| 1. |
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| 2. |
- Banerjee, Mitali, et al.
(författare)
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Magnetism in FeNiW disordered alloys : Experiment and theory
- 2010
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Ingår i: Journal of Magnetism and Magnetic Materials. - : Elsevier BV. - 0304-8853 .- 1873-4766. ; 322:21, s. 3558-3564
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Tidskriftsartikel (refereegranskat)abstract
- We report here an experimental study of magnetization of FeNiW alloys at different compositions. We have studied variation of magnetization with temperature (at low external fields) and magnetic field (at low temperatures). The alloy shows para to ferromagnetic transitions across the composition range. We do not find any indication of the spin-glass phase. We have supplemented the experimental work with theoretical analysis using the first-principles tight-binding linear muffin-tin orbitals based augmented space recursion method. Our theoretical estimates of magnetic moment and Curie temperatures agree well with experiment. Our mean-field phase analysis also does not indicate the possibility of a spin-glass.
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| 3. |
- Banerjee, Mitali, et al.
(författare)
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Magnetism in NiFeMo disordered alloys : Experiment and theory
- 2010
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Ingår i: Physica. B, Condensed matter. - : Elsevier BV. - 0921-4526 .- 1873-2135. ; 405:20, s. 4287-4293
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Tidskriftsartikel (refereegranskat)abstract
- In this communication we carry out experimental investigation of the behavior of magnetization with temperature and magnetic field of six samples at different compositions of the disordered ternary alloy NiFeMo. We analyze the data using a fist-principles density functional based electronic structure method and a mean-field phase diagram study.
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| 4. |
- Banerjee, Rudra, et al.
(författare)
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Fe3.3Ni83.2Mo13.5 : a likely candidate to show spin-glass behaviour at low temperatures
- 2011
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Ingår i: Journal of Physics. - : IOP Publishing. - 0953-8984 .- 1361-648X. ; 23:10, s. 106002-
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Tidskriftsartikel (refereegranskat)abstract
- Unlike other transition metals alloyed with a non-magnetic metal, alloys of Ni behave rather differently. This is because of the fragility of the local magnetic moment on Ni. NiMo and NiW do not show any spin-glass phase. However, addition of Fe can bolster the moment on Ni. We wish to study whether the alloy Fe3.3Ni83.2Mo13.5, chosen near a composition where mean-field estimates suggest there could be a spin-glass phase, shows such a phase or not.
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| 5. |
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| 6. |
- Pal, Pampa, et al.
(författare)
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Magnetic ordering in Ni-rich NiMn alloys around the multicritical point : Experiment and theory
- 2012
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Ingår i: Physical Review B. Condensed Matter and Materials Physics. - 1098-0121 .- 1550-235X. ; 85:17, s. 174405-
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Tidskriftsartikel (refereegranskat)abstract
- We have carried out an experimental study of Ni-rich NiMn alloys in a series of compositions across the multicritical point and determined the phase diagram within that range. We have observed ferromagnetic long-range order with reentrant spin-glass/ferro-spin-glass phase for x <= 25, an antiferromagnetic long-range order around x similar to 37, and a gradual change from a canonical spin-glass state to a long-range antiferromagnetic phase in the intermediate composition region. In order to explain the experimental observations, we have examined the physical properties from a density functional based first-principals theoretical analysis and used it to understand the experimental results. Using atomic spin dynamics simulations based on the Landau-Lifshitz-Gilbert equation, we have found the aging behavior and anomalously slow relaxation of magnetization in the composition range where experiment observes spin-glassy behavior.
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| 7. |
- Choudhury, Debraj, et al.
(författare)
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Tuning of dielectric properties and magnetism of SrTiO3 by site-specific doping of Mn
- 2011
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Ingår i: Physical Review B. Condensed Matter and Materials Physics. - 1098-0121 .- 1550-235X. ; 84:12, s. 125124-
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Tidskriftsartikel (refereegranskat)abstract
- Combining experiments with first-principles calculations, we show that site-specific doping of Mn into SrTiO(3) has a decisive influence on the dielectric properties of these doped systems. We find that phonon contributions to the dielectric constant invariably decrease sharply on doping at any site. However, a sizable, random dipolar contribution only for Mn at the Sr site arises from a strong off-centric displacement of Mn in spite of Mn being in a non-d(0) state; this leads to a large dielectric constant at higher temperatures and gives rise to a relaxor ferroelectric behavior at lower temperatures. We also investigate magnetic properties in detail and critically reevaluate the possibility of a true multiglass state in such systems.
