| 1. |
- Edberg, Richard, et al.
(författare)
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Dipolar spin ice under uniaxial pressure
- 2019
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Ingår i: Physical Review B. - : American Physical Society. - 2469-9950 .- 2469-9969. ; 100:14
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Tidskriftsartikel (refereegranskat)abstract
- The magnetically frustrated spin ice family of materials is host to numerous exotic phenomena such as magnetic monopole excitations and macroscopic residual entropy extending to low temperature. A finite-temperature ordering transition in the absence of applied fields has not been experimentally observed in the classical spin ice materials Dy2Ti2O7 and Ho2Ti2O7. Such a transition could be induced by the application of pressure, and in this work we consider the effects of uniaxial pressure on classical spin ice systems. Theoretically, we find that the pressure-induced ordering transition in Dy2Ti2O7 is strongly affected by the dipolar interaction. We also report measurements of the neutron structure factor of Ho2Ti2O7 under pressure and compare the experimental results to the predictions of our theoretical model.
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| 2. |
- Edberg, Richard, et al.
(författare)
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Effects of uniaxial pressure on the spin ice Ho2Ti2O7
- 2020
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Ingår i: Physical Review B. - : American Physical Society. - 2469-9950 .- 2469-9969. ; 102:18
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Tidskriftsartikel (refereegranskat)abstract
- The spin ice materials Ho2Ti2O7 and Dy2Ti2O7 are experimental and theoretical exemplars of highly frustrated magnetic materials. However, the effects of applied uniaxial pressure are not well studied, and here we report magnetization measurements of Ho2Ti2O7 under uniaxial pressure applied in the [001], [111], and [110] crystalline directions. The basic features are captured by an extension of the dipolar spin ice model. We find a good match between our model and measurements with pressures applied along two of the three directions, and we extend the framework to discuss the influence of crystal misalignment for the third direction. The parameters determined from the magnetization measurements reproduce neutron scattering measurements that we perform under uniaxial pressure applied along the [110] crystalline direction. In the detailed analysis, we include the recently verified susceptibility dependence of the demagnetizing factor. Our work demonstrates the application of a moderate applied pressure to modify the magnetic interaction parameters. The knowledge can be used to predict critical pressures needed to induce new phases and transitions in frustrated materials, and in the case of Ho2Ti2O7 we expect a transition to a ferromagnetic ground state for uniaxial pressures above 3.3 GPa.
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| 3. |
- Edberg, Richard
(författare)
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Emergent magnetic behaviour in the frustrated Yb3Ga5O12 garnet.
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Annan publikation (övrigt vetenskapligt/konstnärligt)abstract
- We report neutron scattering, magnetic susceptibility and Monte Carlo theoretical analysis to verify the short range nature of the magnetic structure and spin-spin correlations in a Yb3Ga5O12 single crystal. The quantum spin state of Yb3+ in Yb3Ga5O12 is verified. The quantum spins organise into a short ranged emergent director state for T < 0.4 K derived from anisotropy and near neighbour exchange. We derive the magnitude of the near neighbour exchange interactions 0.6 K < J1 < 0.7 K,J2 = 0.12 K and the magnitude of the dipolar exchange interaction, D, in the range 0.18 < D < 0.21 K. Certain aspects of the broad experimental dataset can be modelled using a J1D model with ferromagnetic near neighbour spin-spin correlations while other aspects of the data can be accurately reproduced using a J1J2D model with antiferromagnetic near neighbour spin-spin correlation. As such, although we do not quantify all the relevant exchange interactions we nevertheless provide a strong basis for the understanding of the complex Hamiltonian required to fully describe the magnetic state of YbGG.
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| 4. |
- Edberg, Richard
(författare)
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Magnetic monopole relaxation effects probed by modulation calorimetry in small spin-ice samples
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Annan publikation (övrigt vetenskapligt/konstnärligt)abstract
- We use modulation calorimetry to study the heat capacity of small, 30 ng − 10 μg, samples of the classical spin-ice compounds Dy2Ti2O7 and Ho2Ti2O7. This allows us to investigate thermal relaxation effects on timescales corresponding to modulation frequencies of 0.1-100 Hz. We find a strong frequency dependence in the measured heat capacity in this range. Performing dynamic Monte Carlo simulations we verify that the specific heat frequency response has its origin in the slow magnetic monopole dynamics indigenous to spin ice. Our measurements combined with the Monte Carlo simulations gives a new estimate for the timescales of magnetic dynamics in the highly frustrated spin-ice compounds: 20 ms per Monte Carlo step at 4 K in contrast to 2.5 ms mentioned in previous studies by other techniques.
