| 1. |
- Oehri, Jacqueline, et al.
(författare)
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Vegetation type is an important predictor of the arctic summer land surface energy budget
- 2022
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Ingår i: Nature Communications. - : Springer Nature. - 2041-1723. ; 13
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Tidskriftsartikel (refereegranskat)abstract
- Despite the importance of high-latitude surface energy budgets (SEBs) for land-climate interactions in the rapidly changing Arctic, uncertainties in their prediction persist. Here, we harmonize SEB observations across a network of vegetated and glaciated sites at circumpolar scale (1994–2021). Our variance-partitioning analysis identifies vegetation type as an important predictor for SEB-components during Arctic summer (June-August), compared to other SEB-drivers including climate, latitude and permafrost characteristics. Differences among vegetation types can be of similar magnitude as between vegetation and glacier surfaces and are especially high for summer sensible and latent heat fluxes. The timing of SEB-flux summer-regimes (when daily mean values exceed 0 Wm−2) relative to snow-free and -onset dates varies substantially depending on vegetation type, implying vegetation controls on snow-cover and SEB-flux seasonality. Our results indicate complex shifts in surface energy fluxes with land-cover transitions and a lengthening summer season, and highlight the potential for improving future Earth system models via a refined representation of Arctic vegetation types.
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| 2. |
- Forslund, Ola Kenji, et al.
(författare)
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Revisiting the A-type antiferromagnet NaNiO2 with muon spin rotation measurements and density functional theory calculations
- 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
- An A-type antiferromagnet, NaNiO2, was examined by means of positive muon spin rotation and relaxation (mu+SR) measurements and first-principles calculations based on a density functional theory (DFT). Below T-N = 20 K, a clear muon spin precession signal was observed in the mu+SR time spectrum recorded under zero field, due to the formation of a static internal magnetic field. The microscopic origin of such an internal field was computed as a sum of dipolar and hyperfine contact fields at the site (0.624, 0, 0.854), where both the muon site and the local spin density at such a site were predicted with DFT calculations. While the computed values were consistent with experimentally obtained ones, in both the antiferromagnetic and the paramagnetic states, the contribution of the hyperfine contact field was shown to be insignificant even below T-N. Finally, measurements at higher temperatures signified thermally activated Na-ion diffusion with E-a = 50(20) meV and D-Na(300K) = 8.8 x 10(-11) cm(2)/s, commonly observed in layered-type compounds.
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| 3. |
- Ohishi, Kazuki, et al.
(författare)
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The internal magnetic field in a ferromagnetic compound Y2Co12P7
- 2023
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Ingår i: Proceedings 15th International Conference on Muon Spin Rotation, Relaxation and Resonance (SR). - : IOP Publishing. ; 2462
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Konferensbidrag (refereegranskat)abstract
- The internal magnetic field in a ferromagnetic compound, Y2Co12P7 with T-C = 150 K, was studied with mu(+) SR using a powder sample down to 2 K. The wTF-mu(+) SR measurements revealed the presence of a sharp magnetic transition at T-C = 151 K, and the ZF-mu(+) SR measurements clarified the formation of static magnetic order below T-C. The presence of two muon spin precession signals in the ZF-mu(+) SR spectrum below TC indicates the existence of the two different muon sites in the lattice. By considering the muon sites and local spin densities at the muon sites predicted with DFT calculations, the ordered magnetic moments of Co were successfully determined.
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| 4. |
- Umegaki, Izumi, et al.
(författare)
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Magnetic phase diagram of Eu 1- x Ca x Co 2 P 2 determined using muon spin rotation and relaxation
- 2024
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Ingår i: Physical Review B. - : American Physical Society (APS). - 2469-9950 .- 2469-9969. ; 109:14
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Tidskriftsartikel (refereegranskat)abstract
- The present study investigated the magnetic nature of a solid solution system consisting of EuCo2P2 and CaCo2P2 using a muon spin rotation and relaxation (mu +SR) technique, which is sensitive to local magnetic environments. The former compound EuCo2P2 is known to enter an incommensurate helical antiferromagnetic (AF) phase below 66 K with neutrons, which was confirmed by the present mu +SR. The magnitude of the ordered Eu moments proposed with neutrons was found to be consistent with that estimated by mu +SR. Furthermore, the latter lattice-collapsed tetragonal phase compound CaCo2P2 is known to enter an A-type AF phase below 90 K, and mu +SR measurements on single crystals revealed the presence of a spin reorientation transition at around 40 K, below which the A-type AF order is likely to be completed. Although all Eu1-xCaxCo2P2 compounds were found to enter a magnetic phase at low temperatures regardless of x, a static ordered state was formed only at the vicinity of the two end compounds, i.e., 0 x 0.4 and 0.9 x 1. Instead, a disordered state, i.e., a random spin-glass state, short-range ordered state, or highly fluctuating state was found in the x range between 0.4 and 0.9, even at the lowest measured temperature (2 K). Together with the magnetization data, our findings clarified the magnetic phase diagram of Eu1-xCaxCo2P2, where a ferromagnetic exchange interaction between Co ions through the Eu2+ ion competes with a direct AF interaction among the Co ions, particularly in the x range between 0.57 and 0.9. This competition yielded multiple phases in Eu1-xCaxCo2P2.
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| 5. |
- Umegaki, Izumi, et al.
(författare)
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Magnetic phase diagram of Eu1−?Ca?Co2P2 determined using muon spin rotation and relaxation
- 2024
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Ingår i: Physical Review B. - : American Physical Society. - 2469-9950 .- 2469-9969. ; 109:14
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Tidskriftsartikel (refereegranskat)abstract
- The present study investigated the magnetic nature of a solid solution system consisting of EuCo2P2 and CaCo2P2 using a muon spin rotation and relaxation (?+SR) technique, which is sensitive to local magnetic environments. The former compound EuCo2P2 is known to enter an incommensurate helical antiferromagnetic (AF) phase below 66 K with neutrons, which was confirmed by the present ?+SR. The magnitude of the ordered Eu moments proposed with neutrons was found to be consistent with that estimated by ?+SR. Furthermore, the latter lattice-collapsed tetragonal phase compound CaCo2P2 is known to enter an ?-type AF phase below 90 K, and ?+SR measurements on single crystals revealed the presence of a spin reorientation transition at around 40 K, below which the ?-type AF order is likely to be completed. Although all Eu1−?Ca?Co2P2 compounds were found to enter a magnetic phase at low temperatures regardless of ?, a static ordered state was formed only at the vicinity of the two end compounds, i.e., 0≤?≤0.4 and 0.9≤?≤1. Instead, a disordered state, i.e., a random spin-glass state, short-range ordered state, or highly fluctuating state was found in the ? range between 0.4 and 0.9, even at the lowest measured temperature (2 K). Together with the magnetization data, our findings clarified the magnetic phase diagram of Eu1−?Ca?Co2P2, where a ferromagnetic exchange interaction between Co ions through the Eu2+ ion competes with a direct AF interaction among the Co ions, particularly in the ? range between 0.57 and 0.9. This competition yielded multiple phases in Eu1−?Ca?Co2P2.
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