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| 8. |
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| 9. |
- Herper, Heike C., et al.
(författare)
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Iron porphyrin molecules on Cu(001) : Influence of adlayers and ligands on the magnetic properties
- 2013
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Ingår i: Physical Review B. Condensed Matter and Materials Physics. - 1098-0121 .- 1550-235X. ; 87:17, s. 174425-
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Tidskriftsartikel (refereegranskat)abstract
- The structural and magnetic properties of Fe octaethylporphyrin molecules on Cu(001) have been investigated by means of density functional theory (DFT) methods and x-ray absorption spectroscopy. The molecules have been adsorbed on the bare metal surface and on an oxygen-covered surface, which shows a root 2 x 2 root 2R45 degrees reconstruction. In order to allow for a direct comparison between magnetic moments obtained from sum-rule analysis and DFT, we calculate the spin dipolar term 7T (theta), which is also important in view of the magnetic anisotropy of the molecule. The measured x-ray magnetic circular dichroism shows a strong dependence on the photon incidence angle, which we could relate to a huge value of 7T (theta), e. g., on Cu(001), 7T (theta) amounts to -2.07 mu(B) for normal incidence leading to a reduction of the effective spin moment (m(s) + 7T (theta)). Calculations have also been performed to study the influence of possible ligands such as Cl and O atoms on the magnetic properties of the molecule and the interaction between molecule and surface because the experimental spectra display a clear dependence on the ligand, which is used to stabilize the molecule in the gas phase. Both types of ligands weaken the hybridization between surface and porphyrin molecule and change the magnetic spin state of the molecule, but the changes in the x-ray absorption are clearly related to residual Cl ligands.
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| 10. |
- Igarashi, R. N., et al.
(författare)
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First-principles studies of complex magnetism in Mn nanostructures on the Fe(001) surface
- 2012
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Ingår i: Physical Review B. Condensed Matter and Materials Physics. - 1098-0121 .- 1550-235X. ; 85:1, s. 014436-
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Tidskriftsartikel (refereegranskat)abstract
- The magnetic properties of Mn nanostructures on the Fe(001) surface have been studied using the noncollinear first-principles real space-linear muffin-tin orbital-atomic sphere approximation method within density-functional theory. We have considered a variety of nanostructures such as adsorbed wires, pyramids, and flat and intermixed clusters of sizes varying from two to nine atoms. Our calculations of interatomic exchange interactions reveal the long-range nature of exchange interactions between Mn-Mn and Mn-Fe atoms. We have found that the strong dependence of these interactions on the local environment, the magnetic frustration, and the effect of spin-orbit coupling lead to the possibility of realizing complex noncollinear magnetic structures such as helical spin spiral and half-skyrmion.
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| 11. |
- Jafri, Syed Hassan Mujtaba, et al.
(författare)
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Conductivity engineering of graphene by defect formation
- 2010
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Ingår i: Journal of Physics D. - : IOP Publishing. - 0022-3727 .- 1361-6463. ; 43:4, s. 045404-
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Tidskriftsartikel (refereegranskat)abstract
- Transport measurements have revealed several exotic electronic properties of graphene. The possibility to influence the electronic structure and hence control the conductivity by adsorption or doping with adatoms is crucial in view of electronics applications. Here, we show that in contrast to expectation, the conductivity of graphene increases with increasing concentration of vacancy defects, by more than one order of magnitude. We obtain a pronounced enhancement of the conductivity after insertion of defects by both quantum mechanical transport calculations as well as experimental studies of carbon nano-sheets. Our finding is attributed to the defect induced mid-gap states, which create a region exhibiting metallic behaviour around the vacancy defects. The modification of the conductivity of graphene by the implementation of stable defects is crucial for the creation of electronic junctions in graphene-based electronics devices.
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| 12. |
- Klar, D., et al.