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| 5. |
- Edberg, Richard, 1993-
(författare)
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Spin ice under uniaxial pressure and magnetic frustration in garnets
- 2021
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Frustration is the inability to simultaneously satisfy all interactions. The interest in magnetic frustration has grown during the last decades. The research has among other findings been promoted by the discovery of spin ice which is a frustrated magnetic compound with an exotic ground state and unusual excitations. In this thesis I present theoretical research on spin ice and experimental measurements where uniaxial pressure has been used to search for new magnetic states in spin ice. I also discuss modern reverse Monte Carlo algorithms used for determining magnetic states in frustrated compounds and the magnetic state of ytterbium gallium garnet is investigated. The thesis concludes by presenting the results from modulation calorimetry measurements on small spin-ice samples which can be used to probe the time scales for magnetic excitations in spin-ice compounds.
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| 6. |
- Kottyan, Leah C., et al.
(författare)
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The IRF5-TNPO3 association with systemic lupus erythematosus has two components that other autoimmune disorders variably share.
- 2015
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Ingår i: Human Molecular Genetics. - : Oxford University Press (OUP). - 0964-6906 .- 1460-2083. ; 24:2, s. 582-596
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Tidskriftsartikel (refereegranskat)abstract
- Exploiting genotyping, DNA sequencing, imputation and trans-ancestral mapping, we used Bayesian and frequentist approaches to model the IRF5-TNPO3 locus association, now implicated in two immunotherapies and seven autoimmune diseases. Specifically, in systemic lupus erythematosus (SLE), we resolved separate associations in the IRF5 promoter (all ancestries) and with an extended European haplotype. We captured 3230 IRF5-TNPO3 high-quality, common variants across 5 ethnicities in 8395 SLE cases and 7367 controls. The genetic effect from the IRF5 promoter can be explained by any one of four variants in 5.7 kb (P-valuemeta = 6 × 10(-49); OR = 1.38-1.97). The second genetic effect spanned an 85.5-kb, 24-variant haplotype that included the genes IRF5 and TNPO3 (P-valuesEU = 10(-27)-10(-32), OR = 1.7-1.81). Many variants at the IRF5 locus with previously assigned biological function are not members of either final credible set of potential causal variants identified herein. In addition to the known biologically functional variants, we demonstrated that the risk allele of rs4728142, a variant in the promoter among the lowest frequentist probability and highest Bayesian posterior probability, was correlated with IRF5 expression and differentially binds the transcription factor ZBTB3. Our analytical strategy provides a novel framework for future studies aimed at dissecting etiological genetic effects. Finally, both SLE elements of the statistical model appear to operate in Sjögrens syndrome and systemic sclerosis whereas only the IRF5-TNPO3 gene-spanning haplotype is associated with primary biliary cirrhosis, demonstrating the nuance of similarity and difference in autoimmune disease risk mechanisms at IRF5-TNPO3.
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| 7. |
- Liu, Ke, et al.
(författare)
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X Chromosome Dose and Sex Bias in Autoimmune Diseases
- 2016
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Ingår i: Arthritis & Rheumatology. - : WILEY-BLACKWELL. - 2326-5191 .- 2326-5205. ; 68:5, s. 1290-1300
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Tidskriftsartikel (refereegranskat)abstract
- Objective. More than 80% of autoimmune disease predominantly affects females, but the mechanism for this female bias is poorly understood. We suspected that an X chromosome dose effect accounts for this, and we undertook this study to test our hypothesis that trisomy X (47, XXX; occurring in similar to 1 in 1,000 live female births) would be increased in patients with female-predominant diseases (systemic lupus erythematosus [SLE], primary Sjogrens syndrome [SS], primary biliary cirrhosis, and rheumatoid arthritis [RA]) compared to patients with diseases without female predominance (sarcoidosis) and compared to controls. Methods. All subjects in this study were female. We identified subjects with 47, XXX using aggregate data from single-nucleotide polymorphism arrays, and, when possible, we confirmed the presence of 47, XXX using fluorescence in situ hybridization or quantitative polymerase chain reaction. Results. We found 47, XXX in 7 of 2,826 SLE patients and in 3 of 1,033 SS patients, but in only 2 of 7,074 controls (odds ratio in the SLE and primary SS groups 8.78 [95% confidence interval 1.67-86.79], P = 0.003 and odds ratio 10.29 [95% confidence interval 1.18-123.47], P = 0.02, respectively). One in 404 women with SLE and 1 in 344 women with SS had 47, XXX. There was an excess of 47, XXX among SLE and SS patients. Conclusion. The estimated prevalence of SLE and SS in women with 47, XXX was similar to 2.5 and similar to 2.9 times higher, respectively, than that in women with 46, XX and similar to 25 and similar to 41 times higher, respectively, than that in men with 46, XY. No statistically significant increase of 47, XXX was observed in other female-biased diseases (primary biliary cirrhosis or RA), supporting the idea of multiple pathways to sex bias in autoimmunity.
