
- Published
- 2022
- Full Text
- View/download PDF
3. Electronically driven spin-reorientation transition of the correlated polar metal Ca₃Ru₂O₇
- Author
-
Marković, Igor, Watson, Matthew D., Clark, Oliver J., Mazzola, Federico, Morales, Edgar Abarca, Hooley, Chris A., Rosner, Helge, Polley, Craig M., Balasubramanian, Thiagarajan, Mukherjee, Saumya, Kikugawa, Naoki, Sokolov, Dmitry A., Mackenzie, Andrew P., and King, Phil D. C.
- Published
- 2020
4. Two types of magnetic shape-memory effects from twinned microstructure and magneto-structural coupling in Fe 1+ y Te
- Author
-
Rößler, Sahana, Koz, Cevriye, Wang, Zhaosheng, Skourski, Yurii, Doerr, Mathias, Kasinathan, Deepa, Rosner, Helge, Schmidt, Marcus, Schwarz, Ulrich, Rößler, Ulrich K., and Wirth, Steffen
- Published
- 2019
5. Itinerant ferromagnetism of the Pd-terminated polar surface of PdCoO₂
- Author
-
Mazzola, Federico, Sunko, Veronika, Khim, Seunghyun, Rosner, Helge, Kushwaha, Pallavi, Clark, Oliver J., Bawden, Lewis, Marković, Igor, Kim, Timur K., Hoesch, Moritz, Mackenzie, Andrew P., and King, Phil D. C.
- Published
- 2018
6. Local magnetism in MnSiPt rules the chemical bond
- Author
-
Rosner, Helge, Leithe-Jasper, Andreas, Carrillo-Cabrera, Wilder, Schnelle, Walter, Ackerbauer, Sarah V., Gamza, Monika B., and Grin, Yuri
- Published
- 2018
7. Strong peak in T c of Sr₂RuO₄ under uniaxial pressure
- Author
-
Steppke, Alexander, Zhao, Lishan, Barber, Mark E., Scaffidi, Thomas, Jerzembeck, Fabian, Rosner, Helge, Gibbs, Alexandra S., Maeno, Yoshiteru, Simon, Steven H., Mackenzie, Andrew P., and Hicks, Clifford W.
- Published
- 2017
8. Observation of the Anomalous Hall Effect in a Layered Polar Semiconductor.
- Author
-
Kim, Seo‐Jin, Zhu, Jihang, Piva, Mario M., Schmidt, Marcus, Fartab, Dorsa, Mackenzie, Andrew P., Baenitz, Michael, Nicklas, Michael, Rosner, Helge, Cook, Ashley M., González‐Hernández, Rafael, Šmejkal, Libor, and Zhang, Haijing
- Subjects
ANOMALOUS Hall effect ,ANTIFERROMAGNETIC materials ,CARRIER density ,SEMICONDUCTORS ,MAGNETIC fields ,SYMMETRY breaking ,IONIC conductivity ,SUPERCONDUCTING magnets - Abstract
Progress in magnetoelectric materials is hindered by apparently contradictory requirements for time‐reversal symmetry broken and polar ferroelectric electronic structure in common ferromagnets and antiferromagnets. Alternative routes can be provided by recent discoveries of a time‐reversal symmetry breaking anomalous Hall effect (AHE) in noncollinear magnets and altermagnets, but hitherto reported bulk materials are not polar. Here, the authors report the observation of a spontaneous AHE in doped AgCrSe2, a layered polar semiconductor with an antiferromagnetic coupling between Cr spins in adjacent layers. The anomalous Hall resistivity 3 μΩcm$\mu \Omega \, \textnormal {cm}$ is comparable to the largest observed in compensated magnetic systems to date, and is rapidly switched off when the angle of an applied magnetic field is rotated to ≈80° from the crystalline c‐axis. The ionic gating experiments show that the anomalous Hall conductivity magnitude can be enhanced by modulating the p‐type carrier density. They also present theoretical results that suggest the AHE is driven by Berry curvature due to noncollinear antiferromagnetic correlations among Cr spins, which are consistent with the previously suggested magnetic ordering in AgCrSe2. The results open the possibility to study the interplay of magnetic and ferroelectric‐like responses in this fascinating class of materials. [ABSTRACT FROM AUTHOR]
- Published
- 2024
- Full Text
- View/download PDF
9. Observation of the anomalous Hall effect in a layered polar semiconductor
- Author
-
Kim, Seo-Jin, Zhu, Jihang, Piva, Mario M., Schmidt, Marcus, Fartab, Dorsa, Mackenzie, Andrew P., Baenitz, Michael, Nicklas, Michael, Rosner, Helge, Cook, Ashley M., González-Hernández, Rafael, Šmejkal, Libor, and Zhang, Haijing
- Subjects
Condensed Matter - Materials Science ,Condensed Matter - Mesoscale and Nanoscale Physics ,Mesoscale and Nanoscale Physics (cond-mat.mes-hall) ,Materials Science (cond-mat.mtrl-sci) ,FOS: Physical sciences - Abstract
Progress in magnetoelectric materials is hindered by apparently contradictory requirements for time-reversal symmetry broken and polar ferroelectric electronic structure in common ferromagnets and antiferromagnets. Alternative routes could be provided by recent discoveries of a time-reversal symmetry breaking anomalous Hall effect in noncollinear magnets and altermagnets, but hitherto reported bulk materials are not polar. Here, we report the observation of a spontaneous anomalous Hall effect in doped AgCrSe$_2$, a layered polar semiconductor with an antiferromagnetic coupling between Cr spins in adjacent layers. The anomalous Hall resistivity 3 $\mu\Omega$ cm is comparable to the largest observed in compensated magnetic systems to date, and is rapidly switched off when the angle of an applied magnetic field is rotated to $\sim 80^{\circ}$ from the crystalline $c$-axis. Our ionic gating experiments show that the anomalous Hall conductivity magnitude can be enhanced by modulating the $p$-type carrier density. We also present theoretical results that suggest the anomalous Hall effect is driven by Berry curvature due to noncollinear antiferromagnetic correlations among Cr spins, which are consistent with the previously suggested magnetic ordering in AgCrSe$_2$. Our results open the possibility to study the interplay of magnetic and ferroelectric-like responses in this fascinating class of materials., Comment: 8 pages, 5 figures
- Published
- 2023
10. Direct observation of a uniaxial stress-driven Lifshitz transition in Sr2RuO4
- Author
-
Sunko, Veronika, Abarca Morales, Edgar, Marković, Igor, Barber, Mark E., Milosavljević, Dijana, Mazzola, Federico, Sokolov, Dmitry A., Kikugawa, Naoki, Cacho, Cephise, Dudin, Pavel, Rosner, Helge, Hicks, Clifford W., King, Philip D. C., and Mackenzie, Andrew P.
