Study of the Ground State Properties in Random Magnetic Systems

它是当前项目的目标，以确定具有竞争自旋各异构体和竞争交换相互作用的随机磁系统的地面状态。对于竞争自旋各异构体系统的研究，我们选择了材料， &lt;Fe_（1-x）&gt;<Co_x><Cl_2>·2<H_2O>（FCC 2）、&lt;Fe_（1-x）&gt;<Co_x><Cl_2>（FCC）和&lt;Fe_（1-x）&gt;<Co_x><Br_2>（FCB）。这是从FCC 2上的中子散射研究中发现的，因为旋转组件完全是分裂的。FCC 2是一个与自旋不同物种竞争的理想抗磁网的例子。We have found &lt;Fe^（2+）&gt; localized magnetic excitations in the Co-rich antifer？magnetic phase of FCC2 from the ESR experiments at very high f\and field。从ESR实验的分析来看，它显示了&lt;Fe^（2+）&gt;旋转与&lt;Co^（2+）&gt;旋转甚至在共同丰富的阶段都形成了一个大的角度。我们对FCC和FCB进行了类似的研究。这些结果为我们提供了关于旋转顺序和与竞争旋转各形态的随机磁铁的地面状态特性的重要信息。由于对竞争交换交互系统的研究，我们选择了quasi-two-dimensional（2d）铁磁网和反磁网的随机混合<Rb_2><CrCl_4><Rb_2><MnCl_4>。&lt;<Rb_2>Mn_（1-x）&gt;<Cr_x>生长的单一晶体是由可疑<Cl_4>性和ESR测量的含义构成的。我们发现了随机磁铁是一个quasi-2d XY旋转玻璃（SG）的典型例子。据报道，没有材料显示了2d XY SG行为和<Rb_2>&lt;Mn_（1-x）&gt;<Cr_x><Cl_4>是2d XY SG的第一个示例。在富含铬的集中区，我们找到了一个重新活跃的旋转玻璃（RSG）过渡。核磁共振和中子散射实验展示了零场冷却RSG状态的测定铁磁域和涡流的结果。这些结果为我们提供了关于地面状态属性的重要信息。

It is the aim of the present project to clarify the ground state properties of the random magnetic systems with competing spin anisotropies and with competing exchange interactions.For the study of the competing spin anisotropies system, we have chosen the materials, <Fe_(1-x)> <Co_x> <Cl_2> ・2 <H_2O> (FCC2) , <Fe_(1-x)> <Co_x> <Cl_2> (FCC) and <Fe_(1-x)> <Co_x> <Br_2> (FCB). It is found from the neutron scattering study on FCC2 that the spin components are totally decoupled. FCC2 is the first example of an ideal antiferromagnet with competing spin anisotropies. We have found <Fe^(2+)> localized magnetic excitations in the Co-rich antiferromagnetic phase of FCC2 from the ESR experiments at very high frequency and field. From the analysis of the ESR experiments, it is shown that the <Fe^(2+)> spins make a large angle with the <Co^(2+)> spins even in the Co-rich phase. We have performed similar studies on FCC and FCB. These results give us important informations on the spin orderings and the ground state properties of the random magnets with competing spin anisotropies.For the study of the competing exchange interactions system, we have chosen the random mixture of a quasi-two-dimensional(2d) ferromagnet <Rb_2> <CrCl_4> and antiferromagnet <Rb_2> <MnCl_4> . The single crystals of <Rb_2> <Mn_(1-x)> <Cr_x> <Cl_4> grown for this study have been characterized by means of susceptibility and ESR measurements. It is found that the random magnet is a typical example of a quasi-2d XY spin-glass(SG). No material has been reported that exhibits a 2d XY SG behavior, and <Rb_2> <Mn_(1-x)> <Cr_x> <Cl_4> is the first example of a 2d XY SG. In the Cr-rich concentration region, we found a re-entrant spin-glass(RSG) transition. The NMR and neutron scattering experiments show that the zero field cooled RSG state consists of ferromagnetic domains and vortices. These results give us an important information on the ground state properties of the 2d XY SG.