Broadband electrodynamic measurement techniques for multiferroics with applications to BiFeO3 crystals
zspfj 添加于 2010-10-28 12:03
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作 者
J Lu 摘 要
Multiferroics mean those crystals which simultaneously possess memorizable spontaneous charge orderring and memorizable spontaneous spin orderring. Multiferroic materials usually strongly interact with external electrical field, magnetic field or electromagnetic waves et al., so that they may emerge new interesting physical phenomena and promise a bright future for applications. Therefore, undoubtably multiferroics has become one of the hottest topics in the condensed matter physics community. On the other hand, during the overwhelming development of multiferroics, one frequently reads various experimental results which are unfortunately not consistent to each other. Most multiferroic experimental results, taking ferroelectric hysteresis, magnetic hysteresis, dielectric spectrum, permeability spectrum, magnetoelectric spectrum, optical properties et al. for example, have been coming from electrodynamic measurement in particular temperature and frequency windows. To get significant multiferroic experimental results, convincing electrodynamic measurement methods need to be established, as well as using high quality samples. This work was also motivated to help understanding new multiferroic experimental results.
This work has described detailed methods of quality multiferroic measurement for DC experiments and AC measurement techniques from 1 mHz to 1k THz with 18 decades, as well as evaluation methods. This work also invesigates phase equilibra knowledge of BiFeO3 using high purity starting materials (>99.999 wt.%) and improved Bi2O3-Fe2O3 phase diagram. Based on measurement techniques and high-quility BiFeO3 crystals, this work has found some new results for BiFeO3 mainly summarized as follows:
1) The antiferromagnetic phase transition is close to 635 K. No additional magnetic transitions such as spin reorientation or glass behaviours have been found between 2 and 800 K.
2) The intrinsic room-temperature dielectric constant is about 54, along pseudo-cubic c axis and with measurement frequency around 120 GHz.-
详细资料
- 文献种类:学位论文
- 期卷页: 2010年
- 日期: 2010-6-23
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