Magnetism of Gadolinium: A First-Principles Perspective

By calculating the spectral density of states in the ferromagnetic ground state and in the high temperature paramagnetic phase we provide the first concise study of finite temperature effects on the electronic structure of the bulk and the surface of gadolinium metal. The variation of calculated spectral properties of the Fermi surface and the density of states in the bulk and at the surface are in good agreement with recent photoemission experiments performed in both ferromagnetic and paramagnetic phases. In the paramagnetic state we find vanishing spin splitting of the conduction band, but finite local spin moments both in bulk and at the surface. We clearly demonstrate that the formation of these local spin moments in the conduction band is due to the asymmetry of the density of states in the two spin channels, suggesting a complex, non-Stoner behavior. We, therefore, suggest that the vanishing or nearly vanishing spin splitting of spectral features cannot be used as an indicator for Stoner-like magnetism. © 2015 American Physical Society

Osmates on the Verge of a Hund's-Mott Transition: The Different Fates of NaOsO3 and LiOsO3

We clarify the origin of the strikingly different spectroscopic properties of the chemically similar compounds NaOsO3 and LiOsO3. Our first-principle, many-body analysis demonstrates that the highly sensitive physics of these two materials is controlled by their proximity to an adjacent Hund's-Mott insulating phase. Although 5d oxides are mildly correlated, we show that the cooperative action of intraorbital repulsion and Hund's exchange becomes the dominant physical mechanism in these materials if their t2g shell is half filled. Small material specific details hence result in an extremely sharp change of the electronic mobility, explaining the surprisingly different properties of the paramagnetic high-temperature phases of the two compounds

Temperature-dependent exchange stiffness and domain wall width in Co

The micromagnetic exchange stiffness is a critical parameter in numerical modeling of magnetization dynamics and reversal processes, yet the current literature reports a wide range of values even for such simple and widely used material as cobalt. Using the ab initio estimated Heisenberg parameters we calculate the low temperature micromagnetic exchange stiffness for hexagonal-close-packed (hcp) and face-centered-cubic cobalt. For hcp Co they are slightly different in the directions parallel and perpendicular to the c axis. We establish the exchange stiffness scaling relation with magnetization A(m)∼m1.8 valid for a wide range of temperatures. For hcp Co we find an anisotropic domain wall width in the range 24-29 nm which increases with temperature. The results form a critical input for large-scale temperature-dependent micromagnetics simulations and demonstrate the importance of correct parametrization for accurate simulation of magnetization dynamics

Magnetic behavior of nanocrystalline ErCo2

We have investigated the magnetic behavior of the nanocrystalline form of a well-known Laves phase compound, ErCo2 - the bulk form of which has been known to undergo an interesting first-order ferrimagnetic ordering near 32 K - synthesized by high-energy ball-milling. It is found that, in these nanocrystallites, Co exhibits ferromagnetic order at room temperature as inferred from the magnetization data. However, the magnetic transition temperature for Er sublattice remains essentially unaffected as though the (Er)4f-Co(3d) coupling is weak on Er magnetism. The net magnetic moment as measured at high fields, sat at 120 kOe, is significantly reduced with respect to that for the bulk in the ferrimagnetically ordered state and possible reasons are outlined. We have also compared the magnetocaloric behavior for the bulk and the nano particles.Comment: JPCM, in pres

Nature of the magnetic moment of cobalt in ordered FeCo alloy

The magnets are typically classified into Stoner and Heisenberg type, depending on the itinerant or localized nature of the constituent magnetic moments. In this work, we investigate theoretically the behaviour of the magnetic moments of iron and cobalt in their B2-ordered alloy. The results based on local spin density approximation for the density functional theory (DFT) suggest that the Co magnetic moment strongly depends on the directions of the surrounding magnetic moments, which usually indicates the Stoner-type mechanism of magnetism. This is consistent with the disordered local moment picture of the paramagnetic state, where the magnetic moment of cobalt gets substantially suppressed. We argue that this is due to the lack of strong on-site electron correlations, which we take into account by employing a combination of DFT and dynamical mean-field theory (DMFT). Within LDA + DMFT, we find a substantial quasiparticle mass renormalization and a non Fermi-liquid behaviour of Fe-3d orbitals. The resulting spectral functions are in very good agreement with measured spin-resolved photoemission spectra. Our results suggest that local correlations play an essential role in stabilizing a robust local moment on Co in the absence of magnetic order at high temperatures. © 2021 IOP Publishing Ltd Printed in the UKAG acknowledges AI Poteryaev and AS Belozerov for fruitful discussions, EUSpec COST Action and the Competitiveness Enhancement Programme-CEP 3.1.1.2.?-17. The work is supported by the Swedish Research Council (VR) under the projects 2015-05020 and 2019-03569 as well as Swedish Foundation for International Cooperation in Research and Higher Education (STINT), Project No. IB2018-7490. The computer simulations are performed on computational resources provided by NSC allocated by the Swedish National Infrastructure for Computing (SNIC)