Order-disorder phenomena in geometrical frustrated systems are the attractive topics because of the intrinsic fluctuation. Among the geometrical frustrated systems, the material with spinel structure (AB2X4) is one of the appropriate candidates to investigate the long range ordering behavior. Corner sharing of tetrahedron and edge sharing of octahedron in the unique structural network of spinel structure are the characteristics for geometrical frustration. Hence, to study the 3d transition metal substituted in spinel system which leads to fruitful physical behavior becomes rapidly attractive. In this dissertation, long range ordering behavior in spin frustrated systems including three interesting materials LiTi2O4, NaxCoO2¡DyH2O, and CdCr2S4 were investigated. LiTi2O4 was found to show the highest superconducting transition temperature (Tc ~ 11 K) while first hydrated superconductor NaxCoO2¡DyH2O (Tc~ 4.5 K) was discovered in 2003. Superconductivity of LiTi2O4 and NaxCoO2¡DyH2O had been measured and analyzed by low temperature specific heat under magnetic field. According to the analyses of specific-heat results, isotropic (s-wave) and nodal (d-wave) gaps of superconducting pairing symmetry were proposed for LiTi2O4 and NaxCoO2¡DyH2O, respectively. Finally, LiTi2O4 was confirmed to be a typical BCS-like, fully gapped, and electron-phonon moderate-coupling type-II superconductor. Not like the case of LiTi2O4, the superconducting parameters of NaxCoO2¡DyH2O, such as Tc, HC2 and pairing symmetry, were strongly dependent on synthesized conditions. However, the evidence of nodal gap was found to be an intrinsic feature in this peculiar material NaxCoO2¡DyH2O. In the ferromagnetic insulator CdCr2S4, we first found several interesting features induced by external electric field in dielectric and magnetization measurements. Exchangestriction was proposed to be associated with the colossal change of dielectric constant value and suppression of magnetization under external electric and magnetic field in CdCr2S4. Therefore, our results supported that CdCr2S4 was a typical multiferroic material. In a conclusion, the intrinsic fluctuation of spin frustrated systems wasnecessary to pay more attention in the near future due to its fruitful physical properties and behind theoretical description.
| Identifer | oai:union.ndltd.org:NSYSU/oai:NSYSU:etd-0703108-113801 |
| Date | 03 July 2008 |
| Creators | Sun, Chia-pin |
| Contributors | Chin-shan Lue, Hung-duen Yang, Jiunn-yuan Lin, Yung- Kang Kuo, Hsiung Chou |
| Publisher | NSYSU |
| Source Sets | NSYSU Electronic Thesis and Dissertation Archive |
| Language | English |
| Detected Language | English |
| Type | text |
| Format | application/pdf |
| Source | http://etd.lib.nsysu.edu.tw/ETD-db/ETD-search/view_etd?URN=etd-0703108-113801 |
| Rights | unrestricted, Copyright information available at source archive |
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