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Competitive Antiferroquadrupolar and Antiferromagnetic Interactions in Tetragonal Rare-earth Compounds RB_2C_2.

四方稀土化合物RB_2C_2中的竞争性反铁四极和反铁磁相互作用。

基本信息

批准号：
12304017
负责人：
YAMAGUCHI Yasuo
金额：
$ 29.36万
依托单位：
Tohoku University
依托单位国家：
日本
项目类别：
Grant-in-Aid for Scientific Research (A)
财政年份：
2000
资助国家：
日本
起止时间：
2000 至 2002
项目状态：
已结题

项目摘要

Growth of single crystals, identification of crystal structure and various measurements such an magnetic susceptibility, magnetization, specific heat, electric resistivity, Mossbauer effect and neutron scattering have been performed is order to clarify antiferroquadrupolar (AFQ) interaction and ordering in tetragonal RB_2C_2 compounds.Precise magnetic phase diagrams were determined no DyB_2C_2 with an AFQ ordering temperature of T_Q=24.3 K and an antiferromagnetic (AFM) one of T_N=l5.3 K and HoB_2C_2 with the reverse transition sequence of T_N=5.8 K and T_Q=5.0 K. The AFM, AFQ or their coexistent structure in every phase was also determined by neutron diffraction on single crystals in magnetic fields. Moreover, it was revealed that anomalous phase diagrams of the AFM TbB_2C_2 with T_N=21.7 K originates in occurrence of field-induced AFQ ordering transitions, and the AFM and AFQ structures of their field-induced phases were also clarified.The magnetic phase of T_Q≦T≦T_N in HoB_2C_2 whic … More h is adjacent to (AFM+AFQ) phase has some resemblance to that (phase IV) in cubic (Ce,La)B_6 that the character has been mysterious and controversial. It has been also found that the AFM phase of TbB_2C_2 is very similar to phase IV in the both compounds and that phase IV appears in (Dy,Gd)B_2C_2 where the transition sequence is the same to that in HoB_2C_2. Phase IV strongly attract us and is the most important target in future research in this field because of its mysterious character which might be affected strongly by octupolar interactions. Phase IV has been found in four compounds, and we found three of them in the RB_2C_2 compounds.Combination of neutron diffraction and ^<161>Dy Mossbauer experiments gave the important information that the strong AFQ interaction mediates along the tetragonal c-axis like a pseude-one-dimmensional interaction while the AEM interactions act strongly in the C-plane. The competition of these AFQ and AFM interactions causes various and anomalous magnetic properties in RB_2C_2. Less

进行了单晶的生长、晶体结构的鉴定以及磁化率、磁化强度、比热、电阻率、穆斯堡尔效应和中子散射等各种测量，以阐明四方 RB_2C_2 化合物中的反铁四极 (AFQ) 相互作用和有序性。在 AFQ 有序温度为 T_Q = 24.3 K和T_N = 15.3 K和HoB_2C_2之一的反铁磁（AFM），具有T_N = 5.8 K和T_Q = 5.0 K的反向跃迁序列。还通过磁场中单晶的中子衍射确定了每个相中的AFM，AFQ或它们的共存结构。此外，还揭示了T_N=21.7 K的AFM TbB_2C_2的反常相图源于场致AFQ有序转变的发生，并阐明了其场致相的AFM和AFQ结构。HoB_2C_2中T_Q≤T≤T_N的磁相与(AFM+AFQ)相相邻。与立方体(Ce,La)B_6中的(第四相)有一些相似之处，该性质一直是神秘且有争议的。还发现TbB_2C_2的AFM相与两种化合物中的IV相非常相似，并且IV相出现在(Dy,Gd)B_2C_2中，其中转变序列与HoB_2C_2中的相同。第四相强烈地吸引了我们，并且是该领域未来研究中最重要的目标，因为它的神秘特性可能会受到八极相互作用的强烈影响。在四种化合物中发现了第四相，我们在RB_2C_2化合物中发现了其中三种。中子衍射和^<161>Dy Mossbauer实验的结合给出了重要信息：强AFQ相互作用沿着四方c轴介导，就像伪一维相互作用，而AEM相互作用在C平面上强烈作用。这些 AFQ 和 AFM 相互作用的竞争导致 RB_2C_2 中出现各种异常的磁特性。较少的