Abstract:
Copper oxides have generated huge interest ever since the discovery of superconductivity in complex materials such yttrium barium copper oxides. Recently it was discovered that the ternary copper oxide Cu₂OSeO₃ is capable of hosting skyrmions, a rare skyrmion host material as most skyrmions system are metallic. A skyrmion is a topological stable particle-like object with the spin ordered in a vortex like fashion on the order of 10-50 nm. The skyrmion lattice is stable in a narrow temperature and magnetic field range, forming a narrow pocket in the magnetic field-temperature phase diagram. Cu2OSeO3 is a magnetoelectric compound thus the individual skyrmions could be controlled through the application of an external electric field. The use of Cu₂OSeO₃ in memory devices offers the potential for stable, more energy efficient and much quicker storage and retrieval of information than currently used. Herein we present the synthesis and characterisation of Te-doped Cu₂OSeO₃ using a variety of techniques. Polycrystalline and single crystal samples of Te-doped Cu₂OSeO₃ were prepared by sintering and chemical vapour transport. Powdered Te-doped Cu₂OSeO₃ produced were not of high quality as shown by powder X-ray diffraction. High quality single crystals of Te-doped Cu₂OSeO₃ were successfully synthesised by chemical vapour transport, with crystals of up to 3 mm3 in size produced. A structural study was completed using single crystal X-ray diffraction providing information on the effects of Te doping and temperature on the crystal structure. The use of electron dispersive spectroscopy and single crystal X-ray diffraction was used to confirm that Te was successfully doped into the Cu₂OSeO₃ structure. The magnetic field-temperature phase diagrams for the bulk Cu₂OSeO₃ and Te-doped Cu₂OSeO₃ single crystals was mapped using small angle neutron scattering. Mapping of the Te-doped Cu₂OSeO₃ showed that there was an enlarged stability range for the skyrmion phase in both temperature and magnetic field.