Magnetic Ordering Process in Geometrically Frustrated Systems

对几何阻挫体系的研究结果如下：1）CsNiCl_3型化合物的磁有序化过程CsFeBr_3和RbFeBr_3的NMR谱在T_N以下的一定温度范围内变为粉末状，表明相邻120 μ m结构磁性层的互相无规性。但目前还不知道这种随机性是静态的还是动态的。研究还发现，CsCoBr_3中温相的核磁共振信号是由于畴壁孤子引起的内场起伏而产生的，而畴壁孤子在低温相仍然存在。2）FeI_2的晶场分裂和磁相图用ESR和μ SR研究了FeI_2在100K附近的电子跃迁。FeI_2在强磁场中的磁化强度的测量表明，在强磁场中，FeI_2的磁化强度不随磁场的变化而变化。 ...更多信息 3）CuFeO_2Al掺杂对CuFeO_2自旋对称性的影响，使Ising自旋体系转变为Heisenberg自旋体系，但关于两个体系的交叉浓度以及共存的实验结果还不一致。角共享四面体三维竞争系统的基态在角共享四面体组成的Kagome晶格的SrCr_8Ga_4O_3中<19>，而中子自旋回波显示自旋冻结低于3.5K与磁化率观察到的场冷却效应一致。在Y（Sc）Mn_2中，虽然在0.07K以下的核磁共振弛豫时间没有发现异常，但在2K以下的muSR谱中也观察到自旋冻结，因此在具有角共享四面体的强阻挫体系中，自旋冻结在低温下。几何截断自旋系统的自旋冻结具有与随机自旋系统不同的特征。这种差异的解释是未来的问题。少

The results of the research on geometrically frustrated systems are as follow.1) Magnetic ordering process in CsNiCl_3-type compoundsNMR spectra of CsFeBr_3 and RbFeBr_3 turn to powder patterns in certain temperature range just below T_N indicating randomness of mutual phases of adjacent magnetic layrs with 120ﾟ structure. But it is not yet known whether the randomness is static or dynamic. It was also found that NMR signal in the intermediate temperature phase of CsCoBr_3 due to fluctuations of the internal field caused by domain wall solitons which was revealed to survive down to the low temperature phase. The magnetic structure at high magnetic fields of CsNiCl_3 was identified to be as predicted bu theory.2) Crystalline field splitting and magnetic phase diagram in FeI_2An electronic transition associated with the crystalline field splitting was observed around 100K by ESR and muSR in FeI_2. Measurements of magnetization on FeI_2 in intense magnetic fields revealed the absence of t … More he tricritical point speculated previously which may be related to the first order transition at T_N.3) Impurity effect on spin symmetry in CuFeO_2Al doping to CuFeO_2 was found to change the Ising spin system to a Heisenberg system, but the experimental results concerning the crossover concentration as well as the coexistence of both systems are not yet consistent with each other.4) Ground state of three dimensional competing system with corner shared tetrahedronsRemarkable spin fluctuations probed by muon spin relaxation survive down to 0.1K in SrCr_8Ga_4O_<19> with Kagome lattice composed of corner shared tetrahedrons, whereas neutron spin echo revealed the spin freezing below 3.5K consistently with the field cooling effect observed in the magnetic susceptibility. Similarly spin freezing was observed below 2K by means of muSR in Y (Sc) Mn2 although no anomaly in the relaxation time of NMR has been detected by NMR down to 0.07K.Thus in strongly frustrated systems with corner shared tetrahedronsan spins freeze at low temperatures. The spin freezin in the geometrically frusatrated systems has different features from that in random spin systems. The elucidation of the difference is a future problem. Less