Study of Nuclear Spin Ordering.

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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.