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Träfflista för sökning "hsv:(NATURVETENSKAP) hsv:(Fysik) hsv:(Annan fysik) ;pers:(Etz Corina)"

Sökning: hsv:(NATURVETENSKAP) hsv:(Fysik) hsv:(Annan fysik) > Etz Corina

  • Resultat 1-10 av 24
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1.
  • Bergqvist, Lars, et al. (författare)
  • Atomistic spin dynamics of low-dimensional magnets
  • 2013
  • Ingår i: Physical Review B. Condensed Matter and Materials Physics. - : American Physical Society. - 1098-0121 .- 1550-235X. ; 87
  • Tidskriftsartikel (refereegranskat)abstract
    • We investigate the magnetic properties of a range of low-dimensional ferromagnets using a combination of first-principles calculations and atomistic spin dynamics simulations. This approach allows us to evaluate the ground state and finite temperature properties of experimentally well characterized systems such as Co/Cu(111), Co/Cu(001), Fe/Cu(001) and Fe/W(110), for different thicknesses of the magnetic layer. We compare our calculated spin wave spectra with experimental data available in the literature, and find a good quantitative agreement. We also predict magnon spectra for systems for which no experimental data exist at the moment, and estimate the role of temperature effects.
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2.
  • Chico, Jonathan, et al. (författare)
  • First-principles studies of the Gilbert damping and exchange interactions for half-metallic Heuslers alloys
  • 2016
  • Ingår i: Physical Review B. - : American Physical Society. - 2469-9950 .- 2469-9969. ; 93:21
  • Tidskriftsartikel (refereegranskat)abstract
    • Heusler alloys have been intensively studied due to the wide variety of properties that they exhibit. One of these properties is of particular interest for technological applications, i.e., the fact that some Heusler alloys are half-metallic. In the following, a systematic study of the magnetic properties of three different Heusler families Co(2)MnZ, Co(2)FeZ, and Mn(2)VZ with Z = (Al, Si, Ga, Ge) is performed. A key aspect is the determination of the Gilbert damping from first-principles calculations, with special focus on the role played by different approximations, the effect that substitutional disorder and temperature effects. Heisenberg exchange interactions and critical temperature for the alloys are also calculated as well as magnon dispersion relations for representative systems, the ferromagnetic Co2FeSi and the ferrimagnetic Mn2VAl. Correlation effects beyond standard density-functional theory are treated using both the local spin density approximation including the Hubbard U and the local spin density approximation plus dynamical mean field theory approximation, which allows one to determine if dynamical self-energy corrections can remedy some of the inconsistencies which were previously reported for these alloys.
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3.
  • Chico, Jonathan, et al. (författare)
  • Thermally driven domain-wall motion in Fe on W(110)
  • 2014
  • Ingår i: Physical Review B Condensed Matter. - 0163-1829 .- 1095-3795. ; 90:1, s. 014434-
  • Tidskriftsartikel (refereegranskat)abstract
    • It has recently been shown that domain walls (DWs) in ferromagnets can be moved in the presence of thermal gradients. In this work we study the motion of narrow domain walls in low-dimensional systems when subjected to thermal gradients. The system chosen is a monolayer of Fe on W(110) which is known to exhibit a large anisotropy while having a soft exchange, resulting in a very narrow domain wall. The study is performed by means of atomistic spin dynamics simulations coupled to first-principles calculations. By subjecting this system to thermal gradients we observe a temperature-dependent movement of the domain wall. The thermal gradient always makes the domain wall move towards the hotter region of the sample with a velocity proportional to the gradient. Our material specific study is complemented by model simulations to discern the interplay between the thermal gradient, magnetic anisotropy, and the exchange interaction and shows that the larger DW velocities are found for materials with broader domain-wall width. The relatively slow DW motion of the Fe/W(110) system is hence primarily caused by its narrow domain-wall width, which results from its large magnetic anisotropy and soft exchange
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4.
  • Etz, Corina, et al. (författare)
  • Accelerating the switching of magnetic nanoclusters by anisotropy-driven magnetization dynamics
  • 2012
  • Ingår i: Physical Review B Condensed Matter. - 0163-1829 .- 1095-3795. ; 86:22, s. 224401-
  • Tidskriftsartikel (refereegranskat)abstract
    • In this work, the magnetization dynamics of clusters supported on nonmagnetic substrates is shown to exhibit a complex response when subjected to external magnetic fields. The field-driven magnetization reversal of small Co clusters deposited on a Cu(111) surface has been studied by means of first-principles calculations and atomistic spin dynamics simulations. For applied fields ranging from 1 to 10 Tesla, we observe a coherent magnetization reversal with switching times in the range of several tenths of picoseconds to several nanoseconds, depending on the field strength. We find a nonmonotonous dependence of the switching times with respect to the strength of the applied field, which we prove has its origin in the complex magnetic anisotropy landscape of these low-dimensional systems. This effect is shown to be stable for temperatures around 10 K, and is possible to realize over a range of exchange interactions and anisotropy landscapes. Possible experimental routes to achieve this unique switching behavior are discussed
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5.