(författare)
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Field-regulated switching of the magnetization of Co-porphyrin on graphene
- 2014
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Ingår i: Physical Review B. Condensed Matter and Materials Physics. - 1098-0121 .- 1550-235X. ; 89:14, s. 144411-
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Tidskriftsartikel (refereegranskat)abstract
- Different magnetic coupling mechanisms have been identied for a few monolayers of Co-porphyrin molecules deposited on a graphene covered Ni(111) single crystal. A relatively strong antiferromagnetic coupling of the first molecular layer via graphene to the Ni crystal in comparison to a weaker inter-molecular coupling gives rise to a complex field-dependent response of this hybrid system. By continuously increasing the magnetic eld strength the net magnetization of the molecular system switches from antiparallel to parallel to the field direction at 2.5 T. Utilizing x-ray absorption spectroscopy and x-ray magnetic circular dichroism, the element specic magnetization and field dependence was probed. The nature of the magnetic couplings is identied by means of density functional theory and orbital dependent susceptibilities.
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| 13. |
- Mudaliar, S., et al.
(författare)
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Efficacy and Safety of the Farnesoid X Receptor Agonist Obeticholic Acid in Patients With Type 2 Diabetes and Nonalcoholic Fatty Liver Disease
- 2013
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Ingår i: Gastroenterology. - : Elsevier BV. - 0016-5085. ; 145:3, s. 574-582
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Tidskriftsartikel (refereegranskat)abstract
- BACKGROUND & AIMS: Obeticholic acid (OCA; INT-747, 6 alpha-ethyl-chenodeoxycholic acid) is a semisynthetic derivative of the primary human bile acid chenodeoxycholic acid, the natural agonist of the farnesoid X receptor, which is a nuclear hormone receptor that regulates glucose and lipid metabolism. In animal models, OCA decreases insulin resistance and hepatic steatosis. METHODS: We performed a double-blind, placebocontrolled, proof-of-concept study to evaluate the effects of OCA on insulin sensitivity in patients with nonalcoholic fatty liver disease and type 2 diabetes mellitus. Patients were randomly assigned to groups given placebo (n = 23), 25 mg OCA (n = 20), or 50 mg OCA (n = 21) once daily for 6 weeks. A 2-stage hyperinsulinemiceuglycemic insulin clamp was used to measure insulin sensitivity before and after the 6-week treatment period. We also measured levels of liver enzymes, lipid analytes, fibroblast growth factor 19, 7 alpha-hydroxy-4-cholesten-3-one (a BA precursor), endogenous bile acids, and markers of liver fibrosis. RESULTS: When patients were given a low-dose insulin infusion, insulin sensitivity increased by 28.0% from baseline in the group treated with 25 mg OCA (P = .019) and 20.1% from baseline in the group treated with 50 mg OCA (P = .060). Insulin sensitivity increased by 24.5% (P = .011) in combined OCA groups, whereas it decreased by 5.5% in the placebo group. A similar pattern was observed in patients given a high-dose insulin infusion. The OCA groups had significant reductions in levels of gamma-glutamyltransferase and alanine aminotransferase and dose-related weight loss. They also had increased serum levels of low-density lipoprotein cholesterol and fibroblast growth factor 19, associated with decreased levels of 7 alpha-hydroxy-4-cholesten-3-one and endogenous bile acids, indicating activation of farnesoid X receptor. Markers of liver fibrosis decreased significantly in the group treated with 25 mg OCA. Adverse experiences were similar among groups. CONCLUSIONS: In this phase 2 trial, administration of 25 or 50 mg OCA for 6 weeks was well tolerated, increased insulin sensitivity, and reduced markers of liver inflammation and fibrosis in patients with type 2 diabetes mellitus and nonalcoholic fatty liver disease. Longer and larger studies are warranted. ClinicalTrials.gov, Number: NCT00501592.
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| 14. |
- Sandell, Anders, et al.
(författare)
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Probing the conduction band edge of transition metal oxides by X-ray absorption spectroscopy
- 2011
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Ingår i: Journal of Electron Spectroscopy and Related Phenomena. - : Elsevier BV. - 0368-2048 .- 1873-2526. ; 183:1-3, s. 107-113
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Tidskriftsartikel (refereegranskat)abstract
- We present a comprehensive picture of how X-ray absorption spectroscopy (XAS) at the O 1s edge, supported by ob initio calculations, can be used to address the electronic properties of the conduction band edges of transition metal oxides. The compounds studied in order to illustrate the method are two of the most versatile transition metal oxides, ZrO2 and TiO2. Special attention is paid to the subtler aspects of the approach, discussing in more detail the kind of information provided and also possible shortcomings and complications. It is shown that the interpretation of the relationship between the Fermi level-referenced O 1s PES peak and the O 1s is XAS spectrum can change depending on the electronic properties of the material under study. In order to fully understand the PES-XAS relationship, supporting information from calculations is essential.
