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Studies on the mechanism of the evolution of multiferroicity for the practical application

多铁性演化机制研究及其实际应用

基本信息

批准号：
17360321
负责人：
ITOH Mitsuru
金额：
$ 9.92万
依托单位：
Tokyo Institute of Technology
依托单位国家：
日本
项目类别：
Grant-in-Aid for Scientific Research (B)
财政年份：
2005
资助国家：
日本
起止时间：
2005 至 2006
项目状态：
已结题

项目摘要

This project has aimed at developing new multiferroics which can be used above room temperature. First target materials were ferroelectric cubic-BaTiO_3 (c-BTO) and hexagonal-BaTiO_3 (h-BTO). Single crystals of these materials were successfully grown by the conventional type floating zone furnace. The size of grown crystals was typically 5 mm in diameter and 50 mm in length. This is the first demonstration that such large sized crystals were obtained for h-BTO and c-BTO. Tuning the growth conditions including growth rate, growing speed, and atmosphere during the growth, we could also obtain the Fe-doped crystal with almost the same size with the pristine composition.Magnetic and dielectric measurements were carried out for the obtained single crystals, c-BTO-Fe showed a ferromagnetism and a ferroelectricity at room temperature. Careful analysis for M-H loop at various temperatures, Fe ion can take the mixed valence state of Fe_<3+> and Fe_<4+>. Heat capacity measurement revealed that F … More e_<3+> and Fe_<4+> ions take high spin and low spin state, respectively. However, the origin of the evolution of the ferromagnetism is not clear at the present time. On the contrary, h-BaTiO_3-Fe system gave consistent results. Fe_<3+> and Fe_<4+> ions take high spin state in Ti l site and low spin state in Ti2 site, respectively. Ferromagnetism originates from Fe_<4+> ions in Ti2 sites in the face-shared octahedral which adjoin each other, and other Fe_<3+> ion in Ti l site act as an isolated spin. Detailed measurements on M-H loop, magnetic susceptibility, and low temperature heat capacity revealed that ferromagnetism is coming from the paired Fe_<4+> ions in the low spin state. These results may give a hint to consider the mechanism of the evolution of ferromagnetism in c-BTO. Even in c-BTO, Fe ion tends to take mixed valence state of Fe_<3+> and Fe_<4+>. The crystal field may render the Fe_<4+> ions to take the low spin state even in the cubic phase. These results will serve as the complete understanding for so-called dilute magnet system, for which single crystal can not be obtained. The discovery of the real multeferroic crystal c-BTO will enhance the comprehensive understanding this field. Less

该项目旨在开发可在室温以上使用的新型多铁性材料。第一种靶材料是铁电性的立方BaTiO_3（c-BTO）和六方BaTiO_3（h-BTO）。用常规型浮区炉成功地生长了这些材料的单晶。生长的晶体的尺寸通常为直径5 mm和长度50 mm。这是首次证明h-BTO和c-BTO获得了如此大尺寸的晶体。通过调节生长速率、生长速度和生长气氛等生长条件，我们也可以得到与原始成分几乎相同尺寸的掺铁晶体，对所得单晶进行了磁性和介电性能的测量，c-BTO-Fe在室温下表现出铁磁性和铁电性。仔细分析不同温度下的M-H环，Fe离子可以以Fe_（3+）和Fe_（4+）的混合价态存在。热容测量表明，F ...更多信息 e3+和Fe 4+分别处于高自旋和低自旋态。然而，铁磁性演化的起源目前尚不清楚。相反，h-BaTiO_3-Fe体系则得到了一致的结果。Fe_（3+）和Fe_（4+）离子分别在Ti_1位和Ti_2位处于高自旋态。铁磁性来源于共面八面体中Ti 2位上的Fe_（4+）离子相互邻接，而Ti 1位上的其它Fe_（3+）离子作为孤立自旋。对M-H环、磁化率和低温热容的详细测量表明，铁磁性来自低自旋态的成对Fe <4+>离子。这些结果可能为探讨c-BTO铁磁性的演化机制提供了线索。即使在c-BTO中，Fe离子也倾向于以Fe_（3+）和Fe_（4+）混合价态存在。晶场的作用使Fe_（4+）离子在立方相中也能处于低自旋态。这些结果将作为对所谓的稀磁系统的完整理解，因为对于稀磁系统，不能获得单晶。真实的多铁性晶体c-BTO的发现将加深对这一领域的全面认识。少