Investigation of thermal conductivity and magnetic properties of lacunar spinels GaV4S8 and GaV4Se8
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Kemian tekniikan korkeakoulu |
Master's thesis
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Authors
Date
2024-06-11
Department
Major/Subject
Functional Materials
Mcode
CHEM3025
Degree programme
Master's Programme in Chemical, Biochemical and Materials Engineering
Language
en
Pages
60
Series
Abstract
The interconnection between electricity and magnetism is widely recognized, yet these phenomena are typically studied separately within materials. The discovery of spin-induced ferroelectricity with a strong coupling between magnetism and electric polarization has sig- nificantly boosted the progress combining ferroelectricity and magnetism in the same material. One of these families of materials which has both ferroelectricity and magnetism combined, is lacunar spinels. Two materials from this family of materials, GaV4S8, and GaV4Se8 are investigated due to their intriguing properties such as being ferromagnetic semiconductors that can act as a host for skyrmions. In this thesis the reader will find the basic knowledge of lacunar spinels as a group of materials and learns why they can act as a host to skyrmions. The reader is also introduced to skyrmions. A closer look on the investigated materials, GaV4S8, and GaV4Se8 has been taken. The characterization methods used in this work with reference results are discussed. The reader is also introduced to thermal Hall effect, how it can be utilized to detect charge-neutral excitations, and how the thermal transfer measurement is done. Finally, different thermal Hall effects (THE), such as phonon THE, skyrmion THE, and magnon THE are discussed. In this work, polycrystalline GaV4S8, and GaV4Se8 were synthesized, and their electrical, thermal, and magnetic properties were investigated. It was observed that magnons contribute in GaV4S8’s thermal conductivity. Similarities between GaV4S8’s and GaV4Se8’s thermal conductivity was also observed. It was confirmed that GaV4Se8 has a significantly smaller magnetization than GaV4S8. It was also safely concluded that GaV4Se8 has a positive Seebeck coefficient. In this work a novel method of growing an adequate size GaV4S8 single crystals was reported. This novel synthesis method could lead a path for more effortless synthesis of big GaV4S8 single crystals which can be then used in thermal Hall measurement.Description
Supervisor
Karppinen, MaaritThesis advisor
Tewari, GirishKeywords
lacunar spinels, GaV4S8, GaV4Se8, thermal conductivity, magnetism, CVT