  • Etz, Corina, et al. (författare)
  • Atomistic spin dynamics and surface magnons
  • 2015
  • Ingår i: Journal of Physics. - : IOP Publishing. - 0953-8984 .- 1361-648X. ; 27:24
  • Forskningsöversikt (refereegranskat)abstract
    • Atomistic spin dynamics simulations have evolved to become a powerful and versatile tool for simulating dynamic properties of magnetic materials. It has a wide range of applications, for instance switching of magnetic states in bulk and nano-magnets, dynamics of topological magnets, such as skyrmions and vortices and domain wall motion. In this review, after a brief summary of the existing investigation tools for the study of magnons, we focus on calculations of spin-wave excitations in low-dimensional magnets and the effect of relativistic and temperature effects in such structures. In general, we find a good agreement between our results and the experimental values. For material specific studies, the atomistic spin dynamics is combined with electronic structure calculations within the density functional theory from which the required parameters are calculated, such as magnetic exchange interactions, magnetocrystalline anisotropy, and Dzyaloshinskii-Moriya vectors.
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6.
  • Etz, Corina, et al. (författare)
  • Indications of weak electronic correlations in SrRuO3 from first-principles calculations
  • 2012
  • Ingår i: Physical Review B Condensed Matter. - 0163-1829 .- 1095-3795. ; 86:6, s. 064441-
  • Tidskriftsartikel (refereegranskat)abstract
    • We provide, by a detailed first-principles investigation, evidence for weak electronic correlations in SrRuO 3. The magnetism in SrRuO 3, in terms of the equilibrium magnetization and critical temperature, is well described by the generalized gradient approximation. Including Hubbard-type correlations results in worse agreement with experiment
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7.
  • Grånäs, Oscar, et al. (författare)
  • Electronic structure, cohesive properties, and magnetism of SrRuO3
  • 2014
  • Ingår i: Physical Review B Condensed Matter. - 0163-1829 .- 1095-3795. ; 90:16, s. 165130-
  • Tidskriftsartikel (refereegranskat)abstract
    • We have performed an extensive test of the ability of density functional theory within several approximations for the exchange-correlation functional, local density approximation + Hubbard U, and local density approximation + dynamic mean field theory to describe magnetic and electronic properties of SrRuO3. We focus on the ferromagnetic phase, illustrating differences between the orthorhombic low-temperature structure versus the cubic high-temperature structure. We assess how magnetism, spectral function, and cohesive properties are affected by methodology, onsite Hubbard U, and double-counting corrections. Further, we compare the impact of the impurity solver on the quasiparticle weight Z, which is in turn compared to experimental results. The spectral functions resulting from the different treatments are also compared to experimental data. Finally, the impact of spin-orbit coupling is studied, allowing us to determine the orbital moments. In the orthorhombic phase, the orbital moments are found to be tilted with respect to the spin moments, emphasizing the importance of taking into account the distortion of the oxygen octahedra
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8.
  • Johansson, Gustav, et al. (författare)
  • Theoretical investigation of magnons in Fe-Ga alloys
  • 2023
  • Ingår i: Physical Review B. - : American Physical Society. - 2469-9950 .- 2469-9969. ; 108:18
  • Tidskriftsartikel (refereegranskat)abstract
    • Fe-Ga alloys show an unusually large increase in magnetostriction compared to pure Fe and are one of the most interesting Fe-based alloys for this reason. However, the origin of the large magnetostriction and its relation to the chemical ordering on the underlying bcc phase is still under debate. To gain further understanding of the extraordinary magnetoelastic characteristics of this system, we investigate the effect of Ga-concentration and ordering on the spin-wave spectra and stiffness. The magnetic interactions in the Fe-Ga alloys are obtained by ab initio electronic structure calculations and the magnon spectra are modeled using atomistic spin dynamics modeling. Our results agree with available experimental data and show softening of the magnon modes with increasing Ga-concentration and a strong reduction of the spin-wave stiffness due to atomic ordering.
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9.