- Published
- 2019
- Full Text
- View/download PDF
11. Crystal Structures and Twinning of RuBr3.
- Author
-
Prots, Yurii, Rößler, Sahana, Rößler, Ulrich K., Rosner, Helge, Akselrud, Lev, Schmidt, Marcus, Fitch, Andy, and Schwarz, Ulrich
- Subjects
CRYSTAL structure ,TWINNING (Crystallography) ,X-ray diffraction measurement ,DENSITY functional theory ,SPACE groups - Abstract
The concerted experimental and computational study reports on the polymorphic behavior of RuBr3. Highly‐resolved X‐ray powder diffraction measurements of the modification lt‐RuBr3 give direct evidence for peak splitting substantiating an orthorhombic unit cell with additional weak intensities confirming a primitive lattice. The crystal structure of lt‐RuBr3 is determined using the intensities of a "Drilling" individuum. For lt‐RuBr3, findings of density functional theory calculations suggest that the deviation from hexagonal symmetry is mainly driven by electronic correlations. Reinvestigation of the recently reported high‐pressure modification hp‐RuBr3 essentially confirms the rhombohedral BiI3‐type crystal structure (space group R3‾ ${\bar{3}}$). Simulations of the atomic arrangement of hp‐RuBr3 indicate that spin‐orbit coupling and corrections for the van‐der‐Waals dispersive forces are mandatory to reach a reasonable agreement with the experimentally determined crystal structure. [ABSTRACT FROM AUTHOR]
- Published
- 2023
- Full Text
- View/download PDF
12. Comparative 181Ta-NQR Study of Weyl Monopnictides TaAs and TaP: Relevance of Weyl Fermion Excitations.
- Author
-
Tetsuro Kubo, Hiroshi Yasuoka, Dóra, Balázs, Kasinathan, Deepa, Prots, Yurii, Rosner, Helge, Takuto Fujii, Schmidt, Marcus, and Baenitz, Michael
- Abstract
Based on our first detailed
181 Ta nuclear quadrupole resonance (NQR) studies from 2017 on the Weyl semimetal TaP, we now extended our NQR studies to another Ta-based monopnictide TaAs. In the present work, we have determined the temperature-dependent181 Ta-NQR spectra, the spin–lattice relaxation time T1 , and the spin–spin relaxation time T2 . We found the following characteristic features that showed great contrast to what was found in TaP: (1) The quadrupole coupling constant and asymmetry parameter of EFG, extracted from three NQR frequencies, have a strong temperature dependence above ∼80 K that cannot be explained by the density functional theory calculation incorporating the thermal expansion of the lattice. (2) The temperature dependence of the spin–lattice relaxation rate, 1=T1 T, shows a T4 power law behavior above ∼30 K. This is a great contrast with the 1=T1 T ∝ T² behavior found in TaP, which was ascribed to the magnetic excitations at the Weyl nodes with a temperature-dependent orbital hyperfine coupling. (3) Regarding the nuclear spin–spin interaction, we found the spin-echo signal decays with the pulse separation simply by a Lorentzian function in TaAs, but we have observed spin-echo modulations in TaP that is most likely due to the indirect nuclear spin–spin coupling via virtually excited Weyl fermions. From our experimental findings, we conclude that the present NQR results do not show dominant contributions from Weyl fermion excitations in TaAs. [ABSTRACT FROM AUTHOR]- Published
- 2023
- Full Text
- View/download PDF
13. Investigation of Planckian behavior in a high-conductivity oxide: PdCrO2.
- Author
-
Zhakina, Elina, Daou, Ramzy, Maignan, Antoine, McGuinness, Philippa H., König, Markus, Rosner, Helge, Seo-Jin Kim, Seunghyun Khim, Grasset, Romain, Konczykowski, Marcin, Tulipman, Evyatar, Mendez-Valderrama, Juan Felipe, Chowdhury, Debanjan, Berg, Erez, and Mackenzie, Andrew P.
- Subjects
THERMAL conductivity measurement ,FERMI surfaces ,ELASTIC scattering ,HIGH temperatures - Abstract
The layered delafossite metal PdCrO
2 is a natural heterostructure of highly conductive Pd layers Kondo coupled to localized spins in the adjacent Mott insulating CrO2 layers. At high temperatures, T, it has a T-linear resistivity which is not seen in the isostructural but nonmagnetic PdCoO2 . The strength of the Kondo coupling is known, as-grown crystals are extremely high purity and the Fermi surface is both very simple and experimentally known. It is therefore an ideal material platform in which to investigate “Planckian metal” physics. We do this by means of controlled introduction of point disorder, measurement of the thermal conductivity and Lorenz ratio, and studying the sources of its high-temperature entropy. The T-linear resistivity is seen to be due mainly to elastic scattering and to arise from a sum of several scattering mechanisms. Remarkably, this sum leads to a scattering rate within 10% of the Planckian value of kBT/ℏ. [ABSTRACT FROM AUTHOR]- Published
- 2023
- Full Text
- View/download PDF
14. Unconventional magneto-transport in ultrapure PdCoO2 and PtCoO2
- Author
-
Nandi, Nabhanila, Scaffidi, Thomas, Kushwaha, Pallavi, Khim, Seunghyun, Barber, Mark E., Sunko, Veronika, Mazzola, Federico, King, Philip D. C., Rosner, Helge, Moll, Philip J. W., König, Markus, Moore, Joel E., Hartnoll, Sean, and Mackenzie, Andrew P.
- Published
- 2018
- Full Text
- View/download PDF
15. Concentration- and Temperature-Induced Phase Transitions in PrAlO3–SrTiO3 System
- Author
-
Vasylechko, Leonid, Stepchuk, Roman, Prots, Yuri, and Rosner, Helge
- Published
- 2016
- Full Text
- View/download PDF
16. SUPERCONDUCTIVITY: Strong peak in Tc of Sr2RuO4 under uniaxial pressure
- Author
-
Steppke, Alexander, Zhao, Lishan, Barber, Mark E., Scaffidi, Thomas, Jerzembeck, Fabian, Rosner, Helge, Gibbs, Alexandra S., Maeno, Yoshiteru, Simon, Steven H., Mackenzie, Andrew P., and Hicks, Clifford W.
- Published
- 2017
- Full Text
- View/download PDF
17. Influence of the transition-metal substitution on the physical properties of Lu 2− xNi 21B 6 – From Pauli-paramagnetism to weak ferromagnetism
- Author
-
Gumeniuk, Roman, Schnelle, Walter, Burkhardt, Ulrich, Rosner, Helge, and Leithe-Jasper, Andreas
- Published
- 2012
- Full Text
- View/download PDF
18. Direct space structure solution from precession electron diffraction data: Resolving heavy and light scatterers in Pb 13Mn 9O 25
- Author
-
Hadermann, Joke, Abakumov, Artem M., Tsirlin, Alexander A., Filonenko, Vladimir P., Gonnissen, Julie, Tan, Haiyan, Verbeeck, Johan, Gemmi, Mauro, Antipov, Evgeny V., and Rosner, Helge
- Published
- 2010
- Full Text
- View/download PDF
19. Coupled anion and cation ordering in Sr 3RFe 4O 10.5 ( R=Y, Ho, Dy) anion-deficientperovskites
- Author
-
Abakumov, Artem M., D’Hondt, Hans, Rossell, Marta D., Tsirlin, Alexander A., Gutnikova, Olga, Filimonov, Dmitry S., Schnelle, Walter, Rosner, Helge, Hadermann, Joke, Van Tendeloo, Gustaaf, and Antipov, Evgeny V.