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| 8. |
- Liu, Ke, et al.
(författare)
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X Chromosome Dose and Sex Bias in Autoimmune Diseases : Increased 47,XXX in Systemic Lupus Erythematosus and Sjögren's Syndrome
- 2016
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Ingår i: Arthritis & Rheumatology. - : Wiley. - 2326-5191 .- 2326-5205. ; 68:5, s. 1290-1300
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Tidskriftsartikel (refereegranskat)abstract
- OBJECTIVE:More than 80% of autoimmune disease is female dominant, but the mechanism for this female bias is poorly understood. We suspected an X chromosome dose effect and hypothesized that trisomy X (47,XXX, 1 in ∼1,000 live female births) would be increased in female predominant diseases (e.g. systemic lupus erythematosus [SLE], primary Sjögren's syndrome [SS], primary biliary cirrhosis [PBC] and rheumatoid arthritis [RA]) compared to diseases without female predominance (sarcoidosis) and controls.METHODS:We identified 47,XXX subjects using aggregate data from single nucleotide polymorphism (SNP) arrays and confirmed, when possible, by fluorescent in situ hybridization (FISH) or quantitative polymerase chain reaction (q-PCR).RESULTS:We found 47,XXX in seven of 2,826 SLE and three of 1,033 SS female patients, but only in two of the 7,074 female controls (p=0.003, OR=8.78, 95% CI: 1.67-86.79 and p=0.02, OR=10.29, 95% CI: 1.18-123.47; respectively). One 47,XXX subject was present for ∼404 SLE women and ∼344 SS women. 47,XXX was present in excess among SLE and SS subjects.CONCLUSION:The estimated prevalence of SLE and SS in women with 47,XXX was respectively ∼2.5 and ∼2.9 times higher than in 46,XX women and ∼25 and ∼41 times higher than in 46,XY men. No statistically significant increase of 47,XXX was observed in other female-biased diseases (PBC or RA), supporting the idea of multiple pathways to sex bias in autoimmunity. This article is protected by copyright. All rights reserved.
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| 9. |
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| 10. |
- Madanian, H., et al.
(författare)
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Solar cycle variations in ion composition in the dayside ionosphere of Titan
- 2016
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Ingår i: Journal of Geophysical Research - Space Physics. - 2169-9380 .- 2169-9402. ; 121:8, s. 8013-8037
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Tidskriftsartikel (refereegranskat)abstract
- One Titanian year spans over two complete solar cycles, and the solar irradiance has a significant effect on ionospheric densities. Solar cycle 24 has been one of the quietest cycles on record. In this paper we show data from the Cassini ion and neutral mass spectrometer (INMS) and the radio and plasma wave science Langmuir probe spanning the time period from early 2005, at the declining phase of solar cycle 23, to late 2015 at the declining phase of solar cycle 24. Densities of different ion species measured by the INMS show a consistent enhancement for high solar activity, particularly near the ionospheric peak. The density enhancement is best seen in primary ion species such as CH3+ rather than heavier ion species such as HCNH+. Unlike at Earth, where the ionosphere and atmosphere thermally expand at high solar activity, at Titan the altitude of the ionospheric peak decreases, indicating that the underlying neutral atmosphere was less extensive. Among the major ion species, CH5+ shows the largest decrease in peak altitude, whereas heavy ions such as C3H5+ show very little decrease. We also calculate the ion production rates using a theoretical model and a simple empirical model using INMS data and show that these effectively predict the increased ion production rates at high solar activity.
