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Uniaxial Magnetic Anisotropy Energy of Fe Wires Embedded in Carbon

01 Jan 2010-
TL;DR: In this article, the magnetic anisotropy energy (MAE) of Fe cylinders embedded within zigzag carbon nanotubes was analyzed and it was shown that the easy axis changes from parallel to perpendicular with respect to the cylinder axis.
Abstract: In this work, we analyze the magnetic anisotropy energy (MAE) of Fe cylinders embedded within zigzagcarbonnanotubes,bymeansofabinitiocalculations.Toseetheinfluenceoftheconfinement,wefixtheFe cylinder diameter and we follow the changes of the MAE as a function of the diameter of the nanotube, which contains the Fe cylinder. Wefind that the easy axis changes from parallel to perpendicular, with respect to the cylinder axis. The orientation change depends quite strongly on the confinement, which indicates a nontrivial dependence of the magnetization direction as function of the nanotube diameter. We alsofind that the MAE is affected by where the Fe cylinder sits with respect to the carbon nanotube, and the coupling between these two structures could also dominate the magnetic response. We analyze the thermal stability of the magnetization orientation of the Fe cylinder close to room temperature.
Citations
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TL;DR: This study presents engineering of orally deliverable nanogels that can target SUMOylation machinery to combat gut inflammation with very high efficacy and shows that plasmid delivery using TAC6-derived nanogel diminished gut inflammation in a murine colitis model.
Abstract: Poor success rates and challenges associated with the current therapeutic strategies of inflammatory bowel disease (IBD) have accelerated the emergence of gene therapy as an alternative treatment option with great promise. However, oral delivery of nucleic acids (NAs) to an inflamed colon is challenged by multiple barriers presented by the gastrointestinal, extracellular and intracellular compartments. Therefore, we screened a series of polyaspartic acid-derived amphiphilic cationic polymers with varied hydrophobicity for their ability to deliver NAs into mammalian cells. Using the most effective TAC6 polymer, we then engineered biocompatible and stable nanogels composed of polyplexes (TAC6, NA) and an anionic polymer, sodium polyaspartate, that were able to deliver the NAs across mammalian cells using caveolae-mediated cellular uptake. We then utilized these nanogels for oral delivery of PIAS1 (protein inhibitor of activated STAT1), a SUMO 3 ligase, encoding plasmid DNA since PIAS1 is a key nodal therapeutic target for IBD due to its ability to control NF-κB-mediated inflammatory signaling. We show that plasmid delivery using TAC6-derived nanogels diminished gut inflammation in a murine colitis model. Therefore, our study presents engineering of orally deliverable nanogels that can target SUMOylation machinery to combat gut inflammation with very high efficacy.

27 citations

Journal ArticleDOI
TL;DR: In this article, the magnetic moments and magnetocrystalline anisotropy energy of bcc-Fe nanowires with z-axis along the (110) direction are calculated in the framework of ab initio theories.
Abstract: The geometric and the electronic structures, the magnetic moments, and the magnetocrystalline anisotropy energy of bcc-Fe nanowires with z-axis along the (110) direction are calculated in the framework of ab initio theories. In particular, we report a systematic study of free standing nanowires with geometries and sizes ranging from diatomic to 1 nm wide with 31 atoms per unit cell. We found that for nanowires with less than 14 atoms per unit cell, the ground-state structure is body-centered tetragonal. We also calculated the contributions of the dipolar magnetic energy to the magnetic anisotropy energy and found that in some cases, this contribution overcomes the magnetocrystalline part, determining thereby the easy axis direction. These results emphasize the importance and competition between both contributions in low dimensional systems.

13 citations

Journal ArticleDOI
TL;DR: In this paper, the stability of small magnetic particles inside magnetic nanotubes was investigated and the results showed that multisegmented nanotube are more efficient to entrap the particles at temperatures up to hundreds of kelvins.
Abstract: During the last years great attention has been given to the encapsulation of magnetic nanoparticles. In this work we investigated the stability of small magnetic particles inside magnetic nanotubes. Multisegmented nanotubes were tested in order to optimize the stability of the particle inside the nanotubes. Our results evidenced that multisegmented nanotubes are more efficient to entrap the particles at temperatures up to hundreds of kelvins.

10 citations

Journal ArticleDOI
TL;DR: In this article, the possibility of confining magnetic nanoparticles inside multisegmented nanotubes by using strong field gradients is considered by means of Monte Carlo simulations, which is reduced to the random walk performed by the nanoparticle on the energy landscape produced by the tube's magnetic field.
Abstract: The possibility of confining magnetic nanoparticles inside multisegmented nanotubes by using strong field gradients is considered by means of Monte Carlo simulations. The problem is reduced to the random walk performed by the nanoparticle on the energy landscape produced by the tube’s magnetic field. The role of tube material, number of segments, and spacer thickness in the amount of time spent by the particle inside the tube is examined, concluding that it is possible to control the encapsulation time by using different architectures.

5 citations

Journal ArticleDOI
Abstract: Tailoring the magnetic properties at atomic-scale is essential in the engineering of modern spintronics devices. One of the main concerns in the novel nanostructured materials design is the decrease of the paid energy in the way of functioning, but allowing to switch between different magnetic states with a relative low-cost energy at the same time. Magnetic anisotropy (MA) energy defines the stability of a spin in the preferred direction and is a fundamental variable in magnetization switching processes. Transition-metal wires are known to develop large, stable spin and orbital magnetic moments together with MA energies that are orders of magnitude larger than in the corresponding solids. Different ways of controlling the MA have been exploited such as alloying, surface charging, and external electrical fields. Here we investigate from a first-principle approach together with dynamic calculations, the surface strain driven mechanism to tune the magnetic properties of deposited nanowires. We consider as a...

