| 11. |
- Jena, Suchit Kumar, et al.
(författare)
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Slow spin dynamics of cluster spin-glass spinel Zn(Fe1-xRu (x))(2)O-4 : role of Jahn-Teller active spin-1/2 Cu2+ ions at B-sites
- 2022
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Ingår i: Journal of Physics. - : IOP Publishing Ltd. - 0953-8984 .- 1361-648X. ; 34:40
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Tidskriftsartikel (refereegranskat)abstract
- We report the slow spin dynamics of cluster spin-glass (SG) spinel Zn(Fe1-xRux)(2)O-4 by means of detailed dc-magnetization and ac-susceptibility studies combined with the heat capacity analysis. Two specific compositions (x= 0.5, 0.75) have been investigated in detail along with the substitution of Jahn-Teller (JT) active spin-1/2 Cu2+ ions at B-sites. Measurements based on the frequency and temperature dependence of ac-susceptibility (chi(ac)(f, T)) and the subsequent analysis using the empirical scaling laws such as: (a) Vogel-Fulcher law and (b) Power law reveal the presence of cluster SG state below the characteristic freezing temperature T-SG (17.77 K (x= 0.5) and 14 K (x= 0.75)). Relaxation dynamics of both the compositions follow the non-mean field de Almeida-Thouless (AT)-line approach (T-SG(H) = T-SG(0)(1 - AH(2/phi))), with an ideal value of phi = 3. Nevertheless, the analysis of temperature dependent high field dc-susceptibility, chi(hf) (2 kOe <= H-DC <= 20 kOe, T) provides evidence for Gabay-Toulouse type mixed-phase (coexistence of SG and ferrimagnetic (FiM)) behaviour. Further, in the case of Cu0.2Zn0.8FeRuO4 system, slowly fluctuating magnetic clusters persist even above the short-range FiM ordering temperature (T-FiM) and their volume fraction vanishes completely across similar to 6T(FiM). This particular feature of the dynamics has been very well supported by the time decay of the thermoremanent magnetization and heat-capacity studies. We employed the high temperature series expansion technique to determine the symmetric exchange coupling (J(S)) between the spins which yields J(S) = -3.02 x 10(-5) eV for Cu0.2Zn0.8FeRuO4 representing the dominant intra-sublattice ferromagnetic interactions due to the dilute incorporation of the JT active Cu2+ ions. However, the antiferromagnetic coupling is predominant in ZnFeRuO4 and Cu0.2Zn0.8Fe0.5Ru1.5O4 systems. Finally, we deduced the magnetic phase diagram in the H-DC - T plane using the characteristic parameters obtained from the field variations of both ac- and dc-magnetization measurements.
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| 12. |
- Johansson, Leif, 1945-, et al.
(författare)
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Synchrotron radiation studies of the SiO2/SiC(0001) interface
- 2004
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Ingår i: JOURNAL OF PHYSICS-CONDENSED MATTER ISSN (0953-8984). - : Institute of Physics Publishing (IOPP). - 0953-8984 .- 1361-648X. ; , s. S3423-S3434
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Konferensbidrag (refereegranskat)abstract
- Two questions thought to have a significant effect on SiC-MOS device characteristics are treated. The existence of carbon clusters or carbon containing by-products and the existence of sub-oxides at the SiO2/SiC interface. Results of photoemission studies using synchrotron radiation of the interface of the Si-terminated surface of n-type SiC(0001) crystals are presented. The results show that no carbon clusters or carbon containing by-product can. be detected at the interface of in situ or ex situ grown samples with an oxide layer thickness larger than similar to10 Angstrom. The presence of sub-oxides at the SiO2/SiC interface was predicted in a theoretical calculation and has been revealed in Si 2p core level data by several groups. These results were not unanimous; significant differences in the number of sub-oxide and shifts were reported. A study also including the Si 1s core level and Si KLL Auger transitions was therefore made. These data show the presence of only one sub-oxide at the interface, assigned to Si1+ oxidation states. The SiO2 chemical shift is shown to exhibit a dependence on oxide thickness, similar to but smaller in magnitude than the thickness dependence earlier revealed for SiO2/Si.
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| 13. |
- Mulders, A. M., et al.