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| 11. |
- Richard, M. S., et al.
(författare)
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An empirical approach to modeling ion production rates in Titan's ionosphere I : Ion production rates on the dayside and globally
- 2015
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Ingår i: Journal of Geophysical Research - Space Physics. - 2169-9380 .- 2169-9402. ; 120:2, s. 1264-1280
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Tidskriftsartikel (refereegranskat)abstract
- Titan's ionosphere is created when solar photons, energetic magnetospheric electrons or ions, and cosmic rays ionize the neutral atmosphere. Electron densities generated by current theoretical models are much larger than densities measured by instruments on board the Cassini orbiter. This model density overabundance must result either from overproduction or from insufficient loss of ions. This is the first of two papers that examines ion production rates in Titan's ionosphere, for the dayside and nightside ionosphere, respectively. The first (current) paper focuses on dayside ion production rates which are computed using solar ionization sources (photoionization and electron impact ionization by photoelectrons) between 1000 and 1400km. In addition to theoretical ion production rates, empirical ion production rates are derived from CH4, CH3+, and CH4+ densities measured by the INMS (Ion Neutral Mass Spectrometer) for many Titan passes. The modeled and empirical production rate profiles from measured densities of N-2(+) and CH4+ are found to be in good agreement (to within 20%) for solar zenith angles between 15 and 90 degrees. This suggests that the overabundance of electrons in theoretical models of Titan's dayside ionosphere is not due to overproduction but to insufficient ion losses.
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| 12. |
- Sandberg, L. o., et al.
(författare)
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Design, calibration, and performance of a uniaxial pressure cell for neutron scattering studies of quantum magnetism
- 2023
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Ingår i: Review of Scientific Instruments. - : AIP Publishing. - 0034-6748 .- 1089-7623. ; 94:10
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Tidskriftsartikel (refereegranskat)abstract
- We provide an overview of a pressure cell designed to apply uniaxial pressure to single crystals for the study, by neutron scattering techniques, of strongly correlated magnetic systems and, in particular, quantum magnets. A detailed overview of the pressure cell components, their requirements, and links to the scientific and technical specifications are presented. The pressure cell is able to accommodate a 200 mm(3) single crystal that can be pressurized up to 2 GPa at cryogenic temperatures. The pressure cell is consistent with the requirements of inelastic neutron scattering and, importantly, neutron polarization analysis. A particular strength of the uniaxial pressure cell is the highly uniform and low background for a wide scattering angle of 360(degrees) horizontally and +/- 20(degrees) vertically. We show the performance of the uniaxial pressure cell using a relevant neutron scattering instrument, the polarized diffuse scattering instrument, D7. The experiments confirm that the cell complies with the scientific and technical requirements. This uniaxial pressure cell will provide a useful additional tool in the sample environment suite available for the study of quantum magnetism.
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| 13. |
- Sandberg, Lise Orduk, et al.
(författare)
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Emergent magnetic behavior in the frustrated Yb3Ga5O12 garnet
- 2021
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Ingår i: Physical Review B. - : American Physical Society (APS). - 2469-9950 .- 2469-9969. ; 104:6
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Tidskriftsartikel (refereegranskat)abstract
- We report neutron scattering, magnetic susceptibility and Monte Carlo theoretical analysis to verify the short-range nature of the magnetic structure and spin-spin correlations in a Yb3Ga5O12 single crystal. The quantum spin state of Yb3+ in Yb3Ga5O12 is verified. The quantum spins organize into a short-ranged emergent director state for T < 0.6 K derived from anisotropy and near-neighbor exchange. We derive the magnitude of the nearneighbor exchange interactions 0.6 < J(1) < 0.7 K, J(2) = 0.12 K and the magnitude of the dipolar exchange interaction, D, in the range 0.18 < D < 0.21 K. Certain aspects of the broad experimental dataset can be modeled using a J(1)D model with ferromagnetic near-neighbor spin-spin correlations while other aspects of the data can be accurately reproduced using a J(1)J(2)D model with antiferromagnetic near-neighbor spin-spin correlation. As such, although we do not quantify all the relevant exchange interactions, we nevertheless provide a strong basis for the understanding of the complex Hamiltonian required to fully describe the magnetic state of Yb3Ga5O12.
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