4 citations

References
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Journal ArticleDOI
TL;DR: A simple derivation of a simple GGA is presented, in which all parameters (other than those in LSD) are fundamental constants, and only general features of the detailed construction underlying the Perdew-Wang 1991 (PW91) GGA are invoked.
Abstract: Generalized gradient approximations (GGA’s) for the exchange-correlation energy improve upon the local spin density (LSD) description of atoms, molecules, and solids. We present a simple derivation of a simple GGA, in which all parameters (other than those in LSD) are fundamental constants. Only general features of the detailed construction underlying the Perdew-Wang 1991 (PW91) GGA are invoked. Improvements over PW91 include an accurate description of the linear response of the uniform electron gas, correct behavior under uniform scaling, and a smoother potential. [S0031-9007(96)01479-2] PACS numbers: 71.15.Mb, 71.45.Gm Kohn-Sham density functional theory [1,2] is widely used for self-consistent-field electronic structure calculations of the ground-state properties of atoms, molecules, and solids. In this theory, only the exchange-correlation energy EXC › EX 1 EC as a functional of the electron spin densities n"srd and n#srd must be approximated. The most popular functionals have a form appropriate for slowly varying densities: the local spin density (LSD) approximation Z d 3 rn e unif

146,533 citations

Journal ArticleDOI
TL;DR: An efficient scheme for calculating the Kohn-Sham ground state of metallic systems using pseudopotentials and a plane-wave basis set is presented and the application of Pulay's DIIS method to the iterative diagonalization of large matrices will be discussed.
Abstract: We present an efficient scheme for calculating the Kohn-Sham ground state of metallic systems using pseudopotentials and a plane-wave basis set. In the first part the application of Pulay's DIIS method (direct inversion in the iterative subspace) to the iterative diagonalization of large matrices will be discussed. Our approach is stable, reliable, and minimizes the number of order ${\mathit{N}}_{\mathrm{atoms}}^{3}$ operations. In the second part, we will discuss an efficient mixing scheme also based on Pulay's scheme. A special ``metric'' and a special ``preconditioning'' optimized for a plane-wave basis set will be introduced. Scaling of the method will be discussed in detail for non-self-consistent and self-consistent calculations. It will be shown that the number of iterations required to obtain a specific precision is almost independent of the system size. Altogether an order ${\mathit{N}}_{\mathrm{atoms}}^{2}$ scaling is found for systems containing up to 1000 electrons. If we take into account that the number of k points can be decreased linearly with the system size, the overall scaling can approach ${\mathit{N}}_{\mathrm{atoms}}$. We have implemented these algorithms within a powerful package called VASP (Vienna ab initio simulation package). The program and the techniques have been used successfully for a large number of different systems (liquid and amorphous semiconductors, liquid simple and transition metals, metallic and semiconducting surfaces, phonons in simple metals, transition metals, and semiconductors) and turned out to be very reliable. \textcopyright{} 1996 The American Physical Society.

81,985 citations

Journal ArticleDOI
Peter E. Blöchl1
TL;DR: An approach for electronic structure calculations is described that generalizes both the pseudopotential method and the linear augmented-plane-wave (LAPW) method in a natural way and can be used to treat first-row and transition-metal elements with affordable effort and provides access to the full wave function.
Abstract: An approach for electronic structure calculations is described that generalizes both the pseudopotential method and the linear augmented-plane-wave (LAPW) method in a natural way. The method allows high-quality first-principles molecular-dynamics calculations to be performed using the original fictitious Lagrangian approach of Car and Parrinello. Like the LAPW method it can be used to treat first-row and transition-metal elements with affordable effort and provides access to the full wave function. The augmentation procedure is generalized in that partial-wave expansions are not determined by the value and the derivative of the envelope function at some muffin-tin radius, but rather by the overlap with localized projector functions. The pseudopotential approach based on generalized separable pseudopotentials can be regained by a simple approximation.

61,450 citations

Journal ArticleDOI
TL;DR: In this paper, the formal relationship between US Vanderbilt-type pseudopotentials and Blochl's projector augmented wave (PAW) method is derived and the Hamilton operator, the forces, and the stress tensor are derived for this modified PAW functional.
Abstract: The formal relationship between ultrasoft (US) Vanderbilt-type pseudopotentials and Bl\"ochl's projector augmented wave (PAW) method is derived. It is shown that the total energy functional for US pseudopotentials can be obtained by linearization of two terms in a slightly modified PAW total energy functional. The Hamilton operator, the forces, and the stress tensor are derived for this modified PAW functional. A simple way to implement the PAW method in existing plane-wave codes supporting US pseudopotentials is pointed out. In addition, critical tests are presented to compare the accuracy and efficiency of the PAW and the US pseudopotential method with relaxed core all electron methods. These tests include small molecules $({\mathrm{H}}_{2}{,\mathrm{}\mathrm{H}}_{2}{\mathrm{O},\mathrm{}\mathrm{Li}}_{2}{,\mathrm{}\mathrm{N}}_{2}{,\mathrm{}\mathrm{F}}_{2}{,\mathrm{}\mathrm{BF}}_{3}{,\mathrm{}\mathrm{SiF}}_{4})$ and several bulk systems (diamond, Si, V, Li, Ca, ${\mathrm{CaF}}_{2},$ Fe, Co, Ni). Particular attention is paid to the bulk properties and magnetic energies of Fe, Co, and Ni.

57,691 citations

Journal ArticleDOI
TL;DR: A detailed description and comparison of algorithms for performing ab-initio quantum-mechanical calculations using pseudopotentials and a plane-wave basis set is presented in this article. But this is not a comparison of our algorithm with the one presented in this paper.

47,666 citations