Browsing by Author "Yick, S"

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    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.
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    Neutron study of magnetic phase transition in SrCoO3 thin films
    (Australian Institute of Physics, 2020-02-04) Yick, S; Peroz, MF; Nagarajan, V; Klose, F; Seidel, J; Ulrich, C
    Transition metal oxides represent a wide set of materials with a broad range of functionalities which can be tuned by the careful choice of parameters such as strain, oxygen content, and applied electric or magnetic fields. When the material exhibits more than one primary ferroic ordering- ferromagnetism, ferroelectricity, ferroelasticity or ferrotoridicity in the same phase, it becomes multiferroic. Such class of materials are of immense technological interest as magnetic and electric transitions can be driven through external factors. This opens new avenues for fundamental research and technical applications in spintronic or magnonic devices. Here, we present results we obtained from neutron-based techniques to investigate the magnetic properties of SrCoO3 and similar thin films. SrCoO3 provides a particularly interesting system for these investigations. Lee and Rabe have simulated the effect of strain and have predicted that the magnetic state can be tuned through compressive or tensile strain with a ferromagnetic-antiferromagnetic phase transition [1,2]. Such a phase transition would be accompanied by a metal-to-insulator phase transition and a transition to a ferroelectric polarized state. By using different substrates, we investigated the effect different epitaxial strain has on SrCoO3 thin films. Previously, our neutron diffraction experiments on these 40 nm thin films have confirmed the predicted but hitherto unobserved phase transition from ferromagnetism to G-type antiferromagnetism when the film was grown on SrTiO3 and DyScO3 substrate respectively [3]. As such, SrCoO3 would constitute a new class of multiferroic material where magnetic and electric polarizations can be driven through external strain. This tunability makes them ideal candidate materials for use in developing novel information and energy technologies.
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    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].
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    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