Destruction of the Spin Diffusion Barrier near Paramagnetic Impurities in Pure NQR

2002 ◽  
Vol 57 (6-7) ◽  
pp. 307-314 ◽  
Author(s):  
G. B. Furman ◽  
S. D. Goren
Keyword(s):  
Diffusion Process ◽  
Diffusion Barrier ◽  
Spin Diffusion ◽  
Double Resonance ◽  
Paramagnetic Impurities ◽  
Resonance Process

The double resonance process between nuclei inside and outside the spin diffusion barrier is considered. By applying two radiofrequency fields, both of the same amplitude, one rotating at the frequency ωS for nuclei inside of the diffusion barrier and one rotating at the frequency ωI for nuclei outside of the diffusion barrier, the Hartmann-Hahn condition will be reached, which results in conservation of the quadrupole energy in the spin diffusion process and destruction of the spin diffusion barrier. This technique can be used to detect NQR signals from nuclei near paramagnetic impurities.

Scaling analyses for hyperpolarization transfer across a spin-diffusion barrier and into bulk solid media

2021 ◽  
Author(s):  
Nathan A. Prisco ◽  
Arthur C. Pinon ◽  
Lyndon Emsley ◽  
Bradley F. Chmelka
Keyword(s):  
Diffusion Barrier ◽  
Spin Diffusion ◽  
Energy Transport ◽  
Bulk Solid ◽  
Solid Media ◽  
Scaling Analyses ◽  
Rate Limiting

Quantitative scaling analyses based on mass and energy transport analogies enable rate-limiting processes to be established in hyperpolarization transfer phenomena.

scholarly journals Three-spin solid effect and the spin diffusion barrier in amorphous solids

2019 ◽  
Vol 5 (7) ◽  
pp. eaax2743 ◽  
Author(s):  
Kong Ooi Tan ◽  
Michael Mardini ◽  
Chen Yang ◽  
Jan Henrik Ardenkjær-Larsen ◽  
Robert G. Griffin
Keyword(s):  
Diffusion Barrier ◽  
Nuclear Polarization ◽  
Spin Diffusion ◽  
Amorphous Solids ◽  
Second Step ◽  
Intimate Contact ◽  
Glycerol Water ◽  
Water Matrix ◽  
Solid Effect ◽  
Trityl Radical

Dynamic nuclear polarization (DNP) has evolved as the method of choice to enhance NMR signal intensities and to address a variety of otherwise inaccessible chemical, biological and physical questions. Despite its success, there is no detailed understanding of how the large electron polarization is transferred to the surrounding nuclei or where these nuclei are located relative to the polarizing agent. To address these questions we perform an analysis of the three-spin solid effect, and show that it is exquisitely sensitive to the electron-nuclear distances. We exploit this feature and determine that the size of the spin diffusion barrier surrounding the trityl radical in a glassy glycerol–water matrix is <6 Å, and that the protons involved in the initial transfer step are on the trityl molecule. 1H ENDOR experiments indicate that polarization is then transferred in a second step to glycerol molecules in intimate contact with the trityl.

scholarly journals Structures of Impurity Defects in Lithium Niobate and Tantalate Derived from Electron Paramagnetic and Electron Nuclear Double Resonance Data

Crystals ◽  
2021 ◽  
Vol 11 (4) ◽  
pp. 339
Author(s):  
Valentin G. Grachev ◽  
Galina I. Malovichko
Keyword(s):  
Lithium Niobate ◽  
Double Resonance ◽  
Charge Compensation ◽  
Dipole Approximation ◽  
Structural Vacancy ◽  
Electron Nuclear Double Resonance ◽  
Paramagnetic Resonance ◽  
Paramagnetic Impurities ◽  
Impurity Defect ◽  
Electron Paramagnetic

