Improvement in the Measurement of Spin-Lattice Relaxation Time in Electron Paramagnetic Resonance

Abstract

The spin-lattice, or longitudinal, relaxation time T ₁ plays an important role in magnetic resonance because it provides significant information about the coupling of a paramagnetic ion with its environment via its dependence on such factors as temperature, frequency (Scott & Jefferies, 1962; Kurtz & Stapleton, 1980), spin concentration (Gill, 1962), and magnetic field (Albart & Pescia, 1980; Nogatchewsky et al., 1977). But the measurement of electronic spin-lattice relaxation times is problematic because the times span the range from the very short (10⁻¹⁵ s) to the very long (1 s; cf. Pescia, 1966). The one microsecond spin-lattice relaxation time demarcates “short” from “long” relaxation times, which traditionally have each required their own methods of measurement. For example, long relaxation times are measured by using cw-EPR spectrometers to record spectra at multiple power levels near and under the condition of saturation; the spin-spin and spin-lattice relaxation times are then calculated from lineshape parameters. But the so-called short relaxation times are not measurable on the time scale of common cw-EPR instrumental detection methods. Short spin-lattice relaxation times are therefore measured by resorting to different (i.e., transient) magnetic resonance techniques such as pulsed saturation, spin echo (cf. Poole & Farach, 1971), and amplitude modulation (Hervé & Pescia, 1960a,b).

This chapter is a partial translation of the doctoral thesis of Robert Lopez entitled, “Amélioration de la mesure du temps de relaxation spin-réseau T1 en résonance paramagnétique électronique: Application a l’acetat de cuivre calcium dilué et un verre boraté dopé Fe2O3,” Paul Sabatier University, Toulouse, France (1993) with permission.

Translated by Sushil K. Misra

Physics Department, Concordia University, 1455 de Maisonneuve Boulevard West, Montreal, Quebec H3G 1M8, Canada