The impact of reduced dimensionality on the magnetic properties of the tetragonal L10 CoPt alloy is investigated from ab-initio considering several kinds of surface defects. By exploring the dependence of the magnetocrystalline anisotropy energy (MAE) on the thickness of CoPt thin films, we demonstrate the crucial role of the chemical nature of the surface. For instance, Pt-terminated thin films exhibit huge MAEs which can be 1000% larger than those of Co-terminated films. Besides the perfect thin films, we scrutinize the effect of defective surfaces such as stacking faults or anti-sites on the surface layers. Both types of defects reduce considerably the MAE with respect to the one obtained for Pt-terminated thin films. A detailed analysis of the electronic structure of the thin films is provided with a careful comparison to the CoPt bulk case. The behavior of the MAEs is then related to the location of the different virtual bound states utilizing second order perturbation theory.
Ferromagnetic L10 ordered alloys are extensively studied nowadays as good candidates for high density magnetic storage media due to their high magnetic anisotropy, related to their chemical order anisotropy. Epitaxial thin bilayers NiPt/FePt/MgO(001) have been grown at 700 K and annealed at 800 K and 900 K. At 800 K, the L10 long-range order increases without measurable interdiffusion. At 900 K, the interdiffusion takes place without destroying the L10 long-range order. This surprising observation can be explained by different diffusion mechanisms that are energetically compared using molecular dynamics simulations in CoPt in the second moment tight binding approximation. In addition, the frequencies of the normal modes of vibration have been measured in FePd, CoPt and FePt single crystals using inelastic neutron scattering. The measurements were performed in the L10 ordered structure at 300 K. From a Born-von Karman fit, we have calculated the phonon densities of states. The migration energies in the 3 systems have been estimated using the model developed by Schober et al. (1981). The phonon densities of states have also been used to calculate several thermodynamic quantities as the vibration entropy and the Debye temperature.
Abstract. We present atomic-scale computer simulations in equiatomic L10-CoPt where Molecular Dynamics and Monte Carlo techniques have both been applied to study the vacancy-atom exchange and kinetics relaxation. The atomic potential is determined using a Tight-Binding formalism within the Second-Moment Approximation. It is used to evaluate the different saddle-point energies involved in a vacancy-atom exchange between nearest-neighbour sites. The potential and the saddle-point energies have been used to simulate the relaxation of the long-range order in CoPt using a Monte Carlo technique. A vacancy migration energy of 0.73 ± 0.15 eV and an order-disorder transition temperature of 935 K have been found.
PACS
We present a first principles investigation of the electronic properties of monolayer WS2 coated with an overlayer of Fe. Our ab initio calculations reveal that the system is a half-metallic ferromagnet with a gap of ∼ 1 eV for the majority spin channel. Furthermore, the combined effect of time-reversal symmetry breaking due to the magnetic Fe overlayer and the large spin-orbit coupling induced by W gives rise to non-degenerate K and K valleys. This has a tremendous impact on the excited state properties induced by externally applied circularly polarized light. Our analysis demonstrates that the latter induces a singular hot spot structure of the transition probability around the K and K valleys for right and left circular polarization, respectively. We trace back the emergence of this remarkable effect to the strong momentum dependent spin-noncollinearity of the valence band involved. As a main consequence, a strong valley-selective magnetic circular dichroism is obtained, making this system a prime candidate for spintronics and photonics applications.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.