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| 2. |
- Kou, R. H., et al.
(författare)
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Charge transfer-tuned magnetism in Nd-substituted Gd5Si4
- 2018
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Ingår i: AIP Advances. - : AIP Publishing. - 2158-3226. ; 8:12
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Tidskriftsartikel (refereegranskat)abstract
- We report a charge-transfer mechanism in tuning of magnetism of Nd-substituted Gd5-xNdxSi4 (x=1 and 2.5) compounds. The X-ray absorption near edge structure measurements demonstrated that Nd substitutions for Gd induce charge transfer of 5d electrons from Gd to Nd. The charge transfer weakens spin-orbital coupling of Gd but strengthens that of Nd. Consequently, the magnetization responses of the substituted compounds to low magnetic fields are increased while their saturation magnetization is reduced. Electronic structure calculations showed that the charge transfer stabilizes a ferromagnetic and a ferrimagnetic structure in the compounds with x = 1 and 2.5, respectively, but that it does not change the 5d-3p hybridization significantly. It is suggested that the charge transfer of 5d electrons may occur in other rare earth-substituted Gd5Si4 compounds allowing for tuning of their magnetism.
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| 3. |
- Hajati, Y, et al.
(författare)
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Improved gas sensing activity in structurally defected bilayer graphene
- 2012
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Ingår i: Nanotechnology. - : IOP Publishing. - 0957-4484 .- 1361-6528. ; 23:50, s. 50550-
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Tidskriftsartikel (refereegranskat)abstract
- Graphene is a two-dimensional material with a capability of gas sensing, which is here shown to be drastically improved by inducing gentle disorder in the lattice. We report that by using a focused ion beam technique, controlled disorder can be introduced into the graphene structure through Ga + ion irradiation. This disorder leads to an increase in the electrical response of graphene to NO 2 gas molecules by a factor of three in an ambient environment (air). Ab initio density functional calculations indicate that NO 2 molecules bind strongly to Stone–Wales defects, where they modify electronic states close to the Fermi level, which in turn influence the transport properties. The demonstrated gas sensor, utilizing structurally defected graphene, shows faster response, higher conductivity changes and thus higher sensitivity to NO 2 as compared to pristine graphene.
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| 4. |
- Haldar, Soumyajyoti, et al.
(författare)
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Fen (n=1–6) clusters chemisorbed on vacancy defects in graphene : Stability, spin-dipole moment, and magnetic anisotropy
- 2014
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Ingår i: Physical Review B. Condensed Matter and Materials Physics. - 1098-0121 .- 1550-235X. ; 89, s. 205411-
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Tidskriftsartikel (refereegranskat)abstract
- In this work, we have studied the chemical and magnetic interactions of Fen (n = 1–6) clusters with vacancy defects (monovacancy to correlated vacancies with six missing C atoms) in a graphene sheet by ab initio density functional calculations combined with Hubbard U corrections for correlated Fe-d electrons. It is found that the vacancy formation energies are lowered in the presence of Fe, indicating an easier destruction of the graphene sheet. Due to strong chemical interactions between Fe clusters and vacancies, a complex distribution of magnetic moments appear on the distorted Fe clusters which results in reduced averaged magnetic moments compared to the free clusters. In addition to that, we have calculated spin-dipole moments and magnetic anisotropy energies. The calculated spin-dipole moments arising from anisotropic spin density distributions vary between positive and negative values, yielding increased or decreased effective moments. Depending on the cluster geometry, the easy axis of magnetization of the Fe clusters shows in-plane or out-of-plane behavior.
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| 5. |
- 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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| 6. |
- 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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