NMR Frequency Shift Research Articles

Theory of Solid Hydrogen Mixture. I. Distribution of Local Order Parameters, NMR Line Shapes and Relaxation Times

The ortho-para mixture of solid H 2 is studied theoretically for fcc lattices of finite size, assuming EQQ interaction. The excitation spectrum is calculated by using the Hartree ground-state obtained numerically. The lowest excitation energy decreases with decrease of ortho concentration X , and vanishes at X ∼ 0.55. The distribution of the local order parameters (LOP) is obtained in comparison with NMR line shape. Importance of the quantum effect is pointed out for the distribution of LOP which broadens rapidly with decrease of X . The relaxation time T 1 is also studied as a function of NMR frequency shift, manifesting that ortho-H 2 with smaller value of order parameter relaxes more rapidly in the quadrupolar glass region.

Synthesis of [guanidino-13C]creatine and measurement of the creatine phosphokinase reaction in vitro by 13C NMR spectroscopy.

[guanidino-13C]Creatine has been synthesized by reaction involving synthesis of [13C]cyanamide followed by its condensation with sarcosine. The creatine guanidino carbon 13C NMR frequency shifts upon the formation of phosphocreatine by 0.83 ppm with a splitting (2JCP = 3.3 Hz) due to two-bond phosphorus-carbon coupling. The high 13C enrichment (99%) at the guanidino carbon of creatine gave rise to an adequate signal-to-noise ratio for both creatine and phosphocreatine so that a study of the time course of the creatine phosphokinase reaction could be performed and provided the means for a determination of the Km (15.5 mM) of the reaction.

The spin echo in systems with a coupled electron-nuclear precession

I. Introduction 235 II. Theoretical concepts 237 ???1. Basic aspects of NMR in magnetic crystals. 2. Dynamics of nuclear magnetization with a dynamic frequency shift in a transverse rf field. 3. Induction and echo. 4. Frequency-modulated echo. III. Experimental research 244 ???5. Measurement methods. 6. Magnetically ordered crystals which have been studied. 7. Free-induction signal. 8. Spin-echo signals. 9. Spin systems with a small dynamic NMR frequency shift. 10. Dynamic NMR frequency shift of nuclei in domain walls. IV. Conclusion 253 References 254

Magnetic Vortices in Rotating SuperfluidHe3-B

Rotating superfluid $^{3}\mathrm{He}$-$B$ is found to possess a new contribution to the NMR frequency shift, which changes sign on reversal of either the angular velocity of rotation or the magnetic field. For $p=29.3$ bars this gyromagnetic effect shows a discontinuity in magnitude at the first-order phase-transition temperature $\frac{T}{{T}_{c}}=0.6$, at which a change in the vortex-core structure takes place. These observations support the conclusion that the vortex core possesses a spontaneous intrinsic magnetization.

Experimental studies of solitons in superfluid 3He-A

Magnetic textures have been created and studied in the A phase of superfluid 3He at several pressures, in magnetic fields from 15 to 20 mT, by intense rf magnetic pulses which invert the magnetization of the fluid. To create this new state we find that the initial large pulse must tip the magnetization by at least 140‡. In this state the fluid evolves from a condition where the NMR frequency shift Ω-γH 0is smaller than that in the unperturbed superfluid by a factor of 0.54, over a time scale of tens of seconds to a condition where the frequency shift is 0.70 times the unperturbed value. We have studied the fluid's linear response to small-angle sampling pulses as well as the nonlinear response to large-angle pulses. By using two independent NMR coils we have seen this new state move through the fluid; we find that a lower limit on its propagation velocity is around one-half the spin wave velocity. All of our results are generally consistent with the model of solitons in the order parameter proposed by Maki and co-workers.