  • Löfgren, Robin (författare)
  • A Theoretical Investigation of the Nitrogen-Vacancy Center in Diamond as a Single Molecule Sensor and Qubit : Charging through Explicit Electron Donors
  • 2021
  • Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
    • The NV-center in diamond is one of the most well researched defects to date. Since its discovery in the 1960’s, a large body of experimental as well as theoretical work have been produced, investigating its properties and applications. The reason for the attention on this defect are its properties that are well suited for a number of applications. Some of those properties are: 1) photostable at room temperature; 2) long spin coherence time; 3) spin-flipping during the process of optical excitation and decay; 4) Optical readout of spin state. Some of the applications include qubits in quantum computers and sensors for single molecule properties. In order for the NV-center to function well, it is important to decouple its interaction with other defects in the diamond lattice or with the surface of the diamond, that could have a detrimental effect on the NV-center properties. In this work, we theoretically investigate how the NV-center properties are affected by some nearby defects. Those defects include: a nitrogen point defect in the diamond lattice, diamond surfaces, and an extended intrinsic stacking fault defect in the diamond lattice. It is the negative charge state of the NV-center that has the properties mentioned above, and therefore it is this charge state that is interesting for the applications. Here, we investigate our new theoretical method of charging the NV-center through an electron donor nitrogen in the diamond lattice. By instead charging with an explicit electron donor/acceptor, we avoid the complicated correction schemes associated with the tra-ditional theoretical method of introducing an artificial background charge density in a supercell for simulating charged defects. It can also be argued that our new method is a more physically correct method, as negatively charged NV-centers in diamond get their charge by accepting electrons from nearby nitrogens in the diamond lattice. In addition to the NV-center, we further test the method for other point defects in diamond.In this thesis, an introduction to the field is given and the current research questions are stated in chapter 1. Followed by chapters reviewing the current experimental and theoret-ical work regarding the NV-center, computational physics and density functional theory, and an overview of the software used in this work. The results presented in this thesis are obtained using density functional theory computations.Our results show that the method of charging the NV-center with a donor-nitrogen is viable for an NV-N distance of 7.5 ˚A or greater.When placing the NV-center in the vicinity to a terminated surface (F- H/O/OH- and N-terminated), its properties converge to bulk values already at 5 ˚A depth. This is great news when compared with the recent experimentally achieved distance of 1 nm, meaning that NV-centers could possibly be placed even closer to the surface without being affected. When placing the NV-center in the vicinity of an intrinsic stacking fault (ISF), our results show that the NV-center is not greatly affected down to a distance of 4.2 ˚A. However, when the NV-center is placed 3.8 ˚A or closer to the ISF, the ZPL is perturbed between 2.0 and 11.3 %. It is perturbed the most when placed inside the ISF glide plane. This is great news for the technical applications; some diamonds contain high densities of ISFs, and our results show that a NV-center can be placed really close to such an ISF without losing its sensitivity as a sensor of magnetic fields.We have also found that the excitation from the NV− ground state into donor-N+ (one-photon process) requires 2.31 eV and lead to a meta-stable NV0 and donor-N0 charge state, both of which are electron spin resonance (ESR) active and, thus, this transition could be investigated experimentally. The excitation to the neutral state can also be achieved through a two-photon process with the first step at 2.19 eV and the second step at 0.81 eV.When placing the NV-center in the vicinity to two nitrogens (one neutrally charged, and one positively charged acting as electron donor), we find that it is almost unaffected, with changes in the ZPL of 1-8 meV when the distance to the nitrogens is 9.40-12.52 ˚A. This means that a nearby nitrogen, whether it is neutral or positively charged does not affect the NV-center in a detrimental way.Our tests on charging defects through electron donors/acceptors reveals that our method also works for the following defect-donor/acceptor pairs: NV−-P+, NV−-B+, N+-B−, SiV−-N+, Be−-O+, Be2−-N+-N+.
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10.
  • Rodrigues, Debora C. M., et al. (författare)
  • Finite-temperature interatomic exchange and magnon softening in Fe overlayers on Ir(001)
  • 2016
  • Ingår i: Physical Review B. - 2469-9950 .- 2469-9969. ; 94:1
  • Tidskriftsartikel (refereegranskat)abstract
    • We evaluate how thermal effects soften the magnon dispersion in 6 layers of Fe(001) on top of Ir(001). We perform a systematic study considering noncollinear spin arrangement and calculate configuration-dependent exchange parameters J(ij)(nc) following the methodology described by Szilva et al. [Phys. Rev. Lett. 111, 127204 (2013)]. In addition, Monte Carlo simulations were performed in order to estimate the noncollinear spin arrangement as a function of temperature. Hence the J(ij)(nc)'s related to these configurations were calculated and used in an atomistic spin dynamics approach to evaluate the magnon spectra. Our results show good agreement with recent room-temperature measurements, and highlights how thermal effects produce magnon softening in this, and similar, systems
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  • Resultat 1-10 av 24

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