Browsing by Author "Sauceda Flores, JA"

Now showing 1 - 5 of 5
  • Thumbnail Image
    Item
    Exploring the novel pyrovanadate series K2Mn1-xCoV2O7
    (Australian Institute of Physics, 2020-02-04) Smith, M; Avdeev, M; Sauceda Flores, JA
    Materials with the Melilite-type structure have been intensively studied throughout the years due to their interesting piezoelectric, electrochemical, luminescent, magnetic, and structural properties [1,2]. Many oxides with the general formula A2BC2O7 crystallise into the melilite family of minerals, where A is a large cation from group one or two; B is typically a first-row transition metal with four-fold coordination; and C is a smaller cation like Si, V, P, or Ge [1-4]. The Pyrovanadate (A2BV2O7) compounds K2MnV2O7 and K2CoV2O7 exist in the melilite group, with the tetragonal space group P4̅21m, consisting of alternating layers of K+ ions in between MV2O72- sheets comprised of connected MO4 and VO4 tetrahedra (Figure 1) [1,2]. The crystal structure K2Mn1-xCoV2O7 was determined from the rietveld refinement of powder X-ray diffraction (PXRD) patterns. Refinement of PXRD patterns showed a systematic shift in reflections with increasing cobalt content, consistent with an increase of lattice constant parameters. UV-Vis measurements show how the addition of cobalt leads to an additional electronic transition whose intensity increases with increasing cobalt concentration. Tauc plots revealed that the material has a direct band gap of approximately 2 eV. Photoluminescent measurements of the cobalt doped species revealed promising results for white light emitters due to electronic transitions across the cobalt tetrahedra and pyrovanadate units. First magnetic measurements indicate a long-range antiferromagnetic ordering at just over 2 K for K2CoV2O7.
  • Thumbnail Image
    Item
    Exploring the pyrophosphate series K2Cu1-xFexP2O7
    (Australian Institute of Physics, 2020-02-04) Silk, R; Avdeev, M; Sauceda Flores, JA; Ulrich, C; Söhnel, T
    Phosphate materials are of great interest to materials science. Metal phosphate compounds are known to exhibit conductive properties for battery use [1], photocatalytic abilities to decompose other compounds [2], the ability to conduct protons [3], etc. High temperature sintering techniques were used to produce the diphosphate series K2Cu1-xFexP2O7. The material forms two different modifications, a tetragonal (P-421m) and an orthorhombic modification (Pbnm) as shown in Figure 1. The crystal structure was determined through the use of powder X-ray diffraction (PXRD). PXRD patterns show a shift in peaks to lower angles with increasing iron content, which is consistent with an increase of lattice constant parameters. The presence of additional phases such as KPO3 can also be observed. UV-Vis measurements show how the transitions change which increasing amounts of iron and different modifications. Tauc plots revealed that the material has a direct band gap of approximately 3 eV. IR measurements revealed that water had been absorbed by the material and there a slight shift in peak position with increasing iron content. First magnetic measurements did not show any long-range ordering down to 2 K, the compounds remained paramagnetic. The K2CuP2O7 and K2Cu0.75Fe0.25P2O7 samples show short-range antiferromagnetic contribution across both modifications.
  • Thumbnail Image
    Item
    Increase of the stability range of the skyrmion phase in doped Cu2OSeO3
    (Australian Institute of Physics, 2020-02-04) Sauceda Flores, JA; Rov, R; Camacho, L; Spasovski, M; Vella, J; Yick, S; Gilbert, EP; Han, MG; Zhu, Y; Seidel, J; Kharkov, Y; Sushkov, OP; Söhnel, T; Ulrich, C
    A skyrmion is a topological stable particle-like object comparable to a spin vortex at the nanometre scale. It consists of an about 50 nm large spin rotation and its spin winding number is quantized. Once formed, the skyrmions order in a two dimensional, typically hexagonal superstructure perpendicular to an applied external magnetic field (see Fig. 1). Its dynamics has links to flux line vortices as in high temperature superconductors. Cu2OSeO3 is a unique case of a multiferroic materials where the skyrmion dynamics could be controlled through the application of an external electric field. The direct control of the skyrmion dynamics through a non-dissipative method would offer technological benefits and unique possibilities for testing fundamental theories also related to the Higgs Boson whose theoretical description has similarities to skyrmions. Important for technological applications is a stability range of the skyrmion phase up to room temperature. While room temperature skyrmion materials exist, Cu2OSeO3 orders magnetically below 58 K. Our combined small angle neutron scattering (see Fig. 2), SQUID magnetization measurements and electron microscopy investigations did provide direct evidence that the stability range of the skyrmion phase can be extended in Te-doped Cu2OSeO3. The understanding of this effect will help to obtain deeper insights in the magnetic correlations in charge of the skyrmion formation and will thus help to systematically search for skyrmion materials with phase transition temperatures towards room temperature.
