Separation of quadrupolar and magnetic contributions to spin-lattice relaxation in the case of a single isotope

TL;DR

This paper introduces a novel NMR pulse double-irradiation technique to distinguish magnetic and quadrupolar contributions to spin-lattice relaxation, demonstrated on 17O in a high-temperature superconductor, providing a quantitative and heating-free analysis.

Contribution

A new NMR method that separates magnetic and quadrupolar relaxation contributions using a specific pulse sequence, applicable to single isotope samples.

Findings

Successfully separated magnetic and quadrupolar contributions in 17O NMR.

Validated the method with analytical calculations and experimental cross-checks.

Demonstrated the technique on high-temperature superconductor YBa2Cu4O8.

Abstract

We present a NMR pulse double-irradiation method which allows one to separate magnetic from quadrupolar contributions in the spin-lattice relaxation. The pulse sequence fully saturates one transition while another is observed. In the presence of a Delta m = 2 quadrupolar contribution, the intensity of the observed line is altered compared to a standard spin-echo experiment. We calculated analytically this intensity change for spins I=1, 3/2, 5/2, thus providing a quantitative analysis of the experimental results. Since the pulse sequence we used takes care of the absorbed radio-frequency power, no problems due to heating arise. The method is especially suited when only one NMR sensitive isotope is available. Different cross-checks were performed to prove the reliability of the obtained results. The applicability of this method is demonstrated by a study of the plane oxygen 17O (I = 5/2) in the high-temperature superconductor YBa_2Cu_4O_8: the 17O spin-lattice relaxation rate consists of magnetic as well as quadrupolar contributions.