Theory of the anomalous behavior of the NMR frequency shift near the liquid-vapor critical point

Theory of the anomalous behavior of the NMR frequency shift near the liquid-vapor critical point

Effect of pressure on the crystal field splitting in rare earth pnictides and chalcogenides

The experimental situation for the pressure dependence of the crystal field of praseodymium pnictides and chalcogenides is reviewed and compared with the predictions of the point charge model. The problem of separating exchange and crystal field contributions from the measured NMR frequency shift or susceptibility measurements is discussed as well as problems explaining these effects with conduction electron related models.

Texture relaxation in 3He-A

Metastable magnetic textures are created in 3He-A using pulsed NMR and subsequent frequency shifts are analyzed. The results are consistent with a model for splay composite solitons, assuming the NMR pulse produces these solitons at a high density.

Study of the orientational electric field effect in 3He-B

We have studied the orienting effect that an electric field has on the orbital motion of the pairs in superfluid 3He-B, using the orientation-dependent transverse NMR frequency shift as a probe. This method provides high resolution for studying the orienting effect for either sign of the orientational energy. Electric fields as high as 35,000 V/cm applied across the sample produced no measurable frequency shift at 0-, 10-, and 32-bar pressures. This gives upper limits to the orientational energy of 1.4 × 10\s-3, 1.0 × 10\s-3 and 4 × 10\s-4 times the values expected from simple theory.

Temperature and volume dependence of some magnetic properties of Pr-pnictides

Several experiments relating to the volume dependence of crystal field interactions in rare earth pnictides have been carried out. These experiments include measurements of 1) the temperature dependence of the susceptibility of PrN, 2) the room temperature compressibilities of PrN and PrAs, 3) the NMR frequency shifts for 141Pr in PrN and PrSb, and 4) the low-temperature pressure dependence of the 141Pr frequency shift in PrN and PrSb. Although electrostatic screening effects on crystal field interactions in PrN are smaller than in the heavier Pr- pnictides, the anomalous volume dependence of the 141Pr NMR shift is essentially the same in all these compounds.

Magnetism of V-doped Ti2O3

Abstract Adding V-atoms introduces localized spins in Ti2O3. The NMR frequency shift of 51V does not follow the susceptibility, which might suggest that V atom is nonmagnetic. The NMR absorption intensity decreased with increasing V concentration. At low temperatures, V-doped Ti2O3 shows spin glass behavior.

Pulsed NMR frequency shifts in superfluid 3He

We report the first measurements of the NMR frequency in 3He A and B under conditions where the net magnetization, M , is tipped far from its equilibrium direction along H O. In 3He A the frequency shift ω - γ H O varies from the continuous wave value at tipping angle Φ = 0 to a negative shift at Φ = 180°. In 3He B no frequency shift is observed, however for Φ ≳ 100° a beat pattern is seen to develop in the free induction decay envelope.

The likelihood of f-wave pairing in superfluid3He

The minimization of the Landau free-energy functional for f-wave pairing near Tc has been studied to find models for the A1, A and B phases of superfluid 3He. While models can be found which fit the NMR data in each separately, the resulting ratio of the longitudinal NMR frequency shifts in the B and A phases at the polycritical point disagrees with the experimental value even more than the ratio predicted from p-wave pairing. The theoretical techniques underlying the discussion exploit representations of the point groups in order to construct models for certain special, but physically important, types of phase called inert. Inert phases possess order parameters which do not vary continuously with the strong-coupling coefficients specifying the dynamics.

Transverse NMR Measurements on SuperfluidHe3

Transverse NMR measurements on liquid $^{3}\mathrm{He}$ are reported down to 0.7 mK at several pressures below 27 bar. In the $A$ liquid the quadratic NMR frequency shift is proportional to ${{T}_{C}}^{2}(1\ensuremath{-}\frac{T}{{T}_{C}})$. In the $B$ phase the integrated dynamic susceptibility falls to a limiting value which is 25% of the Fermi-liquid susceptibility. NMR data on the $A$ and $B$ liquids confined in the voids of fine powder are also presented.

Memory effects in the NMR frequency shifts

The narrowing of the heat-bath correlation function by decreasing the sample temperature in a molecular system with a cooperative motion, causes the shifting of the NMR resonance frequency, as predicted by the memory-function approach.

