We report NMR measurements of the spin density wave (SDW) transition critical fluctuations in (TMTSF)2PF6 at 14.9 MHz and 0.98 GHz. This contribution to 1/T1 is nearly independent of the magnetic field alignment and the frequency on both sides of the transition; above the transition at TN it varies as ¦T − tn¦θ with θ = −0.75 ± 0.08. These observations are consistent with dynamical scaling for the 3D Heisenberg model and show that the correlation time for the critical fluctuations responsible for t1 is less than 2 × 10−10 s for all temperatures studied. Such behavior is very different from that observed in the ordered SDW phase, where the dominant coupling is to SDW phasons whose characteristic times cover a very broad range.

We report the annealing of a strained flux line lattice (FLI) in 10 mu m diameter type-II superconcducting NbTi filaments by an rf magnetic field at 4.2 K in a magnetic field of 1 T. The strained FLL is prepared by slowly changing the direction of the applied magnetic field When the rf magnetic field used to generate a Nb-93 NMR spin echo anneals the FLL, there is a corresponding reduction in the amplitude of the spin echo. Starting from an annealed condition, a rotation threshold of 3 mr is needed to produce enough FLL strain to be observed in these measurements.

We present an extensive NMR study of the spin-1/2 antiferromagnetic Heisenberg ladder Cu-2(C5H12N2)(2)Cl-4 in a magnetic field range 4.5-16.7 T. By measuring the proton NMR relaxation rate 1/T-1 and varying the magnetic field around the critical field H-c1 = Delta/g mu(B) approximate to 7.5 T, we have studied the transition from a gapped spin liquid ground state to a gapless magnetic regime which can be described as a Luttinger liquid. We identify an intermediate regime T greater than or equal to \H - H-c1\, where the spin dynamics is (possibly) only controlled by the T = O critical point H-c1.

We present an overview of NMR data on the inorganic spin-Peierls compound CuGeO3 in its uniform and dimerised phase, and focus on its high magnetic field incommensurate phase. In this latter phase the analysis of the NMR line shape provide the first detailed microscopic picture of the local spin-density corresponding to a magnetic soliton lattice.

We present an overview of NMR data on the inorganic spin-Peierls compound CuGeO3 focusing on its high magnetic field incommensurate phase. In this phase, the analysis of the NMR line shape provide the first detailed microscopic picture of the local spin density corresponding to a magnetic soliton lattice. While on a qualitative level the temperature and magnetic field dependence of this soliton lattice correspond to the theoretical predictions, quantitative disagreements may provide important information on the effects of quasiparticle interactions, interchain coupling and magnetoelastic coupling. The field dependence of the line shape also indicates that the incommensurate phase may be divided into sub-phases with one hypothetical transition line situated near 26T.

The role of NMR measurements for investigating the properties of incommensurate spin density waves (ISDW) in solids is reviewed and several new measurements of these properties are presented in (TMTSF)2PF6 and the alloy (TMTSF)2(P0.5As0.5F6. These result include proton spin echo measurements of the temperature dependence of the spin density wave magnetic field, and the depinning electric field threshold and real part of the dielectric constant as a function of frequency and temperature. The relation between the spin-lattice relaxation rate and the imaginary part of the dielectric constant is presented and compared qualitatively with measurements. Measurements of the sliding SDW velocity using spin echoes and narrow band noise are reported. They show that the pinning potential period is half the wavelength of the SDW.

A novel method of Fourier transform spectroscopy of the transient signals from wide, inhomogeneously broadened magnetic resonance spectra is described and analyzed. It has the advantages of high resolution, high sensitivity, and freedom from the distortions introduced by the finite amplitude of the pulsed rf magnetic field and the finite bandwidth of the receiving system. It consists of recording the transient signal at a series of magnetic fields, shifting the frequency of the transient by the corresponding field step for each point, and summing the corresponding Fourier transformed signals. Although the primary emphasis is on pulsed NMR, the analysis also applies to pulsed ESR. Criteria for the range and step interval of the magnetic field variation are discussed. The accuracy and sensitivity of the method are compared with earlier methods of spin echo spectroscopy. A description of the corresponding measurement of NQR, NMR, and ESR spectra obtained by stepping the frequency of the spectrometer is also presented.

