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通过旋转的动态平均场理论对NMR信号的微观理解

Timo Gräßer1, Thomas Hahn2, Götz S Uhrig1

  • 1Condensed Matter Theory, TU Dortmund University, Otto-Hahn Straße 4, Dortmund, 44221, Germany.

Solid state nuclear magnetic resonance
|June 1, 2024
PubMed
概括

一个新的非局部动态平均场理论 (nl-spinDMFT) 准确地模拟了核自旋动力学和自由感应衰变 (FID). 这种方法提高了对CaF2和阿达曼坦等材料旋转行为的理解.

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NMR-active nuclei have energy levels called 'spin states' that are associated with the orientations of their nuclear magnetic moments. In the absence of a magnetic field, the nuclear magnetic moments are randomly oriented, and the spin states are degenerate. When an external magnetic field is applied, the spin states have only 2 + 1 orientations available to them. A proton with = ½ has two available orientations. Similarly, for a quadrupolar nucleus with a nuclear spin value of...
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In the absence of an external magnetic field, nuclear spin states are degenerate and randomly oriented. When a magnetic field is applied, the spins begin to precess and orient themselves along (lower energy) or against (higher energy) the direction of the field. At equilibrium, a slight excess population of spins exists in the lower energy state. Because the direction of the magnetic field is fixed as the z-axis,  the precessing magnetic moments are randomly oriented around the z-axis.
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The number of nuclear spins aligned in the lower energy state is slightly greater than those in the higher energy state. In the presence of an external magnetic field, as the spins precess at the Larmor frequency, the excess population results in a net magnetization oriented along the z axis. When a pulse or a short burst of radio waves at the Larmor frequency is applied along the x axis, the coupling of frequencies causes resonance and flips the nuclear spins of the excess population from the...
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