Magnetization-recovery experiments for static and MAS-NMR of I=3/2 nuclei

Yesinowski, James P.

doi:10.1016/j.jmr.2006.02.004

Cited by 17 publications

(10 citation statements)

References 24 publications

(49 reference statements)

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“…36 For perfect cubic crystals (and sometimes also for imperfect cubic crystals), W avg 1 can be regarded as equal to W avg 2 , and the relaxation behavior approaches a single exponential. 30,[37][38][39][40] In addition, MAS activates zero-crossing conditions between ST and CT during the rotation periods (firstorder spin-exchange transitions), 28,29,32,34 adding a further relaxation channel, increasing the apparent magnetic relaxation rate. 34 On top of that, the local distortions in the 23 Na sites of the α-NaYF 4 NPs, as previously described, would lead to a distribution of relaxation rates, adding further dispersion in the magnetization recovery data.…”

Section: Xrd and Temmentioning

confidence: 99%

Probing Surface Effects on α-NaYF₄ Nanoparticles by Nuclear Magnetic Resonance

et al. 2020

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Section: Xrd and Temmentioning

confidence: 99%

Probing Surface Effects on α-NaYF₄ Nanoparticles by Nuclear Magnetic Resonance

et al. 2020

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“…3(a) depicts the two rate constants W 1 and W 2 characterizing the singleand double-quantum quadrupolar relaxation processes, respectively, and the single rate constant W characterizing the magnetic (Korringa) relaxation process. Since [38], the single-exponential time constant T 1 obtained from fitting the saturation-recovery intensities (with complete saturation of all three transitions, a condition that was shown to be necessary to obtain physically-meaningful 71 Ga relaxation results [26]) at each frequency in the spectrum obeys the equation [38] 1/T 1 = 2W 1 + 2W . Thus, subtracting the quadrupolar relaxation term, measured at the zero-Knight shift peak, from the measured 1/T 1 at any given frequency position in the spectrum yields 1/T 1,K (= 2W ), the Korringa relaxation rate [18] (making the reasonable assumption that the quadrupolar relaxation term is constant across the Knight-shifted spectrum) [39].…”

Section: Comparison Of Electronic Projected Densities Of States Atmentioning

confidence: 99%

Spatially correlated distributions of local metallic properties in bulk and nanocrystalline GaN

et al. 2017

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We compare local electronic structure at different atom types of a metallic semiconductor in bulk and nanocrystalline form. Multinuclear magic-angle-spinning nuclear magnetic resonance (MAS NMR) establishes that GaN synthesized as an intentionally-doped bulk powder or as annealed nanocrystalline particles exhibits metallic behavior and a wide distribution of differing electronic environments in both forms. Bulk polycrystalline wurtzite GaN doped with 0.13% Ge as a shallow donor exhibits a temperature-independent distribution of 71 Ga Knight shifts over the temperature range 123-473 K. Each Knight shift frequency in the inhomogeneously-broadened spectrum is characterized by a 71 Ga spin-lattice relaxation time T 1 that is in good agreement with the value predicted by the Knight-Korringa relation across the broad range of temperatures. The14 N spectrum shows a slightly smaller Knight shift distribution with spin-lattice relaxation time T 1 values at 295 K across the distribution also in good agreement with the Knight-Korringa relation. Similarly, annealed nanocrystalline wurtzite GaN (50-100 nm, and without Ge) exhibits a 71 Ga Knight shift distribution and T 1values (at 295 K) that follow the same Knight-Korringa behavior. Thus, both bulk and nanocrystalline forms of GaN are n-type and well above the metal-insulator transition (MIT), the nanocrystals most likely as a result of incorporation of shallow donor oxygen atoms during synthesis. Carriers in both forms of sample exhibit the near-ideal characteristics of a degenerate Fermi gas of non-interacting spins. The observation of NMR signals from both atom types, Ga and N, allows for the direct spatial correlation of the local electronic structure at the two sites in the lattice, specifically the s-orbital character of the electronic wavefunction of conduction band electrons at the Fermi edge. The relative values of these carrier wavefunction probabilities (nearly twice as great for the N atom as for the Ga) are in line with theoretical predictions. Analyses of 71 Ga, 14 N, and 15 N NMR results, including double-resonance 2D 15 N{ 71 Ga} measurements, reveal electronic disorder in the form of broad distributions of local metallic properties (Knight shifts) that are shown to be spatially correlated on a sub-nanometer scale.

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“…The thermal equilibrium is restored by i) randomly fluctuating magnetic fields (magnetic relaxation) and ii) randomly fluctuating EFGs (quadrupolar relaxation). Magnetic fluctuations are driven by hyperfine interactions, lattice motions, and dipole–dipole interactions . The magnetic relaxation mechanisms involve a single relaxation rate 3 W , 4 W , and drive single‐quantum (SQ) transitions between energy levels.…”

Section: Resultsmentioning

confidence: 99%

“…7(b)]. Equilibrium (c) and enhanced population distribution after the first excitation pulse (d) for CuFeS 2 and the corresponding quadrupolar W 1,2 and magnetic relaxation 3W, 4W pathways shown as arrows, after (27). with an appropriate phase cycling scheme can further reduce the measurement time.…”

Section: Resultsmentioning

confidence: 99%

AFNMR/NQR signal enhancement via population transfer

Lehmann-Horn

Miljak

2014

Concepts Magnetic Resonance

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Antiferromagnetic nuclear magnetic resonance (AFNMR) and nuclear quadrupole resonance (NQR) are useful techniques to characterize materials in bulk volumes without applying external static magnetic fields. For industrial materials characterization applications, it is crucial to maximize signal‐to‐noise ratio in the available time. We simulate the AFNMR and NQR signal enhancement via population transfer in single crystals and powders and predict the enhancement factors for half‐integer quadrupolar nuclei spin systems. Differences to conventional high‐field NMR population transfer experiments are emphasized. We restrict our discussion to electric field gradients with axial symmetry η = 0. Triple resonance tuned crossed coil experiments on CuFeS2 and In2O3 powders support the numerical results. © 2015 Wiley Periodicals, Inc. Concepts Magn Reson Part A 43A: 147–156, 2015.

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Magnetization-recovery experiments for static and MAS-NMR of I=3/2 nuclei

Cited by 17 publications

References 24 publications

Probing Surface Effects on α-NaYF₄ Nanoparticles by Nuclear Magnetic Resonance

Probing Surface Effects on α-NaYF₄ Nanoparticles by Nuclear Magnetic Resonance

Spatially correlated distributions of local metallic properties in bulk and nanocrystalline GaN

AFNMR/NQR signal enhancement via population transfer

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Magnetization-recovery experiments for static and MAS-NMR of I=3/2 nuclei

Cited by 17 publications

References 24 publications

Probing Surface Effects on α-NaYF4 Nanoparticles by Nuclear Magnetic Resonance

Probing Surface Effects on α-NaYF4 Nanoparticles by Nuclear Magnetic Resonance

Spatially correlated distributions of local metallic properties in bulk and nanocrystalline GaN

AFNMR/NQR signal enhancement via population transfer

Contact Info

Product

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About

Probing Surface Effects on α-NaYF₄ Nanoparticles by Nuclear Magnetic Resonance

Probing Surface Effects on α-NaYF₄ Nanoparticles by Nuclear Magnetic Resonance