- Published
- 2010
- Full Text
- View/download PDF
20. The polar mixed-valent lanthanum iron(II, III) sulfide La 3Fe 2−δS 7: Synthesis, crystal and electronic structure, 57Fe Mößbauer spectra, magnetic susceptibility and electrical resistivity
- Author
-
Mills, Allison M., Bräunling, Daniel, Rosner, Helge, Schnelle, Walter, Peter Sebastian, C., Pöttgen, Rainer, and Ruck, Michael
- Published
- 2009
- Full Text
- View/download PDF
21. The superconductivity of Sr2RuO4 under c-axis uniaxial stress.
- Author
-
Jerzembeck, Fabian, Røising, Henrik S., Steppke, Alexander, Rosner, Helge, Sokolov, Dmitry A., Kikugawa, Naoki, Scaffidi, Thomas, Simon, Steven H., Mackenzie, Andrew P., and Hicks, Clifford W.
- Subjects
SUPERCONDUCTING transition temperature ,SUPERCONDUCTIVITY ,DENSITY of states ,SUPERCONDUCTORS ,CONTRAST effect ,STRESS-strain curves - Abstract
Applying in-plane uniaxial pressure to strongly correlated low-dimensional systems has been shown to tune the electronic structure dramatically. For example, the unconventional superconductor Sr
2 RuO4 can be tuned through a single Van Hove point, resulting in strong enhancement of both Tc and Hc2 . Out-of-plane (c axis) uniaxial pressure is expected to tune the quasi-two-dimensional structure even more strongly, by pushing it towards two Van Hove points simultaneously. Here, we achieve a record uniaxial stress of 3.2 GPa along the c axis of Sr2 RuO4 . Hc2 increases, as expected for increasing density of states, but unexpectedly Tc falls. As a first attempt to explain this result, we present three-dimensional calculations in the weak interaction limit. We find that within the weak-coupling framework there is no single order parameter that can account for the contrasting effects of in-plane versus c-axis uniaxial stress, which makes this new result a strong constraint on theories of the superconductivity of Sr2 RuO4 . In the superconductor Sr2RuO4, in-plane strain is known to enhance both the superconducting transition temperature Tc and upper critical field Hc2, but the effect of out-of-plane strain has not been studied. Here, the authors find that Hc2 is enhanced under out-of-plane strain, but Tc unexpectedly decreases. [ABSTRACT FROM AUTHOR]- Published
- 2022
- Full Text
- View/download PDF
22. Multiband superconductivity in HoNi2B2C
- Author
-
Müller, Karl-Hartmut, Fuchs, Günter, Drechsler, Stefan-Ludwig, Opahle, Ingo, Eschrig, Helmut, Schultz, Ludwig, Behr, Günter, Löser, Wolfgang, Souptel, Dmitri, Wälte, Andreas, Nenkov, Konstantin, Naidyuk, Yuri, and Rosner, Helge
- Published
- 2007
- Full Text
- View/download PDF
23. Heat and charge transport properties of MgB 2
- Author
-
Schneider, Matthias, Lipp, Dieter, Gladun, Alexander, Zahn, Peter, Handstein, Axel, Fuchs, Günter, Drechsler, Stefan-Ludwig, Richter, Manuel, Müller, Karl-Hartmut, and Rosner, Helge
- Published
- 2001
- Full Text
- View/download PDF
24. Electronically driven spin-reorientation transition of the correlated polar metal Ca3Ru2O7.
- Author
-
Marković, Igor, Watson, Matthew D., Clark, Oliver J., Mazzola, Federico, Morales, Edgar Abarca, Hooley, Chris A., Rosner, Helge, Polley, Craig M., Balasubramanian, Thiagarajan, Mukherjee, Saumya, Kikugawa, Naoki, Sokolov, Dmitry A., Mackenzie, Andrew P., and King, Phil D. C.
- Subjects
SPIN-orbit interactions ,SYMMETRY breaking ,FERMI surfaces ,ATOMIC number ,MAGNETIC control - Abstract
The interplay between spin–orbit coupling and structural inversion symmetry breaking in solids has generated much interest due to the nontrivial spin and magnetic textures which can result. Such studies are typically focused on systems where large atomic number elements lead to strong spin–orbit coupling, in turn rendering electronic correlations weak. In contrast, here we investigate the temperature-dependent electronic structure of Ca
3 Ru2 O7 , a 4d oxide metal for which both correlations and spin–orbit coupling are pronounced and in which octahedral tilts and rotations combine to mediate both global and local inversion symmetry-breaking polar distortions. Our angle-resolved photoemission measurements reveal the destruction of a large hole-like Fermi surface upon cooling through a coupled structural and spinreorientation transition at 48 K, accompanied by a sudden onset of quasiparticle coherence. We demonstrate how these result from band hybridization mediated by a hidden Rashba-type spin– orbit coupling. This is enabled by the bulk structural distortions and unlocked when the spin reorients perpendicular to the local symmetry-breaking potential at the Ru sites. We argue that the electronic energy gain associated with the band hybridization is actually the key driver for the phase transition, reflecting a delicate interplay between spin–orbit coupling and strong electronic correlations and revealing a route to control magnetic ordering in solids. [ABSTRACT FROM AUTHOR]- Published
- 2020
- Full Text
- View/download PDF
25. Coexistence of magnetic order and valence fluctuations in the Kondo lattice system Ce$_2$Rh$_3$Sn$_5$
- Author
-
Gamza, Monika, Gumeniuk, Roman, Burkhardt, Ulrich, Schnelle, Walter, Rosner, Helge, Leithe-Jasper, Andreas, and Ślebarski, Andrzej
- Subjects
Condensed Matter - Strongly Correlated Electrons ,J.2 ,Strongly Correlated Electrons (cond-mat.str-el) ,82D40 ,F321 ,FOS: Physical sciences ,Condensed Matter::Strongly Correlated Electrons - Abstract
We report on the electronic band structure, structural, magnetic and thermal properties of Ce$_2$Rh$_3$Sn$_5$. Ce $L_{\mathrm{III}}$-edge XAS spectra give direct evidence for an intermediate valence behaviour. Thermodynamic measurements reveal magnetic transitions at $T_{\mathrm{N1}}\approx$ 2.9 K and $T_{\mathrm{N2}}\approx$ 2.4 K. Electrical resistivity shows behaviour typical for Kondo lattices. The coexistence of magnetic order and valence fluctuations in a Kondo lattice system we attribute to a peculiar crystal structure in which Ce ions occupy two distinct lattice sites. Analysis of the structural features of Ce$_2$Rh$_3$Sn$_5$, together with results of electronic band structure calculations and thermodynamic data indicate that Ce2 ions are in an intermediate valence state with the ground state electronic configuration close to 4$f^0$, whereas Ce1 ions are trivalent (4$f^1$) and contribute to the low temperature magnetic ordering. Thus, our joined experimental and theoretical investigations classify Ce$_2$Rh$_3$Sn$_5$ as a multivalent charge-ordered system., 12 pages with 10 figures (main manuscript) and 2 pages with 2 figures (supplementary information)
- Published
- 2016
26. Electronic structure and magnetic properties of Bi2CuO4
- Author
-
Janson, Oleg and Rosner, Helge
- Published
- 2007
- Full Text
- View/download PDF
27. NMR study of low dimensional spin system Cu 2(PO 3) 2CH 2
- Author
-
Gippius, Andrei A., Morozova, Elena N., Okhotnikov, Kirill S., Baenitz, Michael, Liu, Wei, Huang, Ya-Hi, Schmitt, Miriam, and Rosner, Helge
