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

为了阐明四方 RB_2C_2 化合物中的反铁四极 (AFQ) 相互作用和有序性，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。磁相图确定为无 DyB_2C_2，AFQ 有序温度为 T_Q=24.3 K，反铁磁（AFM）T_N=l5.3 K和HoB_2C_2之一，具有T_N=5.8 K和T_Q=5.0 K的反向跃迁序列。通过单晶中子衍射也确定了每个相中存在的AFM、AFQ或其共结构此外，还揭示了 AFM TbB_2C_2 的反常相图。 T_N=21.7 K源于场致AFQ有序转变的发生，并且还阐明了其场致相的AFM和AFQ结构。HoB_2C_2中T_Q≤T≤T_N的磁相，其中h与( AFM+AFQ)相与立方体(Ce,La)B_6中的(IV相)有一些相似之处，其特征是神秘且人们还强烈发现，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，其中的转变序列与 HoB_2C_2 中的相同。由于其可能受到八极相互作用强烈影响的神秘特性，已在四种化合物中发现，因此成为该领域未来研究的最重要目标。强中子衍射和 ^<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 相互作用则作用于 C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。