Model for domain and domain wall NMR signals in magnetic materials

摘要

Spin echo NMR signals in magnetic materials( simple metals, alloys or intermetallic compounds) generally result from mixed contributions of distinct regions of the sample, the magnetic domains and the domains walls. The amplitude of the signal is proportional to the so-called enhancement factor which in the most of the cases greatly differs in these two regions, depending upon the wall mobility, the magnetic anisotropy, etc. The experimental access to domain and domain walls is possible, in principle, by a careful control of the RF power applied to the sample. In this paper a simple superposition model is proposed which includes both contributions to the NMR signal. We calculate the amplitude of the spin echo in magnetic powder samples and compare with experimental situations where it has been possible to separate different contributions to the signals. This has been done in some R Co(sub 2) magnetic rare earth intermetallic compounds by analysing the spectral linewidths and the curve of spin echo amplitude vs. the applied RF field. Despite its simplicity, the present model allows the understanding of the main features of the NMR spectra and the dependence of the echo amplitude with the RF power in these compounds. (author). 15 refs., 5 figs.