- Published
- 2007
- Full Text
- View/download PDF
28. Two types of magnetic shape-memory effects from twinned microstructure and magneto-structural coupling in Fe1+yTe.
- Author
-
Rößler, Sahana, Koz, Cevriye, Zhaosheng Wang, Skourski, Yurii, Doerr, Mathias, Kasinathan, Deepa, Rosner, Helge, Schmidt, Marcus, Schwarz, Ulrich, Rößler, Ulrich K., and Wirth, Steffen
- Subjects
SCANNING tunneling microscopy ,ANTIFERROMAGNETIC materials ,ISOTHERMAL transformations ,TWIN boundaries ,MAGNETIC fields - Abstract
A detailed experimental investigation of Fe
1+y Te (y = 0.11, 0.12) using pulsed magnetic fields up to 60 T confirms remarkable magnetic shape-memory (MSM) effects. These effects result from magnetoelastic transformation processes in the low-temperature antiferromagnetic state of these materials. The observation of modulated and finely twinned microstructure at the nanoscale through scanning tunneling microscopy establishes a behavior similar to that of thermoelastic martensite. We identified the observed, elegant hierarchical twinning pattern of monoclinic crystallographic domains as an ideal realization of crossing twin bands. The antiferromagnetism of the monoclinic ground state allows for a magnetic-field–induced reorientation of these twin variants by the motion of one type of twin boundaries. At sufficiently high magnetic fields, we observed a second isothermal transformation process with large hysteresis for different directions of applied field. This gives rise to a second MSM effect caused by a phase transition back to the field-polarized tetragonal lattice state. [ABSTRACT FROM AUTHOR]- Published
- 2019
- Full Text
- View/download PDF
29. New Ag8PtO6: synthesis, crystal structure, physical properties and theoretical analyses.
- Author
-
Thakur, Gohil Singh, Reuter, Hans, Rosner, Helge, Fecher, Gerhard H., Felser, Claudia, and Jansen, Martin
- Subjects
CRYSTAL structure ,TRICLINIC crystal system ,DIAMAGNETISM ,BINARY mixtures - Abstract
We report the synthesis, crystal structure, and basic physical properties of Ag
8 PtO6 , which represents the first silver platinum ternary oxide. The crystalline compound was obtained from appropriate mixtures of the binary constituents under alkaline conditions at high oxygen pressure, while applying relatively mild thermal conditions (573 K). Ag8 PtO6 crystallizes in a new crystal structure in the triclinic system (P1̅). The structure consists of slightly distorted, discrete PtO6 octahedra, which are linked via O–Ag–O dumbbells to form a three dimensional framework. It is a diamagnetic semiconductor with a band gap of 0.9 eV. DFT based calculations confirm an electronic ground state that corresponds to a 5d6 6s0 configuration of the Pt atoms, in accordance with the observed diamagnetism. [ABSTRACT FROM AUTHOR]- Published
- 2019
- Full Text
- View/download PDF
30. Unconventional metallic magnetism in LaCrSb3
- Author
-
Richter, Manuel, Rusz, Jan, Rosner, Helge, Koepernik, Klaus, Opahle, Ingo, Nitzsche, Ulrike, and Eschrig, Helmut
- Published
- 2004
- Full Text
- View/download PDF
31. The spin gap in malachite Cu2(OH)2CO3 and its evolution under pressure
- Author
-
Lebernegg, Stefan, Tsirlin, Alexander A., Janson, Oleg, and Rosner, Helge
- Subjects
Condensed Matter - Strongly Correlated Electrons ,Strongly Correlated Electrons (cond-mat.str-el) ,FOS: Physical sciences ,Condensed Matter::Strongly Correlated Electrons - Abstract
We report on the microscopic magnetic modeling of the spin-1/2 copper mineral malachite at ambient and elevated pressures. Despite the layered crystal structure of this mineral, the ambient-pressure susceptibility and magnetization data can be well described by an unfrustrated quasi-one-dimensional magnetic model. Weakly interacting antiferromagnetic alternating spin chains are responsible for a large spin gap of 120K. Although the intradimer Cu-O-Cu bridging angles are considerably smaller than the interdimer angles, density functional theory (DFT) calculations revealed that the largest exchange coupling of 190K operates within the structural dimers. The lack of the inversion symmetry in the exchange pathways gives rise to sizable Dzyaloshinskii-Moriya interactions which were estimated by full-relativistic DFT+U calculations. Based on available high-pressure crystal structures, we investigate the exchange couplings under pressure and make predictions for the evolution of the spin gap. The calculations evidence that intradimer couplings are strongly pressure-dependent and their evolution underlies the decrease of the spin gap under pressure. Finally, we assess the accuracy of hydrogen positions determined by structural relaxation within DFT and put forward this computational method as a viable alternative to elaborate experiments.
- Published
- 2013
32. Two energy scales of spin dimers in clinoclase Cu3(AsO4)(OH)3
- Author
-
Lebernegg, Stefan, Tsirlin, Alexander A., Janson, Oleg, and Rosner, Helge
- Subjects
Condensed Matter - Strongly Correlated Electrons ,Strongly Correlated Electrons (cond-mat.str-el) ,FOS: Physical sciences - Abstract
Magnetic susceptibility and microscopic magnetic model of the mineral clinoclase Cu3(AsO4)(OH)3 are reported. This material can be well described as a combination of two nonequivalent spin dimers with the sizable magnetic couplings of J about 700 K and J(D2) about 300 K. Based on density functional theory calculations, we pinpoint the location of dimers in the crystal structure. Surprisingly, the largest coupling operates between the structural Cu2O6 dimers. We investigate magnetostructural correlations in Cu2O6 structural dimers, by considering the influence of the hydrogen position on the magnetic coupling. Additionally, we establish the hydrogen positions that were not known so far and analyze the pattern of hydrogen bonding.
- Published
- 2013
33. Itinerant ferromagnetism of the Pd-terminated polar surface of PdCoO2.
- Author
-
Mazzola, Federico, Sunko, Veronika, Seunghyun Khim, Rosner, Helge, Kushwaha, Pallavi, Clark, Oliver J., Bawden, Lewis, Marković, Igor, Kim, Timur K., Hoesch, Moritz, Mackenzie, Andrew P., and King, Phil D. C.
