The Effects of Non-Magnetic and Magnetic Doping on the Skyrmion Hosting Material, Cu2OSeO3
In today’s technological world, the need to store vast amounts of data is increasing at an incredible pace, and with the need forecasted to outgrow the maximum capacity of traditional Si-based electronics, alternative data storage devices are required. The field of spintronics is an emerging field for the next generation of data storage devices with reduced power consumption, increased data density and processing capacities. The material system, Cu2OSeO3, is an attractive material as it is the only insulating multiferroic that hosts magnetic skyrmions, which have been hypothesised as an alternative method to store data. These skyrmions arise from competing Heisenberg exchange and Dzyaloshinskii-Moriya interactions due to the non-centrosymmetric arrangement of the material’s crystal structure. These interactions are mediated through the distance between four magnetic Cu2+ sites, which arrange in ferrimagnetic units. These interactions can be influenced through non-magnetic Te-doping and magnetic Co-doping, which both change the distances between Cu sites. The main goal of this thesis is to investigate the effects of Te and Co-doping on both the crystal structure and magnetic orderings in Cu2OSeO3. The use of synchrotron powder X-ray diffraction and neutron powder diffraction confirmed the successful doping, through the expansion of the unit cell. Both dopants showed a preference to be doped into their respective Se2 and Cu2 sites. Minimal distortions were observed in the bond lengths or angles in the crystal structure; however, minute changes to the interspatial distance between neighbouring Cu2+ sites were noticed to change with doping. Subsequent magnetisation measurements for both dopants observed a lowering of the critical temperatures for the known magnetic phase transitions under zero field, and the expansion of the temperature stability of the skyrmion pocket, along with a shift to lower temperatures. These effects were backed up using small-angle neutron scattering, which was able to observe characteristic magnetic scattering patterns at specific temperatures and magnetic fields to confirm the type of magnetic phase transitions occurring in the magnetometry measurements. With Co-doping, a new magnetic ordering was observed in both the magnetisation data and with a new magnetic scattering pattern that has not been previously reported in polycrystalline samples.
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