| Research Abstract |
The purpose of this subject is the following two issues : one is to get the information on the superconducting energy gap appearing in the antiferromagnetic region of URu2Si2 under high pressure) the other is to get the origin on unusually small magnetic moment by Pt NMR in UPt3, where spin fluctuations are strongly suppressed by high pressure. For the purpose of getting the detailed structure of gap, we tried to measure the temperature dependence of nuclear spin relaxation rate down to 20 thru 30mK by a dilution refrigerator, because the superconducting transition temperature decreases drastically from 1.5 K with increasing pressure. However, the lowest temperature obtained in our dilution ref. is about 250 mK because of limited cooling power and a big high pressure cell (20mm in a diameter and 90mm in height). So we have to design the improved high pressure cell for the further NMR/NQR measurement at low temperatures. Fortunately, we could find weak 29Si NMR signal in the antiferromagnetic region of URu2Si2 attached in high pressure cell. Moreover, high pressure Si NMR revealed that the antiferromagnetic region obtained by applying high pressure is magnetically quite uniform with magnetic moment, of 0.3 μB. Secondly, we tried to purchase enriched 195 Pt for high pressure NMR measurement, because just a very weak Pt signal could be expected in the high pressure cell, if exists. The nominal (chemical) purity in enriched Pt was, however, 99.0 % thru 99.3 % for French and US products, though the enrichments were 99.8%. In order to have the sample of almost the same quality compared with the previously reported samples, more than 99.9 % in chemical purity is necessary at least. So we gave up to prepare UPt3 of high quality using enriched Pt. (290 words)
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