Tetsuo Ohama

23Na NMR Study of Spin-Peierls Transition in NaV 2O 5

23 Na NMR spectrum measurements in a spin-Peierls system, NaV 2 O 5 , are presented. Below the spin-Peierls transition temperature ( T sp ), two distinct sites of Na appear, confirming the structural phase transition at T sp . The orbital susceptibility was evaluated using the temperature dependence of the 23 Na NMR shift; it is suggested that the orbital susceptibility changes near T sp . The temperature dependence of the spin susceptibility obeys an activation law below ∼20 K with a gap of 98 K.

Anomalous Transferred Hyperfine Coupling in CeCu2Si2

The magnetic susceptibility and the Cu and Si Knight shifts have been measured in CeCu 2 Si 2 . The transferred hyperfine couplings at both the sites are strongly temperature-dependent and noticeably anisotropic at low temperatures. The negative hyperfine couplings observed for the magnetic field along the c -axis at the low temperatures are anomalous as in Ce intermetallic compounds. It is pointed out that the transferred hyperfine coupling due to the hybridization of the f electrons with the ligand s electrons can be anisotropic and also can reverse its sign at the lower temperatures than the crystal-field splitting energy. It is concluded that this hybridization is the dominant mechanism of the transferred hyperfine coupling and responsible for the anomaly.

The d Orbital Character in the Spin-Peierls System NaV 2O 5

51 V NMR measurements in the uniform state of NaV 2 O 5 are presented. The NMR shift and the electrical field gradient (EFG) were measured at the tetravalent V sites. Observed anisotropy of the NMR shift and the EFG indicates that the d x y -like orbital is occupied. It has been found that the orbital susceptibility in the uniform state is significantly smaller than the residual susceptibility in the spin-Peierls state. The possible origins of this disagreement are discussed.

51V NMR study of spin gap in CaV4O9

The NMR shift and the nuclear spin-lattice relaxation rate (1/ T 1 ) were measured at the V sites in the two-dimensional compound CaV 4 O 9 . The NMR shift becomes a positive constant below ∼15 K, indicating that the intrinsic spin susceptibility vanishes at low temperatures. The activated T dependence of 1/ T 1 has revealed the dynamical spin gap Δ R ∼104 K, which is rather smaller than the static spin gap determined from the susceptibility Δ S ∼135 K.

NMR Study of Magnetic Excitations in CeNiSn

The anisotropies of the Knight shift and the nuclear spin-lattice relaxation time ( T 1 ) at the Sn sites have been measured up to 300 K with a magnetically aligned powder sample of CeNiSn. In contrast to the results of previous neutron scattering measurements, the anisotropy of 1/ T 1 is weak and almost temperature ( T )-independent. This indicates that the substantial spectral weight exists in the higher energy region than the quasielastic magnetic excitation at high T . Above about 60 K, 1/ T 1 increases linearly with T , suggesting that the T dependence of the quasielastic line width is weak.

Hybridization Effects on Conduction-Electron Polarization and Two-Ion Coupling in PrCu2Si2

The temperature dependence and the anisotropy of the magnetic susceptibility and the Knight shifts have been measured in PrCu 2 Si 2 and GdCu 2 Si 2 with magnetically aligned powder samples. For GdCu 2 Si 2 , the isotropic s-f exchange model provides a good description of its magnetic properties, but in PrCu 2 Si 2 an anisotropic two-ion coupling has been found. It has been revealed that the hyperfine coupling at the Si sites is enhanced in PrCu 2 Si 2 , thereby suggesting preferential hybridization of the f-electrons with the Si valence electrons. This effect is responsible for the unusually high Neel temperature of PrCu 2 Si 2 .

NMR and NQR studies of a semiconducting compound U3Ni3Sb4

The 121 Sb Knight shift and the 121,123 Sb nuclear spin-lattice relaxation time T 1 in U 3 Ni 3 Sb 4 have been measured. In the temperature range between 25 and 250 K, 1/ T 1 , which has been measured by nuclear quadrupole resonance (NQR), follows an activation law with an activation energy of 21.1 meV. The relaxation process is dominated by the magnetic contribution. The Knight shift is represented as the sum of a strongly temperature-dependent anisotropic term and a temperature-independent term. The transferred hyperfine field from the U 5 f electrons through the U 5 f -Sb 5 p hybridization makes an important contribution to the Knight shift.

Spin Excitations in the Two-Leg Ladder Antiferromagnet CaV2O5.

The nuclear spin-lattice relaxation rate (1/ T 1 ) at the V sites in CaV 2 O 5 was measured. The relaxation rate in the two-leg ladder was calculated with a strong-coupling expansion ( J ⊥ ≫ J ∥ ), and the result was compared with the experimental data. The comparison of the temperature dependence shows a good agreement and provides an estimate of both J ⊥ and J ∥ as well as the energy gap Δ. The magnetic field dependence of 1/ T 1 is also reproduced with this approximation in the temperature range \(T \lesssim \Delta/4\). It is found that the magnon-magnon collision, which leads to a diffusive behavior, is negligible in this temperature range. The effect of inter-ladder coupling is investigated and found to be weak in CaV 2 O 5 . Thus the strong-coupling expansion calculation a grees satisfactorily with the experimental data, but a discrepancy between the exchange parameters deduced from the magnetic susceptibility and 1/ T 1 is found.

Itinerant Character of 5f Electrons in UNi2Ga

NMR and NQR measurements have been made for Pauli paramagnetic UNi 2 Ga. The temperature dependence of the Knight shift and the nuclear relaxation rate 1/ T 1 at the Ga sites has been measured between 4.2 K and 290 K. Fermi liquid behavior, that is, temperature-independent Knight shift and 1/ T 1 proportional to temperature, has been observed over the measured temperature range. A quantitative analysis suggests that the enhancement of the wave-vector-dependent susceptibility χ( q ) is fairly localized near q ∼0 in q space.

Dynamical magnetic properties of U3Co3Sb4

Abstract In the metallic compound U3Co3Sb4, the nuclear spin-lattice relaxation time T1 and the NQR frequency vQ at the Sb sites have been measured. The temperature dependence of T1 and vQ can be understood as the properties of a nearly ferromagnetic metal.