- Subjects
ELECTRONIC structure ,ATOMIC structure ,SEMICONDUCTORS ,SUPERCONDUCTIVITY ,DENSITY functional theory - Abstract
The ability to modulate the collective properties of correlated electron systems at their interfaces and surfaces underpins the burgeoning field of "designer" quantum materials. Here, we show how an electronic reconstruction driven by surface polarity mediates a Stoner-like magnetic instability to itinerant ferromagnetism at the Pd-terminated surface of the nonmagnetic delafossite oxide metal PdCoO
2 . Combining angle-resolved photoemission spectroscopy and density-functional theory calculations, we show how this leads to a rich multiband surface electronic structure. We find similar surface state dispersions in PdCrO2 , suggesting surface ferromagnetism persists in this sister compound despite its bulk antiferromagnetic order. [ABSTRACT FROM AUTHOR]- Published
- 2018
- Full Text
- View/download PDF
34. <tex>(CuCl)LaTa_{2}O_{\text{7}}$</tex> and quantum phase transition in the <tex>(CuX)LaM_{2}O_{7}$</tex> family (X=Cl, Br; M=Nb, Ta)
- Author
-
Tsirlin, Alexander A., Abakumov, Artem M., Ritter, Clemens, and Rosner, Helge
- Subjects
Physics ,Condensed Matter::Strongly Correlated Electrons - Abstract
We apply neutron diffraction, high-resolution synchrotron x-ray diffraction, magnetization measurements, electronic structure calculations, and quantum Monte-Carlo simulations to unravel the structure and magnetism of (CuCl)LaTa2O7. Despite the pseudo-tetragonal crystallographic unit cell, this compound features an orthorhombic superstructure, similar to the Nb-containing (CuX)LaNb2O7 with X = Cl and Br. The spin lattice entails dimers formed by the antiferromagnetic fourth-neighbor coupling J(4), as well as a large number of nonequivalent interdimer couplings quantified by an effective exchange parameter J(eff). In (CuCl)LaTa2O7, the interdimer couplings are sufficiently strong to induce the long-range magnetic order with the Neel temperature T-N similar or equal to 7 K and the ordered magnetic moment of 0.53 mu(B), as measured with neutron diffraction. This magnetic behavior can be accounted for by J(eff)/J(4) similar or equal to 1.6 and J(4) similar or equal to 16 K. We further propose a general magnetic phase diagram for the (CuCl)LaNb2O7-type compounds, and explain the transition from the gapped spin-singlet (dimer) ground state in (CuCl)LaNb2O7 to the long-range antiferromagnetic order in (CuCl)LaTa2O7 and (CuBr)LaNb2O7 by an increase in the magnitude of the interdimer couplings J(eff)/J(4), with the (CuCl)LaM2O7 (M = Nb, Ta) compounds lying on different sides of the quantum critical point that separates the singlet and long-range-ordered magnetic ground states.
- Published
- 2012
35. Short-range order of Br and three-dimensional magnetism in <tex>(CuBr)LaNb_{2}O_{7}$</tex>
- Author
-
Tsirlin, Alexander A., Abakumov, Artem M., Ritter, Clemens, Henry, Paul F., Janson, Oleg, and Rosner, Helge
- Subjects
Condensed Matter - Materials Science ,Condensed Matter - Strongly Correlated Electrons ,Strongly Correlated Electrons (cond-mat.str-el) ,Physics ,Materials Science (cond-mat.mtrl-sci) ,FOS: Physical sciences ,Condensed Matter::Strongly Correlated Electrons - Abstract
We present a comprehensive study of the crystal structure, magnetic structure, and microscopic magnetic model of (CuBr)LaNb2O7, the Br analog of the spin-gap quantum magnet (CuCl)LaNb2O7. Despite similar crystal structures and spin lattices, the magnetic behavior and even peculiarities of the atomic arrangement in the Cl and Br compounds are very different. The high-resolution x-ray and neutron data reveal a split position of Br atoms in (CuBr)LaNb2O7. This splitting originates from two possible configurations developed by [CuBr] zigzag ribbons. While the Br atoms are locally ordered in the 'ab' plane, their arrangement along the 'c' direction remains partially disordered. The predominant and energetically more favorable configuration features an additional doubling of the 'c' lattice parameter that was not observed in (CuCl)LaNb2O7. (CuBr)LaNb2O7 undergoes long-range antiferromagnetic ordering at TN=32 K, which is nearly 70% of the leading exchange coupling J4~48 K. The Br compound does not show any experimental signatures of low-dimensional magnetism, because the underlying spin lattice is three-dimensional. The coupling along the 'c' direction is comparable to the couplings in the 'ab' plane, even though the shortest Cu--Cu distance along 'c' (11.69 A) is three times larger than nearest-neighbor distances in the 'ab' plane (3.55 A). The stripe antiferromagnetic long-range order featuring columns of parallel spins in the 'ab' plane and antiparallel spins along 'c' is verified experimentally and confirmed by the microscopic analysis., Comment: Published version with the more positive title: 18 pages, 17 figures, 6 tables + Supplementary information
- Published
- 2012
36. Nanostructuring of Ba8Ga16Ge30 clathrates
- Author
-
Pachecoa, Vicente, Cardoso--Gil, Raul, Kasinathan, Deepa, Rosner, Helge, Wagner, Maik, Tepech--Carrillo, Lorenzo, Carrillo--Cabrera, Wilder, Meier, Katrin, and Grin, Yuri
- Subjects
Condensed Matter - Materials Science ,Materials Science (cond-mat.mtrl-sci) ,FOS: Physical sciences - Abstract
First thermoelectric properties measurements on bulk nanostructured Ba8Ga16Ge30 clathrate-I are presented. A sol-gel-calcination route was developed for preparing amorphous nanosized precursor oxides. The further reduction of the oxides led to quantitative yield of crystalline nanosized Ba8Ga16Ge30 clathrate-I. TEM investigations show the clathrate nanoparticles retain the size and morphology of the precursor oxides. The clathrate nanoparticles contain mainly thin plates (approx. 300 nm x 300 nm x 50 nm) and a small amount of nanospheres (diameter ~ 10 nm). SAED patterns confirm the clathrate-I structure type for both morphologies. The powders were compacted via Spark Plasma Sintering (SPS) to obtain a bulk nano-structured material. The Seebeck coefficient S, measured on low-density samples (53% of {\delta}x-ray), reaches -145 {\mu}V/k at 375 {\deg}C. The ZT values are quite low (0.02) due to the high resistivity of the sample (two orders of magnitude larger than bulk materials) and the low sample density. The trend of the temperature dependence of S is in agreement with the values obtained from electronic structure calculations and semi-classical Boltzmann transport theory within the constant scattering approximation. The total thermal conductivity (1.61 W/mK), measured on high density samples (93% of {\delta}x-ray), shows a reduction of 20-25% in relation to the bulk materials (2.1 W/mK). A further shaping of the sample for the Seebeck coefficient and electrical conductivity measurements was not possible due to the presence of cracks. An improvement on the design of the pressing tools, loading of the sample and profile of the applied pressure will enhance the mechanical stability of the samples. These investigations are now in progress., Comment: 21 pages, 10 figures
- Published
- 2011
37. Symmetry preserving lattice collapse in tetragonal SrFe_(2-x)Ru_xAs_2 (x = 0, 0.2) -- a combined experimental and theoretical study
- Author
-
Kasinathan, Deepa, Schmitt, Miriam, Koepernik, Klaus, Ormeci, Alim, Meier, Katrin, Schwarz, Ulrich, Hanfland, Michael, Geibel, Christoph, Grin, Yuri, Leithe-Jasper, Andreas, and Rosner, Helge
- Subjects
Condensed Matter - Materials Science ,Materials Science (cond-mat.mtrl-sci) ,FOS: Physical sciences - Abstract
