Study of Nuclear Spin Ordering.

1.反铁磁共振：本课题的主要目的之一是观察超精细增强核自旋系统中的反铁磁共振现象。然而，在超精细增强核自旋系统中，AF共振很难观测到，部分原因是共振频率很高，在10 ~ 10^2MHz范围内，部分原因是rf测量场本身使核自旋升温太快。我们成功地观察到Ho（I=7/2）在Cs_2NaHoCl_6中的超精细增强核自旋的AF共振。部分测量设备由本次资助项目购置。从谐振场的温度依赖性，谐振频率与外加磁场图在0 K。这是第一次观察到增强的核反铁磁共振。我们还在另一个超精细增强核自旋系统HoVO_4中观察到了Ho核自旋的AF共振，结果比较复杂，理论分析正在进行中.纯金属中的核自旋有序：纯金属中的核自旋将通过两阶段退磁冷却来冷却。由于我们的补助金减少，我们无法购买第二个超导磁体。Cu核退磁冷却的第一阶段已经完成。

1. Antiferromagnetic Resonance: One of our main purpose of our project is to observe antiferromagnetic resonance(AF resonance) in hyperfine-enhanced nuclear spin systems. However,AF resonance in hyperfine-enhanced nuclear spin system is hard to observe,partly because the resonance frequency is rather high,ie,in the range of 10 to 10^2MHz,and partly because the rf measurement field itself warm up the nuclear spins so quickly. We succeeded to observe AF resonance of hyperfine-enhanced nuclear spins of Ho (I=7/2) in Cs_2NaHoCl_6 below T_N=4.5 mK Measurements were carried at several frequencies by cw NMR with a low field sweep. Some of measuring equipments were bought by the present Grant-in-Aid. From the temperature dependence of the resonance field, the resonance frequency versus applied field diagram at 0 K was obtained. This is the first observation of enhanced nuclear antiferromagnetic resonance. We also observed AF resonance of Ho nuclear spins in another hyperfine-enhanced nuclear spin system,HoVO_4.The results are rather complicated and the theoretical analysis is in progress.2. Nuclear spin ordering in pure metals: Nuclear spins in pure metal are going to be cooled down by tow stage demagnetization cooling. Due to the reduction of our Grant-in-Aid, we could not buy the second superconducting magnet. The first stage of the Cu nuclear demagnetization cooling has already been completed.