Magnetic Ordering Process in Geometrically Frustrated Systems

几何受挫系统的研究结果如下：1) csnicl_3型化合物的磁有序过程CsFeBr_3和RbFeBr_3的snmr光谱在低于T_N的一定温度范围内转为粉末状，表明相邻磁层相互相的随机性。但目前尚不清楚这种随机性是静态的还是动态的。研究还发现，CsCoBr_3在中温阶段的核磁共振信号是由畴壁孤子引起的内场波动引起的，并且在低温阶段仍然存在。结果表明，CsNiCl_3在强磁场下的磁性结构与理论预测一致。2) fe_2在100K左右，用ESR和muSR观察到晶体场分裂的电子跃迁。在强磁场中对fe_2的磁化强度的测量表明，fe_2中没有T_N的存在，这是先前推测的三临界点，可能与T_N的一阶跃迁有关。3)发现CuFeO_2Al掺杂CuFeO_2时，杂质对自旋对称性的影响使Ising自旋体系转变为Heisenberg体系，但两体系的交叉浓度及共存实验结果尚不一致。4)角共享四面体的三维竞争体系的基态在角共享四面体组成的Kagome晶格中，在SrCr_8Ga_4O_<19>中，通过μ子自旋弛豫探测到的自旋波动在0.1K以下仍然存在，而中子自旋回波显示在3.5K以下的自旋冻结与磁化率中观察到的场冷却效应一致。在Y (Sc) Mn2中，通过muSR在2K以下观察到类似的自旋冻结，但在0.07K以下的核磁共振弛豫时间没有发现异常。因此，在具有角共享四面体自旋的强受挫系统中，低温会冻结。几何受挫系统中的自旋冻结与随机自旋系统中的自旋冻结具有不同的特点。对这种差异的解释是一个未来的问题。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