In a joint experimental and theoretical study, we investigate the isostructural collapse from the ambient pressure tetragonal phase to a collapsed tetragonal phase for non-superconducting metallic SrFe2As2 and SrFe_1.8Ru_0.2As_2. The crystallographic details have been studied using X-ray powder diffraction up to 20 GPa pressure in a diamond anvil cell. The structural phase transition occurs at 10 GPa and 9 GPa for SrFe2As2 and SrFe_1.8Ru_0.2As_2, respectively. The changes in the unit cell dimensions are highly anisotropic with a continuous decrease of the c lattice parameter with pressure, while the a-axis length increases until the transition to a collapsed tetragonal phase and then continues to decrease. Across the phase transition, we observe a volume reduction of 5% and 4% for SrFe2As2 and SrFe_1.8Ru_0.2As_2, respectively. We are able to discern that Ru substitution on the Fe-site acts like `chemical pressure' to the system. Density-functional theory-based calculations of the electronic structure and electron localizability indicator are consistent with the experimental observations. Detailed analysis of the electronic structure in k-space and real space reveals As 4pz interlayer bond formation as the driving force of the c/a collapse with a change in the As-As bond length of about 0.35ang., 10 pages, 7 figures
- Published
- 2011
38. Spiral ground state against ferroelectricity in the frustrated magnet BiMnFe2O6
- Author
-
Abakumov, Artem M., Tsirlin, Alexander A., Perez-Mato, Juan Manuel, Petřiček, Vaclav, Rosner, Helge, Yang, Tao, and Greenblatt, Martha
- Subjects
Condensed Matter - Materials Science ,Condensed Matter - Strongly Correlated Electrons ,Strongly Correlated Electrons (cond-mat.str-el) ,Physics ,Materials Science (cond-mat.mtrl-sci) ,FOS: Physical sciences ,Condensed Matter::Strongly Correlated Electrons - Abstract
The spiral magnetic structure and underlying spin lattice of BiMnFe2O6 are investigated by low-temperature neutron powder diffraction and density functional theory band structure calculations. In spite of the random distribution of the Mn3+ and Fe3+ cations, this compound undergoes a transition into an incommensurate antiferromagnetically ordered state below TN ~ 220 K. The magnetic structure is characterized by the propagation vector k=[0,beta,0] with beta ~ 0.14 and the P22_12_11'(0 \beta 0)0s0s magnetic superspace symmetry. It comprises antiferromagnetic helixes propagating along the b-axis. The magnetic moments lie in the ac plane and rotate about pi*(1+beta) ~ 204.8 deg angle between the adjacent magnetic atoms along b. The spiral magnetic structure arises from the peculiar frustrated arrangement of exchange couplings in the ab plane. The antiferromagnetic coupling along the c-axis leads to the cancellation of electric polarization, and results in the lack of ferroelectricity in BiMnFe2O6., Comment: 11 pages, 8 figures, 8 tables
- Published
- 2011
39. CaCu2(SeO3)2Cl2: spin-1/2 Heisenberg chain compound with complex frustrated interchain couplings
- Author
-
Janson, Oleg, Tsirlin, Alexander A., Rosner, Helge, Olenev, Andrei V., Osipova, Elena S., Berdonosov, Peter S., and Dolgikh, Valery A.
- Subjects
Condensed Matter - Strongly Correlated Electrons ,Condensed Matter - Materials Science ,Strongly Correlated Electrons (cond-mat.str-el) ,Materials Science (cond-mat.mtrl-sci) ,FOS: Physical sciences ,Condensed Matter::Strongly Correlated Electrons - Abstract
We report the crystal structure, magnetization measurements, and band-structure calculations for the spin-1/2 quantum magnet CaCu2(SeO3)2Cl2. The magnetic behavior of this compound is well reproduced by a uniform spin-1/2 chain model with the nearest-neighbor exchange of about 133 K. Due to the peculiar crystal structure, spin chains run in the direction almost perpendicular to the structural chains. We find an exotic regime of frustrated interchain couplings owing to two inequivalent exchanges of 10 K each. Peculiar superexchange paths grant an opportunity to investigate bond-randomness effects under partial Cl-Br substitution., Extended version: 9 pages, 7 figures, 4 tables
- Published
- 2010
40. Ab initio modeling of Bose-Einstein condensation in Pb2V3O9
- Author
-
Tsirlin, Alexander A. and Rosner, Helge
- Subjects
Condensed Matter::Quantum Gases ,Condensed Matter - Strongly Correlated Electrons ,Condensed Matter - Materials Science ,Strongly Correlated Electrons (cond-mat.str-el) ,Materials Science (cond-mat.mtrl-sci) ,FOS: Physical sciences ,Condensed Matter::Strongly Correlated Electrons - Abstract
We apply density functional theory band structure calculations and quantum Monte Carlo simulations to investigate the Bose-Einstein condensation in the spin-1/2 quantum magnet Pb2V3O9. In contrast to previous conjectures on the one-dimensional nature of this compound, we present a quasi-two-dimensional model of spin dimers with ferromagnetic and antiferromagnetic interdimer couplings. Our model is well justified microscopically and provides a consistent description of the experimental data on the magnetic susceptibility, high-field magnetization, and field vs. temperature phase diagram. The Bose-Einstein condensation in the quasi-two-dimensional spin system of Pb2V3O9 is largely governed by intralayer interactions, whereas weak interlayer couplings have a moderate effect on the ordering temperature. The proposed computational approach is an efficient tool to analyze and predict high-field properties of quantum magnets., 6 pages, 6 figures, 1 table
- Published
- 2010
41. Bridging frustrated-spin-chain and spin-ladder physics: quasi-one-dimensional magnetism of BiCu2PO6
- Author
-
Tsirlin, Alexander A., Rousochatzakis, Ioannis, Kasinathan, Deepa, Janson, Oleg, Nath, Ramesh, Weickert, Franziska, Geibel, Christoph, L��uchli, Andreas M., and Rosner, Helge
- Subjects
Condensed Matter - Other Condensed Matter ,Condensed Matter - Materials Science ,Condensed Matter - Strongly Correlated Electrons ,Strongly Correlated Electrons (cond-mat.str-el) ,Materials Science (cond-mat.mtrl-sci) ,FOS: Physical sciences ,Condensed Matter::Strongly Correlated Electrons ,Other Condensed Matter (cond-mat.other) - Abstract
We derive and investigate the microscopic model of the quantum magnet BiCu2PO6 using band structure calculations, magnetic susceptibility and high-field magnetization measurements, as well as ED and DMRG techniques. The resulting quasi-one-dimensional spin model is a two-leg AFM ladder with frustrating next-nearest-neighbor couplings along the legs. The individual couplings are estimated from band structure calculations and by fitting the magnetic susceptibility with theoretical predictions, obtained using ED. The nearest-neighbor leg coupling J1, the rung coupling J4, and one of the next-nearest-neighbor couplings J2 amount to 120-150 K, while the second next-nearest-neighbor coupling is J2'~J2/2. The spin ladders do not match the structural chains, and although the next-nearest-neighbor interactions J2 and J2' have very similar superexchange pathways, they differ substantially in magnitude due to a tiny difference in the O-O distances and in the arrangement of non-magnetic PO4 tetrahedra. An extensive ED study of the proposed model provides the low-energy excitation spectrum and shows that the system is in the strong rung coupling regime. The strong frustration by the next-nearest-neighbor couplings leads to a triplon branch with an incommensurate minimum. This is further corroborated by a strong-coupling expansion up to second order in the inter-rung coupling. Based on high-field magnetization measurements, we estimate the spin gap of 32 K and suggest the likely presence of antisymmetric DM anisotropy and inter-ladder coupling J3. We also provide a tentative description of the physics of BiCu2PO6 in magnetic field, in the light of the low-energy excitation spectra and numerical calculations based on ED and DMRG. In particular, we raise the possibility for a rich interplay between one- and two-component Luttinger liquid phases and a magnetization plateau at 1/2 of the saturation value.