Anomaly in the NMR shifts of P and As in CeP and CeAs

The NMR frequency shifts for 31P and 75As in the compounds CeP and CeAs have been measured between the Néel point and 200°K. Between 10 and 60°K the ratio of resonance shift to bulk magnetic susceptibility, expected to be independent of temperature, was found to increase with increasing temperature by approximately a factor of two. Possible causes are temperature dependent or non-linear hyperfine couplings.

Proton Magnetic Resonance and Optical Spectroscopy of [Ni(MeOH)5Cl]+ in Methanol

A proton magnetic resonance and optical spectroscopy study of the complex formation of Ni2+ with Cl− in methanol is reported. NMR studies were made between − 70° and + 100°C. At low temperatures (below − 20°C) in solutions containing both Ni2+ and Cl− it is possible to detect an NMR signal due to a superposition of the solvation shells of [Ni(MeOH)6]2+ and of [Ni(MeOH)5Cl]+. Between − 15° and + 30°C fast exchange smears out the part of the peak due to the monochloro complex; from the decrease in the intensity of the remaining signal, equilibrium constants as function of temperature are determined. From the variation of the bulk-methanol NMR linewidth and frequency shift with temperature the following kinetic parameters and hyperfine interaction constants for the solvation-shell molecules of [Ni(MeOH)5Cl]+ are found: specific rate of exchange at 25°C, 2.3 × 105sec−1; activation energy for the exchange reaction, 15.8 kcal mole−1; hyperfine interaction constants for the methyl and hydroxyl protons, + 0.51 and + 0.37 Mc/sec, respectively. Optical spectroscopy measurements were made at − 40°, + 23°, and + 50°C. Analysis of these data provided evidence that the nickel–chlorine complex formed is a monochloro pseudo-octahedral complex, i.e. [Ni(MeOH)5Cl]+.

Nuclear magnetic resonance measurements in PtP 2 and PtAs 2

The 31P, 75As and 195Pt NMR have been observed in PtP 2 and PtAs 2. The 31P and 195Pt NMR frequency shifts were found to be temperature independent. Also reported is the 75As NQR in PtAs 2.

Observation of thePr141andTm169Nuclear Magnetic Resonances in the Paramagnetic States of Rare-Earth Intermetallic Compounds

The first observations of the ${\mathrm{Pr}}^{141}$ and ${\mathrm{Tm}}^{169}$ nmr in rare-earth intermetallic compounds are described. The calculated and observed values for the nmr frequency shifts are in good agreement.

NMR and Magnetic Susceptibility of Co Magnetic Impurities in Transition Metal Hosts

The 59Co NMR has been observed in Mo-y at. % Co and W-x at. % Co alloys where: y=0.54 and 1.08; x=0.53 and 1.05. The NMR frequency shifts exhibit a strong temperature dependence which can be correlated with the temperature dependent part of the bulk susceptibility. The resonance lineshapes are symmetrical and the linewidths show a temperature and field dependence which is approximately linear in H/T. The magnetic susceptibilities can be fitted to an equation of the Curie-Weiss form: χ−χ0=C/(T−θ) with θ∼−11°K and −24°K for the W and Mo hosts, respectively. In each alloy the temperature-independent susceptibility is approximately equal to that of the host metal, and the values of the Curie constant correspond to ``effective'' moments per Co atom (gS) of 1.79±0.10 in W and 1.52±0.15 in Mo. Using temperature as an implicit parameter over the range of 4.2°–300°K, a plot of the Knight shift vs susceptibility for each alloy yields a linear relationship from which the hyperfine field per Bohr magneton is found to be much smaller than expected for Co. Assuming pure d states this suggests that the ``effective moment'' in these alloys does not reside entirely on the Co atom, and the host matrix is polarized in the vicinity of the impurity; however an alternate explanation is that positive contributions to the internal field such as an admixture of s character into the d states of the impurity tend to cancel the large negative hyperfine field due to core polarization by the unpaired d spins.