| Summary: | 碩士 === 國立中山大學 === 物理學系研究所 === 96 === Multiferroic materials, showing strong coupling between ferroelectric and ferromagnetic interaction, have been the subject of intense research recently. These materials are potential candidates for the next generation in microelectronic device. CdCr2S4, one of the few multiferroics with spinel structure proposed in 2005, is in the limelight of scientific research, because of the complex interaction among lattice, spin and dipole. To investigate further, we have measured the magnetic and electric properties of single crystal CdCr2S4. The spins are coupled ferromagnetically below Curie temperature TC = 84 K. With increasing magnetic field, ferromagnetic transition is found to be shifted towards higher temperature. The magnetic hysteresis is satisfied with the characteristic of soft ferromagnet. Electric field induced permanent metal-insulator transition (MIT) and colossal magnetoresistance (CMR) are observed in the resistivity measurement. From dielectric constant measurement, two interesting dipolar ordering states have been observed. The peak near TC ~ 84 K is due to the glassy type dipolar state stimulated by the onset of ferromagnetic ordering and the other near 54 K, might be the ferroelectric ordered state induced by externally applied electric field. Both electric and magnetic field dependent physical properties have been studied and reveal significant evidences of strong spin-dipole coupling in the present system.
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