Yuji Iwamoto

Temperature dependence of NMR spectrum at Cu(2) site in antiferromagnetic YBa2Cu3O6.1

The temperature dependence of the NMR spectrum at the Cu(2) site in antiferromagnetic YBa 2 Cu 3 O 6.1 was observed from 1.5 K to 77 K, well below the Neel temperature, in which the nuclear Zeeman and quadrupole frequencies, ν L and ν Q , were deduced. The frequency ν L ( T ) follows well the relation (ν L (0)-ν L ( T ))/ν L (0)= A T α above 10 K. The parameter values are evaluated as α=1.87, A =6.83×10 -6 ( K -α ) and ν L (0)=89.80 (MHz). The fact that the exponent α is close to 2 suggests the presence of gapless spin wave excitations. The coefficient A is two orders of magnitude larger than the value roughly estimated from the result of the neutron scattering experiment, which suggests the presence of larger low-energy excitations in the spin wave spectrum.

Temperature Dependence of the Sublattice Magnetization Measured by Cu NMR in Quasi-Two-Dimensional Antiferromagnet YBa2Cu3O6.1

The Cu-NMR spectrum for Cu(2) site was measured from 1.5 K to 200 K in the quasi-two dimensional (2D) bilayer antiferromagnet, YBa 2 Cu 3 O 6.1 . The nuclear Zeeman and quadrupole frequencies, ν L and ν Q were deduced from the spectrum. The decrease of the sublattice magnetization with increasing temperature was evaluated from the values ν L as (ν L (0)-ν L ( T ))/ν L (0) assuming no temperature dependence of the hyperfine coupling constant. The evaluated sublattice magnetization shows the almost linear temperature dependence at least above 25 K in log ((ν L (0)-ν L ( T ))/ν L (0)) vs. log T plot. This temperature dependence of the sublattice magnetization is well explained quantitatively within a factor of two by the spin wave model in the quasi-2D antiferromagnet using the exchange coupling parameters reported previously by neutron scattering experiments.

NMR and NQR studies of superconducting CeTIn5 (T=Co, Rh and Ir)

Abstract We have carried out 115 In and 59 Co nuclear quadrupole resonance and nuclear magnetic resonance measurements on CeTIn5 (T=Co, Rh and Ir). The temperature T- and the pressure P-dependence of the nuclear spin-lattice relaxation rate 1/T1 of 115 In in CeTIn5 indicated that the superconductivity occurred close to an antiferromagnetic instability. In the superconducting state, 1/T1 has no Hebel–Slichter coherence peak just below TC and a power-law T-dependence (1/T1∼T3) at very low temperatures, which indicates the existence of line nodes in the superconducting energy gap. The 115 In (Ce–In plane) Knight shift in CeCoIn5 decreases for both parallel and perpendicular directions to the tetragonal c-axis below TC, which shows that the spin susceptibility decreases in all directions. These results indicate that CeTIn5 (T=Co, Rh and Ir) exhibit non-s-wave even parity (probably d-wave) superconductivity.

55Mn NQR Study at Mn-II Sites in β-Mn Metal: A Possible Effect of Geometrical Frustration

55 Mn NQR measurements at the Mn-II site in a polycrystalline β-Mn have been performed over the wide temperature range up to 300 K. Fine structures in the NQR spectrum are newly observed below 100 ...

NMR and NQR Studies of 5f-Band Metal UCo0.95Ni0.05Al and UCo0.98Fe0.02Al

The 5 f -band system UCoAl, which crystallizes in the hexagonal ZrNiAl-type structure, has the enhanced paramagnetic ground state. The magnetic fields as low as 0.67 T oriented along the c -axis induce the metamagnetic transition below 17 K. Substitution effect for Co was studied by using Ni and Fe; the substitution of Ni stabilizes the paramagnetic state, and that of Fe stabilizes the ferromagnetic state. In order to study the origin of the magnetic-property change of UCo 1- x T x Al ( T = Ni, Fe), we performed 27 Al and 57 Co NMR/NQR measurements in UCo 0.95 Ni 0.05 Al and UCo 0.98 Fe 0.02 Al single crystals. The Knight shift and the nuclear spin-lattice relaxation rate T 1 -1 show the existence of the anisotropic spin fluctuations which are related with the potential ferromagnetic fluctuations among 5 f electrons in these materials.

Observation of unusual behavior in 55Mn NQR for MnII site in β-Mn metal

Abstract β-Mn metal is known not to show any magnetic ordering until low temperature, which is ascribed to an itinerant nearly antiferromagnet or a spin liquid state due to the geometrical frustration at MnII site. We have observed the sudden disappearance of the MnII-NQR signal accompanying by the rapid increase of the nuclear spin–lattice relaxation rate, T1−1 above about 200 K . The behavior T 1 −1 ∝ T below about 100 K is consistent with the self-consistent renormalization theory for itinerant nearly antiferromagnet, however, the unusual behavior described above is difficult to explain in this framework.