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 (Herve & Pescia, 1960a,b).