Magnetic resonance spectral reconstruction using frequency-shifted and summed Fourier transform processing

Abstract

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.

High-magnetic-field NMR studies ofLiVGe2O6:A quasi-one-dimensional spinVonlanthen1, Tanaka2, Goto3 et al. 2002Phys. Rev. BSelf Cite215190View full textAdd to dashboardCite

“…This can be seen from Fig. 17, where ∆ν for the two peaks in the 7 Li spectrum caused by the magnetically inequivalent sites in the AF phase near 10 K is plotted as function of θ. For the measurements at 9.0 T, a good fit to ∆ν is given by: ∆ν = 149.01 ± 1.86 cos(θ) + 0.01 cos(2θ) ∓ 0.03 cos(3θ).…”

“…All of the NMR results reported here were performed on the 7 Li nuclei using standard spin-echo techniques carried out with a spectrometer and probes built at UCLA. The NMR spectra were obtained by frequency-shifted and summed Fourier transform processing 7 with fixed applied magnetic fields between 9.0 and 44.5 Tesla.…”

“…They generate a corresponding magnetic field B i at the i-th 7 Li sites, which can be calculated for a given AF moment configuration. Depending on the configuration of the AF state, B i may have a sequence of values at different 7 Li sites or be given by a single value for all of them.…”

“…As T decreases below 23 K, there is an increase in T caused by the AF field "detuning" the 7 Li spins. Although it should be present, this mechanism is clearly not the dominant one for T for such an increase in T caused by other mechanisms, or (3) an enhancement of the spin-spin interactions between the nuclei being measured.…”

Emergence of charge order from the vortex state of a high-temperature superconductor

“…Standard spin-echo techniques were used with heterodyne spectrometers. Spectra were obtained at fixed magnetic fields by combining Fourier transforms of the spin-echo signal recorded for regularly spaced frequency values 40 .…”