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Magnetic Ordering and Nonlinear Response of Complex Systems Related to C_<60>

C_<60>相关复杂系统的磁序和非线性响应

基本信息

批准号：
07640513
负责人：
HAGIWARA Makoto
金额：
$ 1.41万
依托单位：
Kyoto Institute of Technology
依托单位国家：
日本
项目类别：
Grant-in-Aid for Scientific Research (C)
财政年份：
1995
资助国家：
日本
起止时间：
1995 至 1997
项目状态：
已结题

项目摘要

Several kinds of complex magnets and superconductors containing crystallographic clusters have been studied chiefly by nonlinear magnetic susceptibility (x_2) measurement. Effects of characteristic interaction at the heterogeneous boundaries have been discussed for the complex systems.First of all, a measurement system with a new cryostat apparatus was designed and constructed in order to observe nonlinear susceptibility under severe experimental conditions with both 1ow frequency and weak field amplitude. Using the system, we have been able to examine higher harmonics (up to 9'th order) as well as fundamental of the magnetic responses for each complex materia1.For CoCl_2-GIC,every harmonic component of the AC magnetization shows positive peak anomaly near the upper critical temperature, when the excitation amplitude (h) is larger than 0.6Oe. This fact confirms that x_2 shows negative divergence at the critica1 temperature. It is a1so proved to be an intrinsic phenomenon that the profile of the x_2 anomaly changes into anti-symmetric one when h becomes smaller than 0.3Oe.For ceramic superconductor YBa_2Cu_4O_8, x_2 shows sharp peak anomaly at a certain critical temperature enough below T_c of the crystalline specimens. This anomaly is speculated to be a reflection of frustrated phase ordering transition of the d-wave superconducting grains in the ceramics.For glassy magnet CaO-SiO_2-0.5Fe_2O_3, magnetic interaction between deposited ferrimagnetic clusters and amorphous boundary region around them is suggested. The interaction causes drastic descending shift of the ESR field as well as Curie-Weiss law of the DC susceptibility.In addition, despite several attempts to synthesize IBr-C_<60>, no spontaneous magnetization has been found in any compounds obtained by using various partial pressure of IBr for the doping.

几种含晶体团簇的复杂磁体和超导体主要是用非线性磁化率（x_2）测量来研究的。首先，设计并搭建了一套低温恒温测量系统，用于在低频弱场的苛刻实验条件下观测非线性极化率。利用该系统，我们已经能够检测各种复杂材料的高次谐波（最高可达9次）和基波磁响应。对于CoCl_2-GIC，当激励振幅（h）大于0.6Oe时，交流磁化强度的每个谐波分量在上临界温度附近都显示出正峰异常。这一事实证实了x_2在临界温度下表现出负发散。当h小于0.3Oe时，x_2反常曲线变为反对称曲线，这也是一种本征现象。对于陶瓷超导体YBa_2Cu_4O_8，x_2在低于晶体样品T_c的某一临界温度下出现尖锐的峰反常。对于玻璃态CaO-SiO_2- 0. 5Fe_2O_3磁体，这种反常现象可能是d波超导晶粒的有序相变受阻的反映.这种相互作用导致ESR场的急剧下降和直流磁化率的Curie-Weiss定律.此外，尽管有几次合成IBr-C_3的尝试，但<60>在任何使用不同IBr分压掺杂的化合物中都没有发现自发磁化。