Point intrinsic and extrinsic defects, especially paramagnetic ions of transition metals and rare-earth elements, have essential influence on properties of lithium niobate, LN and tantalate, LT, and often determine their suitability for numerous applications. Discussions about structures of the defects in LN/LT have lasted for decades. Many experimental methods facilitate progress in determining the structures of impurity centers. This paper gives current bird’s eye view on contributions of Electron Paramagnetic Resonance (EPR), and Electron Nuclear Double Resonance (ENDOR) studies to the determination of impurity defect structures in LN and LT crystals for a broad audience of researchers and students. Symmetry and charge compensation considerations restrict a number of possible structures. Comparison of measured angular dependences of ENDOR frequencies with calculated ones for Li and Nb substitution using dipole–dipole approximation allows unambiguously to determine the exact location of paramagnetic impurities. Models with two lithium vacancies explain angular dependencies of EPR spectra for Me3+ ions substituting for Li+ like Cr, Er, Fe, Gd, Nd, and Yb. Self-compensation of excessive charges through equalization of concentrations of Me3+(Li+) and Me3+(Nb5+) and appearance of interstitial Li+ in the structural vacancy near Me3+(Nb5+) take place in stoichiometric LN/LT due to lack of intrinsic defects.

Electron-driven spin diffusion supports crossing the diffusion barrier in MAS DNP

2018 ◽  
Vol 20 (16) ◽  
pp. 11418-11429 ◽  
Author(s):  
Johannes J. Wittmann ◽  
Michael Eckardt ◽  
Wolfgang Harneit ◽  
Björn Corzilius
Keyword(s):  
Dynamic Nuclear Polarization ◽  
Diffusion Barrier ◽  
Nuclear Polarization ◽  
Spin Diffusion ◽  
Hyperfine Interactions ◽  
Magic Angle Spinning ◽  
Magic Angle ◽  
Diffusion Rates ◽  
Angle Spinning

Hyperfine interactions can quench homonuclear spin-diffusion in the direct vicinity of a polarizing agent in dynamic nuclear polarization (DNP). However, under magic-angle spinning (MAS), the same interactions may also enhance the spin-diffusion rates through an electron-driven spin diffusion (EDSD) mechanism introduced here.

Spin diffusion in multiple pulse spin-locking in solids containing paramagnetic impurities

2010 ◽  
Vol 38 (4) ◽  
pp. 84-89
Author(s):  
G.B. Furman ◽  
S.D. Goren ◽  
A.M. Panich ◽  
A.I. Shames ◽  
T. Nakajima
Keyword(s):  
Spin Diffusion ◽  
Multiple Pulse ◽  
Paramagnetic Impurities ◽  
Spin Locking

scholarly journals Direct observation of hyperpolarization breaking through the spin diffusion barrier

2021 ◽  
Vol 7 (18) ◽  
pp. eabf5735
Author(s):  
Quentin Stern ◽  
Samuel François Cousin ◽  
Frédéric Mentink-Vigier ◽  
Arthur César Pinon ◽  
Stuart James Elliott ◽  
...  
Keyword(s):  
Diffusion Barrier ◽  
Nuclear Polarization ◽  
Spin Diffusion ◽  
Magic Angle Spinning ◽  
Resonance Spectroscopy ◽  
Magic Angle ◽  
Paramagnetic Centers ◽  
Static Mode ◽  
Angle Spinning ◽  
Marked Dependence

Dynamic nuclear polarization (DNP) is a widely used tool for overcoming the low intrinsic sensitivity of nuclear magnetic resonance spectroscopy and imaging. Its practical applicability is typically bounded, however, by the so-called “spin diffusion barrier,” which relates to the poor efficiency of polarization transfer from highly polarized nuclei close to paramagnetic centers to bulk nuclei. A quantitative assessment of this barrier has been hindered so far by the lack of general methods for studying nuclear polarization flow in the vicinity of paramagnetic centers. Here, we fill this gap and introduce a general set of experiments based on microwave gating that are readily implemented. We demonstrate the versatility of our approach in experiments conducted between 1.2 and 4.2 K in static mode and at 100 K under magic angle spinning (MAS)—conditions typical for dissolution DNP and MAS-DNP—and directly observe the marked dependence of polarization flow on temperature.

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