Measurements of the $^{11}\mathrm{B}$ NMR spectrum, isotropic Knight shift (${\mathit{K}}_{\mathit{i}}$), and spin-lattice relaxation rate (1/${\mathit{T}}_{1}$) in an unoriented powder sample of ${\mathrm{YNi}}_{2}$${\mathrm{B}}_{2}$C are reported in the normal and the superconducting states. In the normal state, ${\mathit{K}}_{\mathit{i}}$ varies linearly from (+5.7\ifmmode\pm\else\textpm\fi{}0.7) \ifmmode\times\else\texttimes\fi{} ${10}^{\mathrm{\ensuremath{-}}4}$ at 300 K to (+4.9\ifmmode\pm\else\textpm\fi{}0.7)\ifmmode\times\else\texttimes\fi{}${10}^{\mathrm{\ensuremath{-}}4}$ just above the superconducting transition temperature. The anisotropic Knight shift, if present, is substantially smaller than ${\mathit{K}}_{\mathit{i}}$. An anomalous increase in (${\mathit{T}}_{1}$T${)}^{\mathrm{\ensuremath{-}}1}$ with decreasing temperature (T) is found in the normal state. From the behavior of the NMR linewidth in the superconducting state, the low-temperature limit \ensuremath{\lambda}(0)=(108\ifmmode\pm\else\textpm\fi{}5) nm is found for the penetration depth. At the superconducting transition, 1/${\mathit{T}}_{1}$ drops rapidly and no Hebel-Slichter peak is seen.

We report measurements of the velocity of the sliding spin-density-wave (SDW) condensate in (TMTSF)2PF6, where TMTSF is tetramethyltetraselenafulvalene from their modulation of the proton spin echo as a function of the SDW current. From these measurements and those of the sliding SDW noise we find that the velocity is consistent with the entire condensate participating in the charge transport and that the wavelength of the pinning potential is half that of the SDW.

Analysis of the proton NMR lineshape in (TMTSF)2PF6 near the spin density wave (SDW) transition at 12.1 K shows that both the metallic and SDW phases coexist with a disconstinuous jump in the order parameter at the transition. This behavior is evidence that the transition is first order.

We report NMR spin echo measurements of the average spin density,wave condensate displacement at 4.2 K in (TMTSF)2PF6 When it is driven by an electric field below the depinning threshold over time scales of 10-25 mus. The displacement, which corresponds to internal deformations, varies linearly as a function of the electric field and has a restoring force constant per electronic charge k = ( 1.3 +/- 0.3) x 10(-9) N/m. At the depinning threshold the average condensate displacement is 0.46 +/- 0.06 angstrom. The corresponding low frequency dielectric constant is (3.4 +/- 0.7) x 10(9), which is close to that obtained from electrical transport measurements.

Measurements of the proton spin-lattice relaxation rate (1/T 1 ) at a pressure of 1 bar in a single crystal of (TMTSF) 2 PF 6 (TMTSF is tetramethyltetraselenafulvalene) are reported for the magnetic field in the range 0.25-1.48 T aligned along the b'- and c'- axes over the temperature range 2-30 K. The methyl group rotation contribution to 1/T 1 is subtracted to obtain the spin density wave (SDW) contribution. Through measurements of 1/T 1 below and above the spin flop transition it is determined that phason fluctuations of the SDW are responsible for most of the relaxation. Depinning the SDW's by an electric field leaves 1/T 1 nearly unchanged, which indicates that the SDW and its fluctuation rate near 10 8 rad/s persist when the SDW is sliding. Analysis of the peak in 1/T 1 near 3 K on the applied magnetic field suggests that it represents a slowing of thermally activated fluctuations with an activation energy Δ/k B =18.3±4.0 K, which is close to the single particle gap for this material. The contribution of critical fluctuations to 1/T 1 is consistent with the transition being weakly first order. Unlike the relaxation in the ordered phase, the contribution of the critical fluctuations is isotropic and has little, if any dependence on magnetic field

We report low field proton NMR measurements in the spin density wave (SDW) state of (TMTSF${)}_{2}$${\mathrm{PF}}_{6}$ that show a narrowing of the linewidth when the SDW is depinned by an electric field. The NMR absorption amplitude affirms that sample heating is negligible. A shortening of the spin-phase memory time corresponding to the line narrowing is also observed. Low field measurements of the spin-lattice relaxation rate show a fluctuation enhancement just below the spin density wave transition and a rapid drop below 3 K that lack a quantitative understanding.

We present elastic constant data of the material (TMTSF)2PF6, with particular emphasis on the region about the phase transition, and at low temperatures. Specific heat, resistivity, and NMR measurements have indicated a very sharp transition at T(SDW) = 12.1K. Similarly sharp features have been observed in the temperature dependence of the Young's Modulus, followed by a continual stiffening below the transition. Comparison to recent NMR results indicate that the modulus varies as the square of the internal magnetic field below T(SDW), thus constraining the form of the coupling of the order parameter to the strain field. There is no evidence for anomalies in the modulus below 4K, where it has been suggested that a transition to a commensurate state occurs.