- Published
- 2010
42. Microscopic model of (CuCl)LaNb2O7: coupled spin dimers replace a frustrated square lattice
- Author
-
Tsirlin, Alexander A. and Rosner, Helge
- Subjects
Condensed Matter - Strongly Correlated Electrons ,Condensed Matter - Materials Science ,Strongly Correlated Electrons (cond-mat.str-el) ,Materials Science (cond-mat.mtrl-sci) ,FOS: Physical sciences ,Condensed Matter::Strongly Correlated Electrons - Abstract
We present a microscopic model of the spin-gap quantum magnet (CuCl)LaNb2O7 that was previously suggested as a realization of the spin-1/2 frustrated square lattice. Taking advantage of the precise atomic positions from recent crystal structure refinement, we evaluate individual exchange integrals and construct a minimum model that naturally explains all the available experimental data. Surprisingly, the deviation from tetragonal symmetry leads to the formation of spin dimers between fourth neighbors due to a Cu-Cl-Cl-Cu pathway with a leading antiferromagnetic exchange J4 ~ 25 K. The total interdimer exchange amounts to 12 - 15 K. Our model is in agreement with inelastic neutron scattering results and is further confirmed by quantum Monte-Carlo simulations of the magnetic susceptibility and the high-field magnetization. Our results establish (CuCl)LaNb2O7 as a non-frustrated system of coupled spin dimers with predominant antiferromagnetic interactions and provide a general perspective for related materials with unusual low-temperature magnetic properties., 4 pages, 4 figures, 1 table + supplementary
- Published
- 2010
43. beta-Cu2V2O7: a spin-1/2 honeycomb lattice system
- Author
-
Tsirlin, Alexander A., Janson, Oleg, and Rosner, Helge
- Subjects
Condensed Matter - Strongly Correlated Electrons ,Condensed Matter - Materials Science ,Strongly Correlated Electrons (cond-mat.str-el) ,Materials Science (cond-mat.mtrl-sci) ,FOS: Physical sciences - Abstract
We report on band structure calculations and a microscopic model of the low-dimensional magnet beta-Cu2V2O7. Magnetic properties of this compound can be described by a spin-1/2 anisotropic honeycomb lattice model with the averaged coupling \bar J1=60-66 K. The low symmetry of the crystal structure leads to two inequivalent couplings J1 and J1', but this weak spatial anisotropy does not affect the essential physics of the honeycomb spin lattice. The structural realization of the honeycomb lattice is highly non-trivial: the leading interactions J1 and J1' run via double bridges of VO4 tetrahedra between spatially separated Cu atoms, while the interactions between structural nearest neighbors are negligible. The non-negligible inter-plane coupling Jperp~15 K gives rise to the long-range magnetic ordering at TN~26 K. Our model simulations improve the fit of the magnetic susceptibility data, compared to the previously assumed spin-chain models. Additionally, the simulated ordering temperature of 27 K is in remarkable agreement with the experiment. Our study evaluates beta-Cu2V2O7 as the best available experimental realization of the spin-1/2 Heisenberg model on the honeycomb lattice. We also provide an instructive comparison of different band structure codes and computational approaches to the evaluation of exchange couplings in magnetic insulators., 11 pages, 10 figures, 2 tables: revised version, extended description of simulation results
- Published
- 2010
44. Interplay of atomic displacements in the quantum magnet (CuCl)LaNb2O7
- Author
-
Tsirlin, Alexander A., Abakumov, Artem M., Van Tendeloo, Gustaaf, and Rosner, Helge
- Subjects
Condensed Matter - Materials Science ,Condensed Matter - Strongly Correlated Electrons ,Strongly Correlated Electrons (cond-mat.str-el) ,Materials Science (cond-mat.mtrl-sci) ,FOS: Physical sciences - Abstract
We report on the crystal structure of the quantum magnet (CuCl)LaNb2O7 that was controversially described with respect to its structural organization and magnetic behavior. Using high-resolution synchrotron powder x-ray diffraction, electron diffraction, transmission electron microscopy, and band structure calculations, we solve the room-temperature structure of this compound [alpha-(CuCl)LaNb2O7] and find two high-temperature polymorphs. The gamma-(CuCl)LaNb2O7 phase, stable above 640K, is tetragonal with a(sub) = 3.889 A, c(sub) = 11.738 A, and the space group P4/mmm. In the gamma-(CuCl)LaNb2O7 structure, the Cu and Cl atoms are randomly displaced from the special positions along the {100} directions. The beta-phase [a(sub) x 2a(sub) x c(sub), space group Pbmm] and the alpha-phase [2a(sub) x 2a(sub) x c(sub), space group Pbam] are stable between 640 K and 500 K and below 500 K, respectively. The structural changes at 500 K and 640 K are identified as order-disorder phase transitions. The displacement of the Cl atoms is frozen upon the gamma --> beta transformation, while a cooperative tilting of the NbO6 octahedra in the alpha-phase further eliminates the disorder of the Cu atoms. The low-temperature alpha-(CuCl)LaNb2O7 structure thus combines the two types of the atomic displacements that interfere due to the bonding between the Cu atoms and the apical oxygens of the NbO6 octahedra. The precise structural information resolves the controversy between the previous computation-based models and provides the long-sought input for understanding the magnetic properties of (CuCl)LaNb2O7., 12 pages, 10 figures, 5 tables; crystallographic information (cif files) included
- Published
- 2010
45. Frustrated square lattice with spatial anisotropy: crystal structure and magnetic properties of <tex>PbZnVO(PO_{4})_{2}$</tex>
- Author
-
Tsirlin, Alexander A., Nath, Ramesh, Abakumov, Artem M., Shpanchenko, Roman V., Geibel, Christoph, and Rosner, Helge
- Subjects
Condensed Matter - Strongly Correlated Electrons ,Condensed Matter - Materials Science ,Strongly Correlated Electrons (cond-mat.str-el) ,Physics ,Materials Science (cond-mat.mtrl-sci) ,FOS: Physical sciences ,Condensed Matter::Strongly Correlated Electrons - Abstract
Crystal structure and magnetic properties of the layered vanadium phosphate PbZnVO(PO4)2 are studied using x-ray powder diffraction, magnetization and specific heat measurements, as well as band structure calculations. The compound resembles AA'VO(PO4)2 vanadium phosphates and fits to the extended frustrated square lattice model with the couplings J(1), J(1)' between nearest-neighbors and J(2), J(2)' between next-nearest-neighbors. The temperature dependence of the magnetization yields estimates of averaged nearest-neighbor and next-nearest-neighbor couplings, J(1) ~ -5.2 K and J(2) ~ 10.0 K, respectively. The effective frustration ratio alpha=J(2)/J(1) amounts to -1.9 and suggests columnar antiferromagnetic ordering in PbZnVO(PO4)2. Specific heat data support the estimates of J(1) and J(2) and indicate a likely magnetic ordering transition at 3.9 K. However, the averaged couplings underestimate the saturation field, thus pointing to the spatial anisotropy of the nearest-neighbor interactions. Band structure calculations confirm the identification of ferromagnetic J(1), J(1)' and antiferromagnetic J(2), J(2)' in PbZnVO(PO4)2 and yield J(1)'-J(1) ~ 1.1 K in excellent agreement with the experimental value of 1.1 K, deduced from the difference between the expected and experimentally measured saturation fields. Based on the comparison of layered vanadium phosphates with different metal cations, we show that a moderate spatial anisotropy of the frustrated square lattice has minor influence on the thermodynamic properties of the model. We discuss relevant geometrical parameters, controlling the exchange interactions in these compounds, and propose a new route towards strongly frustrated square lattice materials., Comment: 14 pages, 9 figures, 5 tables
- Published
- 2010
46. Interplay of atomic displacement in the quantum magnet <tex>(CuCI)LaNb_{2}O_{7}$</tex>
- Author
-
Tsirlin, Alexander A., Abakumov, Artem M., Van Tendeloo, Gustaaf, and Rosner, Helge
- Subjects
Physics - Abstract
We report on the crystal structure of the quantum magnet CuClLaNb2O7 that was controversially described with respect to its structural organization and magnetic behavior. Using high-resolution synchrotron powder x-ray diffraction, electron diffraction, transmission electron microscopy, and band-structure calculations, we solve the room-temperature structure of this compound -CuClLaNb2O7 and find two high-temperature polymorphs. The -CuClLaNb2O7 phase, stable above 640 K, is tetragonal with asub=3.889 Å, csub =11.738 Å, and the space group P4/mmm. In the -CuClLaNb2O7 structure, the Cu and Cl atoms are randomly displaced from the special positions along the 100 directions. The phase asub2asubcsub, space group Pbmm and the phase 2asub2asubcsub, space group Pbam are stable between 640 K and 500 K and below 500 K, respectively. The structural changes at 500 and 640 K are identified as order-disorder phase transitions. The displacement of the Cl atoms is frozen upon the → transformation while a cooperative tilting of the NbO6 octahedra in the phase further eliminates the disorder of the Cu atoms. The low-temperature -CuClLaNb2O7 structure thus combines the two types of the atomic displacements that interfere due to the bonding between the Cu atoms and the apical oxygens of the NbO6 octahedra. The precise structural information resolves the controversy between the previous computation-based models and provides the long-sought input for understanding CuClLaNb2O7 and related compounds with unusual magnetic properties.
