RESUMO
We employ first-principles molecular dynamics simulations to provide equation-of-state data, pair distribution functions (PDFs), diffusion coefficients, and band gaps of a mixture of hydrogen and methane under planetary interior conditions as relevant for Uranus, Neptune, and similar icy exoplanets. We test the linear mixing approximation, which is fulfilled within a few percent for the chosen P-T conditions. Evaluation of the PDFs reveals that methane molecules dissociate into carbon clusters and free hydrogen atoms at temperatures greater than 3000 K. At high temperatures, the clusters are found to be short-lived. Furthermore, we calculate the electrical conductivity from which we derive the non-metal-to-metal transition region of the mixture. We also calculate the electrical conductivity along the P-T profile of Uranus [N. Nettelmann et al., Planet. Space Sci., 2013, 77, 143-151] and observe the transition of the mixture from a molecular to an atomic fluid as a function of the radius of the planet. The density and temperature ranges chosen in our study can be achieved using dynamic shock compression experiments and seek to aid such future experiments. Our work also provides a relevant data set for a better understanding of the interior, evolution, luminosity, and magnetic field of the ice giants in our solar system and beyond.
RESUMO
The observation of in-plane ferromagnetism in layered magnetic materials in conjunction with the topological nodal-ring dispersion in a spin gapless semimetal with 100 % spin polarization has a fertile ground for novel physics, rich scientific significance and for the next-generation advanced spintronic and topological devices. Topological nodal ring spin gapless semimetals with large band gap in the other spin channel prevents the spin leakage and are excellent spintronic materials. On the basis of density functional theory (DFT), we have studied the layered magnetic perovskite, CsMnF4which is predicted to be a ferromagnetic insulator though the fellow compounds likeAMnF4(A= Na, K, Rb) are anti-ferromagnetic in nature. DFT +Ucalculations reveal that this layered system undergoes a transition from an insulating to half-semimetallic nature with decreasing on-site Hubbard Coulomb interaction,U. ForU= 2.5 eV, we observe the topological nature in the system with the emergence of four Mexican hat like dispersions associated with band-flipping. Also, we calculated the magneto-crystalline anisotropic energy with inclusion of spin-orbit coupling (SOC) and found that the system consists of in-plane ferromagnetism. Transport properties infer huge anisotropy of one order of magnitude between 'a' and 'c' axes. Interestingly, the estimated Fermi velocities are 2.66 × 105and 2.24 × 105m s-1forZ(=0) andZ(=0.5) plane respectively and are comparable to that of graphene, which might fetch applications in high speed spin electronic devices. The topological phase observed is robust to SOC and the band-crossings associated with nodal rings could be preserved by additional symmetry as the time-reversal symmetry breaks in magnetic systems. The nearly charge compensation observed from Fermi surfaces might fetch memory device applications.
