In the geometrical spin frustrated systems, order-disorder phenomena are interesting, for their intrinsic fluctuation, complicated completing interactions, and lattice structure leading to many intrigue physical behavior. To clarify the mechanism of such systems, experiments under extreme conditions (diverse magnetic fields and hydrostatic pressures) are powerful tools to meet the needs.
In this dissertation, two kind of interesting materials are investigated. One is quasi-1D double chain antiferromagnet NaV2O4, the other is cubic like ferrimagnet Cu2OSeO3. In the polycrystalline compound NaV2O4, it exhibits an antiferromagnetic transition TN at 140 K, together with two field dependence subphases at 1 T≤H≤5 T. The two characteristic temperature TN1 and TN2 are associated to two subphases, which is determined by the peak position in the derivative of magnetization with respect to temperature. Under magnetic field, TN and TN1 remain almost unchanged (linear behavior), while TN2 acts in a nonlinear behavior with the application of magnetic field. Further, TN1 and TN2 are found to decrease roughly linear with applied pressure, while TN2 follows a nonlinear relation with applied pressure. On the other hand, the cubic single crystal Cu2OSeO3 exhibits a ferrimagnetic transition at 58 K, which is shifting to high temperature range with increasing magnetic fields. The peak values (from the mutual inductance measurements) associated with the ferrimagnetic transitions also increase with applied hydrostatic pressures. Moreover, the spin-flipped transitions are observed below transition temperature at ambient and applied pressure (12.67 kbar). The measurements above strongly suggested the ferrimagnetic spin configurations order earlier, i.e. transition temperatures increase with applied magnetic fields and pressures. In summary, the investigated frustrated spin systems (NaV2O4 and Cu2OSeO3) behave with the same trend with applied magnetic fields and hydrostatic pressures. It is possibly induced by the external DC magnetic field and the structure change and/or deformation under pressure.
| Identifer | oai:union.ndltd.org:NSYSU/oai:NSYSU:etd-0730110-163301 |
| Date | 30 July 2010 |
| Creators | Tseng, Kuo-feng |
| Contributors | Jiunn-Yuan Lin, Yung-Sung Chen, Hung-Duen Yang, 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-0730110-163301 |
| Rights | withheld, Copyright information available at source archive |
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