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| 15. |
- Sato, K., et al.
(författare)
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First-principles theory of dilute magnetic semiconductors
- 2010
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Ingår i: Reviews of Modern Physics. - : APS. - 0034-6861 .- 1539-0756. ; 82:2, s. 1633-1690
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Tidskriftsartikel (refereegranskat)abstract
- This review summarizes recent first-principles investigations of the electronic structure and magnetism of dilute magnetic semiconductors (DMSs), which are interesting for applications in spintronics. Details of the electronic structure of transition-metal-doped III-V and II-VI semiconductors are described, especially how the electronic structure couples to the magnetic properties of an impurity. In addition, the underlying mechanism of the ferromagnetism in DMSs is investigated from the electronic structure point of view in order to establish a unified picture that explains the chemical trend of the magnetism in DMSs. Recent efforts to fabricate high-TC DMSs require accurate materials design and reliable TC predictions for the DMSs. In this connection, a hybrid method (ab initio calculations of effective exchange interactions coupled to Monte Carlo simulations for the thermal properties) is discussed as a practical method for calculating the Curie temperature of DMSs. The calculated ordering temperatures for various DMS systems are discussed, and the usefulness of the method is demonstrated. Moreover, in order to include all the complexity in the fabrication process of DMSs into advanced materials design, spinodal decomposition in DMSs is simulated and we try to assess the effect of inhomogeneity in them. Finally, recent works on first-principles theory of transport properties of DMSs are reviewed. The discussion is mainly based on electronic structure theory within the local-density approximation to density-functional theory.
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| 16. |
- Schmitz, D., et al.
(författare)
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The dipole moment of the spin density as a local indicator for phase transitions
- 2014
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Ingår i: Scientific Reports. - : Springer Science and Business Media LLC. - 2045-2322. ; 4, s. 5760-
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Tidskriftsartikel (refereegranskat)abstract
- The intra-atomic magnetic dipole moment - frequently called < T-z > term - plays an important role in the determination of spin magnetic moments by x-ray absorption spectroscopy for systems with nonspherical spin density distributions. In this work, we present the dipole moment as a sensitive monitor to changes in the electronic structure in the vicinity of a phase transiton. In particular, we studied the dipole moment at the Fe2+ and Fe3+ sites of magnetite as an indicator for the Verwey transition by a combination of x-ray magnetic circular dichroism and density functional theory. Our experimental results prove that there exists a local change in the electronic structure at temperatures above the Verwey transition correlated to the known spin reorientation. Furthermore, it is shown that measurement of the dipole moment is a powerful tool to observe this transition in small magnetite nanoparticles for which it is usually screened by blocking effects in classical magnetometry.
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| 17. |
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| 18. |
- Tacchi, S., et al.
(författare)
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Epitaxial Fe films on ZnSe(001): effect of the substrate surface reconstruction on the magnetic anisotropy
- 2012
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Ingår i: Journal of Physics. - : IOP Publishing. - 0953-8984 .- 1361-648X. ; 24:23, s. 236006-
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Tidskriftsartikel (refereegranskat)abstract
- It is well known that Fe films deposited on a c(2 x 2)-reconstructed ZnSe(001) surface show a strong in-plane uniaxial magnetic anisotropy. Here, the effect of the substrate reconstruction on the magnetic anisotropy of Fe has been studied by in situ Brillouin light scattering. We found that the in-plane uniaxial anisotropy is strongly reduced for Fe films grown on a (1 x 1)-unreconstructed ZnSe substrate while the in-plane biaxial one is nearly unaffected by the substrate reconstruction. Calculations of magnetic anisotropy energies within the framework of ab initio density functional theory reveal that the strong suppression of anisotropy at the (1 x 1) interface occurs due to complex atomic relaxations as well as the competing effects originating from magnetocrystalline anisotropy and dipole-dipole interactions. For both sharp and intermixed c(2 x 2) interfaces, the magnetic anisotropy is enhanced compared to the (1 x 1) case due to the further lowering of symmetry. The theoretical results are in agreement with the experimental findings.
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