| Budget Amount *help |
¥13,300,000 (Direct Cost: ¥13,300,000)
Fiscal Year 1999: ¥3,100,000 (Direct Cost: ¥3,100,000)
Fiscal Year 1998: ¥10,200,000 (Direct Cost: ¥10,200,000)
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| Research Abstract |
The purpose for this study is the observation of actinide and rare earth NMR and the acquisition of typical examples with respect to the interaction between actinide or rare earth nucleus and electrons. This will be the starting point of our goal. The actinide and rare earth NMR is, however, very difficult to observe the signals because of poor natural abundance or too short relaxation time. We have tried detecting actinide and rare earth NMR signals in some materials. As the result, we succeed in the observation of ィイD1235ィエD1U and ィイD1171ィエD1Yb NMR in UOィイD22ィエD2 and YbBィイD212ィエD2, respectively. In the following, each summary is presented.
Seven ィイD1235ィエD1U resonance lines with a sharp line width have been observed in a 93% ィイD1235ィエD1U-ehriehed UOィイD22ィエD2 sample below 4.2 K and at zero magnetic field. This, is the first NMR observation for magnetic actinide ions. The hyperfine field at the U sites is evaluated as 252.3 ± 0.5 T, which is considered as the orbital field due to 5f-ele
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ctrons of the ィイD13ィエD1HィイD24ィエD2 state. Most interesting feature is that the electric quadrupole interaction at the ィイD1235ィエD1U sites is clearly observed in the antiferromagnetic state. In the strong LS coupling systems, an electric quadrupole interaction normally exists even in the cubic crystalline field if magnetic ordering is present, because the spatial alignment of the magnetic moments requires that of the orbital momentum and causes an axially symmetric charge distribution around the nucleus. In fact, the ィイD1235ィエD1U NMR spectrum indicates the axially symmetric electric field gradient (EFG) at the U sites. In addition, we quantitatively confirmed that the EFG is attributed to the reduction of symmetry of the 5f-wave function due to magnetic ordering.
The ィイD117ィエD1O NMR experiments were also performed to investigate the magnetic structure. The oscillation phenomenon due to the quadrupole splitting in the spin-echo decay is observed in the antiferromagnetic state. This clearly shows the Jahn-Teller distortion below TN. As the result, we conclude that a non-collinear 3q-strucure is most likely of the magnetic structures proposed by the neutron scattering experiments. It is very interesting that the EFG at the ィイD1235ィエD1U sites reflects the change of the 5f-wave function, that is, quadrupole ordering, while the EFG at the ィイD117ィエD1O sites reflects the change of the lattice, that is, the cooperative Jahn-Teller transition.
The ィイD1171ィエD1Yb NMR signal is observed below 10K in the single crystal of the Kondo semiconductor, YbBィイD212ィエD2, with the large shift of 66%. The hyperfine coupling constant is in good agreement with the orbital one calculated for a free YbィイD13+ィエD1 ion, indicating that the magnetic susceptibility at the low temperature limit is the Van-Vleck contribution within the J=7/2 multiplet. The nuclear spin-lattice relaxation rate at the YB site shows an activated temperature dependence below 15 K with the activation energy of 87 K, which, however, is completely different from the behavior at the B sites. The site-dependence may give us clue to reveal low energy excitations in the Kondo semiconductors. Less
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