(författare)
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On The Interface Magnetism Of Thin Oxidized Co Films : Orbital And Spin Moments
- 2009
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Ingår i: Journal of Physics. - : IOP Publishing. - 0953-8984 .- 1361-648X. ; 21:12, s. 124211-
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Tidskriftsartikel (refereegranskat)abstract
- An x-ray magnetic circular dichroism study of a polycrystalline Co/CoO bilayer is presented. Using both the chemical specificity and surface sensitivity in the core level techniques, we find that uncompensated Co2+ spin moments participate in the remanent ferromagnetic response of the bilayer that has oxygen nearest neighbors. These are likely located at the Co/CoO interface. As intermixing of magnetic species is not present in Co/CoO, it is concluded that the observed interface moments are due to interface roughness. Given their direction, these moments appear to not directly correlate to the exchange bias in these bilayers.
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| 14. |
- Karlsson, Krister
(författare)
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Self-consistent GW combined with single-site dynamical mean field theory for a Hubbard model
- 2005
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Ingår i: Journal of Physics. - : Institute of Physics Publishing (IOPP). - 0953-8984 .- 1361-648X. ; 17:48, s. 7573-7598
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Tidskriftsartikel (refereegranskat)abstract
- We combine the single-site dynamical mean field theory (DMFT) with the non-local GW method. This is done fully self-consistently and we apply our formalism to a one-band Hubbard model. Eventually at self-consistency the full self-energy and polarization operator of the system are retrieved. Some numerical results, in the metallic as well as the insulator regime, are presented and briefly discussed. Depending on the involved interaction (GW) parameters, substantial changes are found when the GW self-energy is incorporated. However, the main point of this work is to demonstrate the applicability of the method, not to make any strict comparison with exact results and experiments.
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| 15. |
- Magnuson, Martin, et al.
(författare)
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Resonant soft x-ray Raman scattering of NiO
- 2002
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Ingår i: Journal of Physics. - : IOP Publishing. - 0953-8984 .- 1361-648X. ; 14:13, s. 3669-3676
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Tidskriftsartikel (refereegranskat)abstract
- Resonant soft x-ray Raman scattering measurements on NiO have been made at photon energies across the Ni 2p absorption edges. The details of the spectral features are identified as Raman scattering due to d-d and charge-transfer excitations. The spectra are interpreted within the single-impurity Anderson model, including multiplets, crystal-field and charge-transfer effects. At threshold excitation, the spectral features consists of triplet-triplet and triplet-singlet transitions of the 3d8 configuration. For excitation energies corresponding to the charge-transfer region in the Ni 2p x-ray absorption spectrum of NiO, the emission spectra are instead dominated by charge-transfer transitions to the 3d9\underline L-1 final state. Comparisons of the final states with other spectroscopical techniques are also made.
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| 16. |
- Mahani, Mohammad Reza, et al.
(författare)
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Trend of the magnetic anisotropy for individual Mn dopants near the (110) GaAs surface
- 2014
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Ingår i: Journal of Physics. - : Institute of Physics (IOP). - 0953-8984 .- 1361-648X. ; 26:39, s. Article ID: 394006-
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Tidskriftsartikel (refereegranskat)abstract
- Using a microscopic finite-cluster tight-binding model, we investigate the trend of the magnetic anisotropy energy as a function of the cluster size for an individual Mn impurity positioned in the vicinity of the (1 1 0) GaAs surface. We present results of calculations for large cluster sizes containing approximately 104 atoms, which have not been investigated so far. Our calculations demonstrate that the anisotropy energy of a Mn dopant in bulk GaAs, found to be non-zero in previous tight-binding calculations, is purely a finite size effect that vanishes with inverse cluster size. In contrast to this, we find that the splitting of the three in-gap Mn acceptor energy levels converges to a finite value in the limit of the infinite cluster size. For a Mn in bulk GaAs this feature is related to the nature of the mean-field treatment of the coupling between the impurity and its nearest neighbor atoms. We also calculate the trend of the anisotropy energy in the sublayers as the Mn dopant is moved away from the surface towards the center of the cluster. Here the use of large cluster sizes allows us to position the impurity in deeper sublayers below the surface, compared to previous calculations. In particular, we show that the anisotropy energy increases up to the fifth sublayer and then decreases as the impurity is moved further away from the surface, approaching its bulk value. The present study provides important insights for experimental control and manipulation of the electronic and magnetic properties of individual Mn dopants at the semiconductor surface by means of advanced scanning tunneling microscopy techniques.
