We have successfully developed a 1020MHz (24.0T) NMR magnet, establishing the world's highest magnetic field in high resolution NMR superconducting magnets. The magnet is a series connection of LTS (low-Tc superconductors NbTi and Nb3Sn) outer coils and an HTS (high-Tc superconductor, Bi-2223) innermost coil, being operated at superfluid liquid helium temperature such as around 1.8K and in a driven-mode by an external DC power supply. The drift of the magnetic field was initially ±0.8ppm/10h without the (2)H lock operation; it was then stabilized to be less than 1ppb/10h by using an NMR internal lock operation. The full-width at half maximum of a (1)H spectrum taken for 1% CHCl3 in acetone-d6 was as low as 0.7Hz (0.7ppb), which was sufficient for solution NMR. On the contrary, the temporal field stability under the external lock operation for solid-state NMR was 170ppb/10h, sufficient for NMR measurements for quadrupolar nuclei such as (17)O; a (17)O NMR measurement for labeled tri-peptide clearly demonstrated the effect of high magnetic field on solid-state NMR spectra.

Evidence for the quasi one-dimensional (1D) antiferromagnetism of CuO is presented in a framework of Heisenberg model. We have obtained an experimental absolute value of the paramagnetic spin susceptibility of CuO by subtracting the orbital susceptibility separately from the total susceptibility through the 63 Cu NMR shift measurement, and compared directly with the theoretical predictions. The result is best described by a 1D S = 1/2 antiferromagnetic Heisenberg (AFH) model, supporting the speculation invoked by earlier authors. We also present a semi-quantitative reason why CuO, seemingly of 3D structure, is unexpectedly a quasi 1D antiferromagnet.

The optical pumping NMR effect in the compensated semiconductor InP:Fe has been investigated in terms of the dependences of photon energy (E_p), helicity (sigma+-), and exposure time (tau_L) of infrared lights. The {31}P and {115}In signal enhancements show large sigma+- asymmetries and anomalous oscillations as a function of E_p. We find that (i) the oscillation period as a function of E_p is similar for {31}P and {115}In and almost field independent in spite of significant reduction of the enhancement in higher fields. (ii) A characteristic time for buildup of the {31}P polarization under the light exposure shows strong E_p-dependence, but is almost independent of sigma+-. (iii) The buildup times for {31}P and {115}In are of the same order (10^3 s), although the spin-lattice relaxation times (T_1) are different by more than three orders of magnitude between them. The results are discussed in terms of (1) discrete energy spectra due to donor-acceptor pairs (DAPs) in compensated semiconductors, and (2) interplay between {31}P and dipolar ordered indium nuclei, which are optically induced.Comment: 8 pages, 6 figures, submitted to Physical Review

23 Na NMR spectrum measurements in α ′ -NaV2O5 with a single-crystalline sample are reported. In the charge-ordered phase, the number of inequivalent Na sites observed is more than that expected from the low-temperature structures of space group Fmm2 reported so far. This disagreement indicates that the real structure including both atomic displacement and charge disproportionation is of lower symmetry. It is suggested that zigzag ordering is the most probable. The temperature variation of the NMR spectra near the transition temperature is incompatible with that of second-order transitions. It is thus concluded that the charge ordering transition is first-order.KEYWORDS: α ′ -NaV 2 O 5 , NMR, charge ordering, crystal structure, spin-ladder, trellis latticeSince the phase transition into a spin-gapped phase in α ′ -NaV 2 O 5 was reported, 1) a lot of experimental efforts have been devoted to understand the nature of this transition. Although it was initially identified as a spin-Peierls transition, a recent room-temperature structural study 2) questioned this interpretation: it concluded that all V ions are in a uniform oxidation state of V 4.5+and form a quarter-filled trellis lattice composed of twoleg ladders. After that, 51 V NMR measurements 5) revealed charge ordering of V 4+ and V 5+ states below the transition temperature T C ∼ 34 K. Subsequent theoretical studies showed that long-range Coulomb interaction can induce charge ordering in a quarter-filled trellis lattice. 6-9) These studies suggest zigzag or linear chain ordering depending on the strength of the longrange Coulomb interactions. The proposed mechanism of charge ordering is similar to that for charge density wave in quarter-filled systems of low-dimensional organic compounds, 10) suggesting some common physics to α ′ -NaV 2 O 5 and these systems. Soon after the finding of the transition, an x-ray diffraction measurement revealed superlattice formation of 2a × 2b × 4c in the charge-ordered phase, 11) but the detailed low-temperature structure has been unknown yet. Recently, two x-ray diffraction studies of the lowtemperature structure were reported. These indicate almost the same structure of space group Fmm2 , but their assignments of V electronic states are different. One suggests a structure consists of half-filled (V 4+ ) and empty (V 5+ ) ladders. 12) This charge distribution disagrees with a recent x-ray anomalous scattering measurement, which indicates charge modulation along b axis.13) The other suggests a structure including three different electronic state of V 4+ , V 5+ and V 4.5+ . 14) This structure is incom- * E-mail: ohama@physics.s.chiba-u.ac.jp patible with the 51 V NMR measurement, 5) which clearly shows that all the V sites split into two groups of V 4+and V 5+ states and that no V sites remains to be V 4.5+ . Thus, the low-temperature structure and the charge ordering pattern are still under discussion.In this letter, we report 23 Na NMR spectrum measurements with a single-crystalline sample. The obtained NMR spectra in the c...

81Br Nuclear quadrupole resonance (NQR) measurement was performed in an S = 1/2 one-dimensional Heisenberg antiferromagnetic metal complex [NiBr(chxn)2]Br2 (chxn: 1R,2R-diaminocyclohexane), having a halogen-bridged MX chain structure -Br-Ni3+-Br-Ni3+-Br-. Two 81Br NQR signals were observed below 40 K, while a single signal was observed above 130 K, showing the presence of two nonequivalent bridging Br sites below 40 K. This NQR result together with previously reported magnetic susceptibility and X-ray results indicate the occurrence of a transition into a spin-Peierls state between 40 and 130 K. This communication reports the first spin-Peierls transition in metal complexes in which pure d electrons contribute to the magnetism. In addition, we demonstrated a new experimental method for studying a spin-Peierls system.