- Published
- 2010
47. Valence of cerium ions in selected ternary compounds from the system Ce-Rh-Sn
- Author
-
Gamza, Monika, Gumeniuk, Roman, Schnelle, Walter, Slebarski, Andrzej, Rosner, Helge, Grin, Yuri, and Burkhardt, Ulrich
- Subjects
F300 - Abstract
Over the last years, intermetallic compounds from the system Ce–Rh–Sn have attracted a considerable attention owing to a rich variety of strongly correlated electron phenomena they exhibit. CeRhSn2, Ce5Rh4Sn10, Ce2Rh3Sn5 and Ce3Rh4Sn13 are magnetically ordered heavy fermion systems [1-5]. Interestingly, for Ce3+xRh4Sn13-x (0.2
- Published
- 2010
48. Doping dependence of the charge distribution of iron pnictides
- Author
-
Lang, Guillaume, Grafe, Hans-Joachim, Manthey, Katarina, Hammerath, Franziska, Paar, Dalibor, Koch, Katrin, Rosner, Helge, Behr, Günther, Werner, Jochen, and Büchner, Bernd
- Subjects
iron pnictides ,superconductivity ,NQR ,Condensed Matter::Superconductivity ,Condensed Matter::Strongly Correlated Electrons - Abstract
We have investigated the evolution, on doping, of the charge distribution in the new LaO1− xFxFeAs superconductor. This is done using 75As Nuclear Quadrupole Resonance (NQR), which is a sensitive local probe of the electric field gradient generated by the charge distribution. A significant increase of the quadrupole frequency is observed when going from the undoped situation to the superconducting region of the phase diagram, reflecting the change in density or spatial distribution of the electrons. This increase cannot be properly accounted for by LDA calculations, even though there is good agreement between theory and experience for the undoped case. We discuss this discrepancy as well as the relation to the superconductivity, i.e., the link to the doping-dependence of the critical temperature.
- Published
- 2009
49. Structural distortion and frustrated magnetic interactions in the layered copper oxychloride [CuCl]LaNb(2)O(7)
- Author
-
Tsirlin, Alexander A. and Rosner, Helge
- Subjects
Condensed Matter - Strongly Correlated Electrons ,Condensed Matter - Materials Science ,Strongly Correlated Electrons (cond-mat.str-el) ,Materials Science (cond-mat.mtrl-sci) ,FOS: Physical sciences ,Condensed Matter::Strongly Correlated Electrons - Abstract
We present a computational study of the layered copper oxychloride [CuCl]LaNb(2)O(7) that has been recently proposed as a spin-1/2 frustrated square lattice compound. Our results evidence an orbitally degenerate ground state for the reported tetragonal crystal structure and reveal a Jahn-Teller-type structural distortion. This distortion heavily changes the local environment of copper -- CuO(2)Cl(2) plaquettes are formed instead of CuO(2)Cl(4) octahedra -- and restores the single-orbital scenario typical for copper oxides and oxyhalides. The calculated distortion is consistent with the available diffraction data and the experimental results on the electric field gradients for the Cu and Cl sites. The band structure suggests a complex three-dimensional spin model with the interactions up to the fourth neighbors. Despite the layered structure of (CuCl)LaNb(2)O(7), the spin system has pronounced one-dimensional features. Yet, sizable interchain interactions lead to the strong frustration and likely cause the spin-gap behavior. Computational estimates of individual exchange couplings are in qualitative agreement with the experimental data., 13 pages, 9 figures, 3 tables
- Published
- 2008
50. Spin ladder compound Pb(0.55)Cd(0.45)V(2)O(5): synthesis and investigation
- Author
-
Tsirlin, Alexander A., Shpanchenko, Roman V., Antipov, Evgeny V., Bougerol, Catherine, Hadermann, Joke, Van Tendeloo, Gustaaf, Schnelle, Walter, and Rosner, Helge
- Subjects
Condensed Matter - Strongly Correlated Electrons ,Condensed Matter - Materials Science ,Strongly Correlated Electrons (cond-mat.str-el) ,Materials Science (cond-mat.mtrl-sci) ,FOS: Physical sciences - Abstract
The complex oxide Pb(0.55)Cd(0.45)V(2)O(5) was synthesized and investigated by means of X-ray powder diffraction, electron diffraction, magnetic susceptibility measurements and band structure calculations. Its structure is similar to that of MV(2)O(5) compounds (M = Na, Ca) giving rise to a spin system of coupled S=1/2 two-leg ladders. Magnetic susceptibility measurements reveal a spin gap-like behavior with \Delta ~ 270 K and a spin singlet ground state. Band structure calculations suggest Pb(0.55)Cd(0.45)V(2)O(5) to be a system of weakly coupled dimers in perfect agreement with the experimental data. Pb(0.55)Cd(0.45)V(2)O(5) provides an example of the modification of the spin system in layered vanadium oxides by cation substitution. Simple correlations between the cation size, geometrical parameters and exchange integrals for the MV(2)O(5)-type oxides are established and discussed., Comment: 8 pages, 7 figures
- Published
- 2007
Catalog
Discovery Service for Jio Institute Digital Library
For full access to our library's resources, please sign in.