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| 17. |
- Manchon, A., et al.
(författare)
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Currents and torques due to spin-dependent diffraction in ferromagnetic/spin spiral bilayers
- 2008
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Ingår i: Journal of Physics. - : Institute of Physics (IOP). - 0953-8984 .- 1361-648X. ; 20:50, s. 505213-
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Tidskriftsartikel (refereegranskat)abstract
- Spin-dependent transport through the interface between a ferromagnet and a spin spiral is investigated using both ballistic and diffusive models. We find that spin-dependent interferences lead to a new type of diffraction called 'spin diffraction'. It is shown that this spin diffraction leads to local spin and electrical current along the interface, as well as spin transfer torque acting on the spin spiral. This study also emphasizes that in highly inhomogeneous magnetic configurations, diffracted electrons must be taken into account to properly describe the spin transport.
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| 18. |
- Björström, Cecilia M., et al.
(författare)
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Multilayer formation in spin-coated thin films of low-bandgap polyfluorene:PCBM blends
- 2005
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Ingår i: Journal of Physics. - Philadelphia : Institute of Physics Publishing (IOPP). - 0953-8984 .- 1361-648X. ; 17:50, s. L529-L534
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Tidskriftsartikel (refereegranskat)abstract
- Blends of the low-bandgap polymer poly[(9,9-dioctylfluorenyl-2,7-diyl)-co-5,5- (4',7'-di-2-thienyl-2',1',3'-benzothiadiazole] (APFO-3) and the fullerene derivative [6,6]-phenyl–C61–butyric acid methyl ester (PCBM) were spin-coated from chloroform solution into thin films, which were examined with dynamic secondary ion mass spectrometry. For blends with high PCBM content, the depth profiles show composition waves that were caused by surface-directed phase separation during spin-coating. The formation of such multilayer structures by spontaneous self-stratification is likely to have implications for optimization strategies for the performance of organic solar cells
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| 19. |
- Adell, Johan, 1980, et al.
(författare)
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Thermal diffusion of Mn through GaAs overlayers on (Ga, Mn)As
- 2011
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Ingår i: Journal of Physics. - : Institute of Physics Publishing (IOPP). - 0953-8984 .- 1361-648X. ; 23:8
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Tidskriftsartikel (refereegranskat)abstract
- Thermally stimulated diffusion of Mn through thin layers of GaAs has been studied by x-ray photoemission. (Ga, Mn)As samples with 5 at% Mn were capped with 4, 6 and 8 monolayer (ML) GaAs, and Mn diffusing through the GaAs was trapped on the surface by means of amorphous As. It was found that the out-diffusion is completely suppressed for an 8 ML thick GaAs film. The short diffusion length is attributed to an electrostatic barrier formed at the (Ga, Mn)As/GaAs interface.
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| 20. |
- Ahlström, Bodil, 1968, et al.
(författare)
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Prediction of structures and gel transitions in systems of colloids with moderate-range attractions
- 2007
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Ingår i: Journal of Physics. Condensed Matter. - : IOP Publishing. - 0953-8984 .- 1361-648X. ; 19, s. 036102-036117
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Tidskriftsartikel (refereegranskat)abstract
- Predictions of glass transitions from the idealized mode-coupling theory (MCT) are tested for systems with intermediate-range particle attractions. Liquid structure input to MCT is provided by the Asakura–Oosawa (AO) theory for the depletion interaction, used as an idealized model for structures in colloid–polymer mixtures. The effective one-component formulation of the AO theory is verified to capture the complete pair structure found from the binary version of the theory also for polymer–colloid size ratios somewhat larger than those for which an exact mapping of the two descriptions holds. The Percus–Yevick theory is shown to provide an accurate structural input to MCT, at least in the single-phase fluid region. With this combination of theories, very reasonable predictions for locations of glassy states in the experimental phase diagram are obtained for polymer–colloid size ratios somewhat larger than have been considered before. Simple approximations are also suggested for extracting the remaining pair structure from calculations of the one-component AO theory.
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