The Physics and Chemistry of Quantum Magnetism

在这个项目中，我们对S=1准一维(Q1D)海森堡反铁磁体Ni(C_5H_&lt；14&gt；N_2)_2N_3(简称NDMAP)(简称NDMAP)进行了几个实验研究。从磁化强度对温度和磁场的依赖关系中，我们得到了有序相中自旋排列的信息。也就是说，在低温和强磁场下，自旋被限制在c平面内，并垂直于外场。根据NDMAP的电子自旋共振(ESR)测量，我们在低温和强磁场下观察到了两种信号，一种对应于反铁磁共振，另一种对应于一维激发。这一发现为理解S=1 Q1D反铁磁体中的磁激发提供了新的认识。我们还测量了氚化单…上的中子散射NdMAP的晶体较多，在高场和低温下发现了与长程磁有序有关的(0，1/2，1/2)点的Bragg峰，从而证实了场诱导LRO的存在。我们与理论物理学家合作，分析了NDMAP的磁场-温度相图。计算了具有单离子各向异性的一维S=1系统的交错磁化率，考虑了平均场形式的链间耦合的影响。理论计算结果很好地再现了我们所得到的实验相图。我们用脉冲中子源测量了La_6Ca_8Cu_(？)我们成功地观察到了梯形中低能激发的全色散曲线。通过对数据的分析，我们发现四自旋相互作用与大约10%的主要相互作用(腿和梯子)是必要的，才能得到合理的结果。此外，我们还研究了几个量子磁体，并获得了新的结果，详细情况在小册子中报道。较少

In this project, we have performed several experimental studies on the spin, S=1 quasi-one-dimensional(Q1D) Heisenberg antiferromagnet Ni(C_5H_<14>N_2)_2N_3(PF_6)(abbreviated NDMAP) for which a field induced magnetic long range ordering (LRO)has been discovered by the present investigator and co-workers. From the temparature and magnetic field dependence of the magnetization, we got information on the spin arrangement in the ordered phase. Namely, at low temperature and high magnetic fields, spins are confined in the c plane and directed perpendicular to the external field. From electron spin resonance(ESR)measurements on NDMAP, we observed two kinds of signals at low temperature and high magnetic field, one of which corresponds to an antiferromagnetic resonance and the other to a one-dimensional excitation. This finding Provides a new knowledge towards the understanding of magnetic excitation in an S=1 Q1D antiferromagnet. We have also measured neutron scattering on deuterated single … More crystals of NDMAP and found a Bragg peak at(0, 1/2, 1/2)point associated with the long range magnetic ordering at high field and low temperature, thus confirming that the field unduced LRO really exists.In collaboration with theoretical physicists, we have analyzed the magnetic field versus temperature phase diagram of NDMAP.We calculated the staggered susceptibility of S=1 one dimensional system with a single ion snisotropy taking into account the effects of the inter-chain couplings as the form of a mean-field. The theoretical result well reproduces the experimental phase diagram obtained by us.We have measured the magnetic excitations from the ladder part of La_6Ca_8Cu_<24>O_<41> using a pulsed neutron source. We were successful in observing a full dispersion curve for the low energy excitation in the ladder. From the analysis of the data, we found that a four spin interaction with about 10% of the dominant interactions(leg and ladder) is necessary to get a reasonable result.In addition to these, we have studied several quantum magnets and obtained new results, details of which are reported in the booklet. Less