Scaling, rotation, and channeling behavior of helical and skyrmion spin textures in thin films of Te-doped Cu2OSeO3.

Topologically nontrivial spin textures such as vortices, skyrmions, and monopoles are promising candidates as information carriers for future quantum information science. Their controlled manipulation including creation and annihilation remains an important challenge toward practical applications and further exploration of their emergent phenomena. Here, we report controlled evolution of the helical and skyrmion phases in thin films of multiferroic Te-doped Cu2OSeO3 as a function of material thickness, dopant, temperature, and magnetic field using in situ Lorentz phase microscopy. We report two previously unknown phenomena in chiral spin textures in multiferroic Cu2OSeO3: anisotropic scaling and channeling with a fixed-Q state. The skyrmion channeling effectively suppresses the recently reported second skyrmion phase formation at low temperature. Our study provides a viable way toward controlled manipulation of skyrmion lattices, envisaging chirality-controlled skyrmion flow circuits and enabling precise measurement of emergent electromagnetic induction and topological Hall effects in skyrmion lattices.

Synthesis, structure and geometrically frustrated magnetism of the layered oxide-stannide compounds Fe(Fe3-xMnx)Si2Sn7O16.

Fe4Si2Sn7O16 has a unique crystal structure that contains alternating layers of Fe(2+) ions octahedrally coordinated by O (oxide layer) and Sn (stannide layer), bridged by SiO4 tetrahedra. The formula can be written as FeFe3Si2Sn7O16 to emphasise the distinction between the layers. Here, we report the changes in structure and properties as iron is selectively replaced by manganese in the oxide layer. Solid-state synthesis was used to produce polycrystalline samples of Fe(Fe3-xMnx)Si2Sn7O16 for x≤ 2.55, the structures of which were characterised using high-resolution synchrotron X-ray and neutron powder diffraction. Single-crystal samples were also grown at x = 0.35, 0.95, 2.60 and characterised by single crystal X-ray diffraction. We show that manganese is doped exclusively into the oxide layer, and that this layer contains exclusively magnetically active high-spin M(2+) transition metal cations; while the stannide layer only accommodates non-magnetic low-spin Fe(2+). All samples show clear evidence of geometrically frustrated magnetism, which we associate with the fact that the topology of the high-spin M(2+) ions in the oxide layer describes a perfect kagomé lattice. Despite this frustration, the x = 0 and x = 2.55 samples undergo long-range antiferromagnetic ordering transitions at 3.0 K and 2.5 K, respectively.

A DFT + U computational study on stoichiometric and oxygen deficient M-CeO2 systems (M = Pd1, Rh1, Rh10, Pd10 and Rh4Pd6).

Molecular and dissociative adsorption processes of ethanol on stoichiometric and O-defected CeO2(111) surfaces alone as well as in the presence of one metal atom (Pd or Rh) are studied using spin-polarized density functional theory (DFT) with the GGA + U method (Ueff = 5.0 eV). Dissociative adsorption (onto ethoxides) is slightly more stable than molecular adsorption onto stoichiometric CeO2(111). The creation of surface oxygen vacancies further stabilizes both modes. In the case of ethoxide adsorbed onto a Ce(3+) cation, adjacent to the oxygen vacancy, charge transfer to a nearest Ce(4+) cation occurs. In addition, the interactions of Pd1 (or Rh1), Pd10 (or Rh10) as well as of a bimetal cluster (Rh4Pd6) with perfect and O-defected CeO2(111) surfaces have been studied. From spin density calculations, it was found that the addition of metal changes the oxidation state of Ce(4+) cations. The magnetic moment at the neighboring Rh or Pd induces a charge transfer to Ce(4+) cations (i.e. Ce(4+) (4f(0)) that becomes Ce(3+) (4f(1))) and consequently M is oxidized to Pd(δ+) (or Rh(δ+)). Similar to the atomic metal adsorption, Rh10 has a stronger adsorption energy on the perfect surface than Pd10 (Eads = -6.49 and -5.75 eV, respectively), while that of Rh4Pd6 was in between (Eads = -6.00 eV). The effect of one metal atom on the adsorption of ethanol was also studied. The presence of the metal further stabilized the adsorption energy of ethanol/ethoxide in its bridging configuration. The creation of an oxygen vacancy nearest the metal resulted in considerable stabilization of ethoxides (Eads = -1.67 eV in the case of Pd) compared to those found on the O-defected CeO2(111) surface alone (Eads = -0.85 eV).

Phase stabilities at a glance: stability diagrams of nickel dipnictides.

In the course of the recent advances in chemical structure prediction, a straightforward type of diagram to evaluate phase stabilities is presented based on an expedient example. Crystal structures and energetic stabilities of dipnictides NiPn2 (Pn = N, P, As, Sb, Bi) are systematically investigated by first principles calculations within the framework of density functional theory using the generalized gradient approximation to treat exchange and correlation. These dipnictides show remarkable polymorphism that is not yet understood systematically and offers room for the discovery of new phases. Relationships between the concerned structures including the marcasite, the pyrite, the arsenopyrite/CoSb2, and the NiAs2 types are highlighted by means of common structural fragments. Electronic stabilities of experimentally known and related AB2 structure types are presented graphically in so-called stability diagrams. Additionally, competing binary phases are taken into consideration in the diagrams to evaluate the stabilities of the title compounds with respect to decomposition. The main purpose of the stability diagrams is the introduction of an image that enables the estimation of phase stabilities at a single glance. Beyond that, some of the energetically favored structure types can be identified as potential new phases.

The stability of gold iodides in the gas phase and the solid state.

The stability of gold iodides in the oxidation state +I and +III is investigated at the ab initio and density functional level using relativistic and nonrelativistic energy-adjusted pseudopotentials for gold and iodine. The calculations reveal that relativistic effects stabilize the higher oxidation state of gold as expected, that is Au2I6 is thermodynamically stable at the relativistic level, whilst at the nonrelativistic level the complex of two iodine molecules weakly bound to both gold atoms in Au2I2 is energetically preferred. The rather low stability of AuI3 with respect to dissociation into AuI and I2 will make it difficult to isolate this species in the solid state as (possibly) Au2I6 or detect it by matrix-isolation techniques. The monomer AuI3 is Jahn-Teller distorted from the ideal trigonal planar (D3h) form, but adopts a Y-shaped structure (in contrast to AuF3 and AuCl3), and in the nonrelativistic case can be described as I2 weakly bound to AuI. Relativistic effects turn AuI3 from a static Jahn-Teller system to a dynamic one. For the yet undetected gas-phase species AuI accurate coupled-cluster calculations for the potential energy curve are used to predict vibrational-rotational constants. Solid-state density functional calculations are performed for AuI and Au2I6 in order to predict cohesive energies.

Nuclear quadrupole moment of 57Fe from microscopic nuclear and atomic calculations.

The nuclear quadrupole moment (NQM) of the Ipi = 3/2(-) excited nuclear state of 57Fe at 14.41 keV, important in Mössbauer spectroscopy, is determined from the large-scale nuclear shell-model calculations for 54Fe, 57Fe, and also from the electronic ab initio and density functional theory calculations including solid state and electron correlation effects for the molecules Fe(CO)(5) and Fe(C5H5)(2). Both independent methods yield very similar results. The recommended value is 0.15(2) e b. The NQM of the isomeric 10+ in 54Fe has also been calculated. The new NQM values for 54Fe and 57Fe are consistent with the perturbed angular distribution data.