High Magnetic Field Study Of Quasi-two-dimensional Oxide Ni₃V₂O₈ And KMo₆O₁₇

In recent years, low dimensional strongly correlated systems have attracted great interest, due to its phenomena of various orders. Frustrated magnet is one kind of this systems. In frustrated magnets, the magnetic interactions cannot be satisfied simultaneously, which causes the degenerate quantum ground-state properties and rich magnetic-phase-transition behaviors. This phenomenon is only observed in sufficient magnetic fields. With respect to this reason, pulsed high magnetic field becomes one of the most powerful tools to study this macroscopic quantum effect. In this paper, we will focus our interests on quasi two-dimensional frustrated magnet Ni3V2O8 and quasi two-dimensional strongly correlated systems KMo6O17. Various pulsed field techniques will be employed to study the magnetic-phase-transition behaviors in that two systems. Research achievements are summarized as following:1.Optical floating zone method is used to grow a large size and high quality single crystal of two-dimensional frustrated magnet Ni3V2O8. Anisotropy in the basic magnetic measurement of the single crystal have shown that it high quality, the magnetic properties are consistent with literature reports. We had magnetic experiments in different temperature and magnetic field?H<12T? systematically, then discovered new phase boundary, which uncovers the H- T magnetic phase diagram when H//a in low magnetic field.2. With pulsed magnetic field up to 60 T, we had research the field induced phase transition of Ni3V2O8 systematically. When the magnetic field parallel to a axis, it is showing continuous magnetic phase transitions induced by field and a fractional magnetization plateau. We studied these properties in different temperature and magnetic pulse width. When the magnetic field parallel to b axis, we constructed the complex H-T phase diagram by the first time by magnetization and specific heat measurement in high magnetic field. And we observed many new magnetic ordered phase. Our findings can help understanding the complex magnetic interactions and frustrations of Ni3V2O8.3. We studied the quantum transport properties of KMo₆O₁₇in high magnetic field. We observed field induced phase transition caused by Pauli effect and orbital effect, the quantum oscillation in high magnetic field uncovers the Fermi surface in low temperature. In addition, we also studid electrical transport properties of KMo₆O₁₇in different angle. And we found phase change showed different characteristic of normalization in two angle range. We believe that the formation of the two different angle range may be associated with the origin of the phase transitions differently.