PHASE TRANSITIONS OF COMPLICATED SPIN SYSTEMS WITH COMPETING INTERACTIONS AND DEPENDENCY OF THEIR PROPERTIES ON TIME-AND SPACE-SCALES OF OBSERVATIONS

一般来说，随机磁体根据观测的时间和空间尺度表现出多种形式的性质。在本项目中，我们对自旋玻璃（SG）系统、团簇玻璃（CG）系统和竞争各向异性系统进行了研究，通过观察(1)低场直流磁化强度，(2)高场磁化强度，(3)交流磁化率，(4)中子磁散射和(5)muSR光谱，并采用不同的时间和空间尺度的观测方法测量了这些参量。下面，我们总结了主要结果。[A] SG和CG体系(I)在SG体系Fe_xMn_<1-x>TiO_3上，我们在M_<ZFC>-T平面（H=const）和M_<ZFC> -H平面（T=const）上测量了零场冷却磁化M_<ZFC>在一定时间内的长时间弛豫，在此之后我们增加T（或H）。M_<ZFC>对T（或H）增加的响应表明M_<ZFC>是（T，H）的函数。这似乎与M_<ZFC>在T和h的长时间弛豫的存在不一致，但我们认为这些事实反映了SG系统复杂性质的多形式方面。(2)当M_<ZFC>（T，H）的值相同时，即使M_<ZFC>（T，H）的过程不同，M_<ZFC>（T，H）的弛豫过程也相似。我们推断，在SG（CG）系统中，till现象是普遍存在的。(3)在M_<ZFC>的磁化过程中，当H的扫频速率大于临界值时，M_<ZFC>跃迁至场冷值M_<FC>，这可以用多谷结构的分层组织模型来解释。(4)通过考察t循环和h循环对CG体系Fe_xMg_<1-x>TiO_3磁化弛豫现象的影响，提出CG体系也可以用层次组织模型来解释。(5) muSR测量表明，CG体系在冻结温度Tf附近的临界区域比SG体系的临界区域宽得多，这是由于在远高于Tf的温度下形成了磁团簇。[B]在竞争各向异性体系Fe_xCo_<1-x>TiO_3中，首先出现了自旋跃变，并伴随着横向自旋组分和纵向自旋组分的伸长和减少。这表明正交自旋分量是耦合的。少

In general, random magnets show multiform properties depending on time- and space-scales of observation. In this project, we investigated spin-glass(SG) systems, cluster-glass(CG) systems and competing anisotropy systems by observing the following quantities (1) low-field dc-magnetization, (2) magnetization up to high-field region, (3) ac-susceptibility, (4) neutron magnetic scattering and (5) muSR spectra, each of which was measured by using methods with different time- and space-scales of observation. Below, we summarize the main results. [A] SG and CG systems (I) On the SG system Fe_xMn_<1-x>TiO_3, we measured long-time relaxations of zero-field-cooled magnetization M_<ZFC> in the M_<ZFC>-T plane(H=const) and the M_< ZFC >-H plane(T=const) for a certain time tw and after tw we increased T(or H). The response of M_<ZFC> for the increase of T(or H) indicates that M_<ZFC> is a function of (T,H). This seems inconsistent with the existence of the long-time relaxation of M_<ZFC> at a cons … More tant T and H.However, we consider that these facts reflect the multiform sides of the complicated properties of SG systems. (2) When the value of M_<ZFC>(T,H) is the same even if M_<ZFC>(T,H) is reached by the different process, the relaxation of M_<ZFC>(T,H) proceeds similarly. We infer that tills phenomenon is common in SG(CG) systems. (3) In the magnetization process of M_<ZFC>, when the sweep-rate of H is larger than the critical value, M_<ZFC> jumps to the field-cooled value M_<FC>, which is explained by the hierarchical organization model with multi-valey structures. (4) From the examination of the effects of the T-cycle and the H-cycle on the relaxation phenomenon of magnetizations for the CG system Fe_xMg_<1-x>TiO_3, the CG system is suggested to be explained also by the hierarchical organization model. (5) The muSR measurement has clarified that the critical region of CG system around the freezing temperature Tf is much wider than that of SG system, which is due to the formation of magnetic clusters at temperatures much higher than Tf. [B] In the competing anisotropy system Fe_xCo_<1-x>TiO_3, the occurrence of the spin-flop transition accompanied with the elongation and the reduction of the transverse spin component and the longitudinal one was firstly shown. This indicates that the orthogonal spin components are coupled. Less