{23}Na nuclear spin-lattice relaxation studies of Na2Ni2TeO6

We report on {23}Na NMR studies of a honeycomb lattice antiferromagnet Na2Ni2TeO6 by {23}Na nuclear spin-echo techniques. The {23}Na nuclear spin-lattice relaxation rate 1/{23}T_1 exhibits critical divergence near a Neel temperature T_N = 26 K, a narrow critical region, and a critical exponent w = 0.34 in 1/{23}T_1 = a (T/T_N - 1)^{-w} for Na2Ni2TeO6, and T_N = 18 K for Na2(Ni{0.5}Cu{0.5})2TeO6. Although the uniform magnetic susceptibility of Na2Ni2TeO6 exhibits a broad maximum at 35 K characteristic of low dimensional spin systems, the NMR results indicate three dimensional critical phenomenon around the Neel temperature.Comment: 4 pages, 6 figure

7Li NMR Studies of LiCrO2

We report on 7Li NMR studies of a spin S = 3/2 triangular lattice antiferromagnet LiCrO2 (Neel temperature TN = 62 K) in the paramagnetic state by using the free-induction decay of 7Li nuclear magnetization. We observed critical divergence of the 7Li nuclear spin-lattice relaxation rate 1/T1 near TN, a narrow critical region, and a critical exponent w = 0.45 from a fit of 1/T1 $\propto$ (T/TN - 1)$^{-w}$. Although spin frustration effects have been explored for this system, the dynamical critical phenomena suggest that LiCrO2 in the critical region is a poor low dimensional antiferromagnetic system.Comment: 6 pages, 4 figures, to appear in JPS Conf. Proc. (SCES2013

Near-Infrared Spectroscopy of Very Low-Luminosity Young Stellar Objects in the Taurus Molecular Cloud

We have carried out near-infrared spectroscopic observations of 23 very low-luminosity young stellar object (YSO) candidates and 5 their companions in Heiles Cloud 2, one of the densest parts of the Taurus molecular cloud. Twelve objects were confirmed as YSOs by Br gamma feature. The effective temperatures of the YSOs and of the companions are estimated from the 2.26 micron feature, the 2.21 micron feature, and the H2O band strengths. Detailed comparisons of our photometric and spectroscopic observations with evolutionary tracks on the HR diagram suggest some objects to be very low-mass YSOs.Comment: 15 pages, 19 figures. PASJ accepte

Site-selective 63^{63}Cu NMR study of the vortex cores of Tl2_{2}Ba2_{2}CuO6+δ_{6+\delta}

We report site-selective $^{63}$Cu NMR studies of the vortex core states of an overdoped Tl$_{2}$Ba$_{2}$CuO$_{6+\delta}$ with $T_{c}$ = 85 K. We observed a relatively high density of low-energy quasi-particle excitations at the vortex cores in a magnetic field of 7.4847 T along the c axis, in contrast to YBa$_{2}$Cu$_{3}$O$_{7-\delta}$.Comment: 5 pages, 6 figures, submitted to J. Phys. Chem. Solids (QuB2006, Tokai