Primary Nuclear Spin Echoes in EPR Induced by Microwave Pulses

Abstract

Primary nuclear spin echoes in electron-nuclear spin systems, created and detected by exciting electron-spin transitions only, are presented. Two pulse sequences for the generation of this new type of echo in magnetic resonance are proposed. The first sequence consists of twosemi-selectivemicrowave pulses with flip angles π and 2π followed by a weak microwave probe pulse for detection. It is noteworthy that the flip angles are doubled compared to that used in the usual primary spin-echo experiment. In the second sequence, the nuclear spin echo is created by nonselective microwave pulses and observed as a modulation on top of the electron spin echo. Both experiments are analyzed theoretically by using the product-operator formalism. The predicted features are verified experimentally, in particular, the separation of the primary echoes from the coherence-transfer echoes by using two-dimensional representations of the data in the frequency domain. As an example of application, the determination of the phase-memory time of nuclei coupled to the electron spin is discussed.