Design and Fabrication of a Miniature AC -Susceptibility Coil-Set Compatible for a Close-Cycle Refrigerator(CCR)

Abstract

In this work, a coil set for ac susceptibility measurement was designed and fabri cated, which is compatible with a Close-Cycle Refrigerator. This coil system consists of one primary coil and two secondary coils wound on a sapphire tube. The pur pose of this miniature coil set is to assess the feasibility of detecting magnetic phase transitions at cryogenic temperatures, particularly below 77K, with a focus on weak antiferromagnetic transitions. This thesis also presents a literature survey on Kitaev candidates such as RuCl3 and Na2IrO3. Chapter 1 of the thesis introduces magnetic materials, including paramagnets, fer romagnets, and antiferromagnets. Chapter 2 details the experimental methods related to this project, including the working of CCR and the principles of ac susceptibility. Chapter 3 presents a short literature survey on quantum spin liquids and Kitaev mag nets such as RuCl3 and Na2IrO3. Chapter 4 presents design and fabrication details of the miniature coil set-up, wound on a sapphire tube during the course of this project. The sapphire tube was attached to a Cu flange that could be fitted and thermally anchored to the cold finger of CCR. Chapter 4 also presents room temperature data on the o!set signal of secondary coils, with and without the copper flange. Chapter 5presentso!setdataasafunctionof temperaturewhentheminiaturecoil setwas fitted inside the CCR. Results of test runs on RuCl3 single crystal as well as ferro magnetic Ni samples are presented in this chapter. Overall, these data indicate that it is di”cult to detect antiferromagnetic transitions using this miniature coil setup in the presence of a huge background signal. Detection of a ferromagnetic signal can be a possibility. However, even for tracking the ferromagnetic transitions, more experi ments are needed to understand the origin of the background signal and its frequency dependence.