  • Thumbnail Image
    Item
    Preparation and structural characterisation of pure and Te-doped Cu2OSeO3
    (Australian Institute of Physics, 2020-02-04) Rov, R; Sauceda Flores, JA; Gilbert, EP; Yick, S; Ulrich, C; Söhnel, T
    Cu2OSeO3 is a multiferroic materials that shows the formation of skyrmions at low temperatures. A skyrmion is a topologically protected particle-like magnetic spin structures on the order of 10-100 nm. Recent studies have also shown that the skyrmions can be manipulated through applications such as an external electric fields and heat. This offers the potential for development for a much more stable, energy efficient and faster storage in memory devices. The magnetic skyrmions pack into a hexagonal lattice with the skyrmion lattice only stable in a narrow magnetic field-temperature range [1,2]. Here we present the preparation of pure and Te-doped Cu2OSeO3 single crystals with chemical vapour transport, the structural characterisation with X-ray and neutron single crystal diffraction, small angle neutron scattering and magnetisation measurements. Mapping of the magnetic field-temperature phase diagram showed that tellurium doping resulted in an enlarged stability range for the skyrmion phase had been achieved [3].
  • Thumbnail Image
    Item
    Scaling behaviour of the skyrmion phases of Cu2OSeO3 single crystals from small angle neutron scattering
    (Australian Institute of Nuclear Science and Engineering (AINSE), 2020-11-11) Sauceda Flores, JA; Jorge, A; Rov, R; Pervez, MF; Spasovski, M; O’Brien, J; Vella, J; Seidel, J; Yick, S; Gilbert, EP; Tretiakov, OA; Soehnel, T; Ulrich, C
    A skyrmion is a topological stable particle-like object comparable to a spin vortex at the nanometre scale. It consists of an about 50 nm large spin rotation and its spin winding number is quantised. Skyrmions emerge in chiral crystals as the result of competing symmetric exchange and asymmetric Dzyaloshinskii-Moriya (DM) interactions and typically form two dimensional hexagonal lattices perpendicular to an applied magnetic field. Its dynamics has links to flux line vortices as in high-temperature superconductors [1-2]. Cu2OSeO3 is a unique case of a multiferroic material where the skyrmion dynamics could be controlled through the application of an external electric field. The direct control of the skyrmion dynamics through a non-dissipative method would offer technological benefits applicable in energy-efficient data storage and data processing devices or for testing fundamental theories also related to the Higgs Boson whose theoretical description has similarities to skyrmions [3]. The technological applications crucially depend on the stability conditions of the skyrmion phase up to room temperature. While some materials host skyrmion lattices above room temperature [3], Cu2OSeO3 is the only insulating skyrmion material discovered so far, which orders magnetically below 58 K. It is interesting to note that the appearance of two different skyrmion phases have been reported along the temperature and magnetic field phase diagram of Cu2OSeO3 when the sample is aligned with its main crystallographic axes parallel to the incoming neutron beam and performing Zero Field Cooling (ZFC) or Field Cooling (FC) across the high-temperature skyrmion phase. However, the stabilisation processes of these two phases and their thermodynamic connection are still under debate [4-6]. We have used small angle neutron scattering and Lorentz transmission electron microscopy [7] to study the scaling behaviour of helical phase and the magnetic skyrmion lattices, i.e. the systematic change of their distances in single crystals of Cu2OSeO3 in order to gain insight on the balance between the different competing magnetic exchange interactions. Therefore, we have examined the field, temperature and sample alignment dependence of the scaling behaviour of skyrmions as an order parameter for the emergence of the two aforementioned skyrmion phases. The obtained data provide valuable information on the formation mechanism of the skyrmions and their stability range. This is an important step towards the understanding of the manipulation of skyrmions, which is required for technological applications. © The Authors