NMR measurements of power-law behavior in the spin-wave and critical regions of ferromagnetic EuO

Abstract

Precision continuous-wave NMR measurements have been carried out over the entire magnetization curve of EuO and are presented in tabular form. Two very closely spaced resonances are observed and are attributed to domain and domain-wall signals. Both of the signals are useful for analysis in the spin-wave region. Only the domain signal is measurable above ∼50 K. The latter is used for fitting Tc and the critical exponent β. The critical-region fits agree with previous measurements within experimental error. The low-temperature data exhibit a clear-cut T2 behavior, at variance with the expectations of conventional spin-wave theory. This result is discussed in relation to two semiempirical spin-wave schemes, one formulated by Bykovetz, and one by Koebler. The NMR signal at 4.2 K gives no indication of a quadrupole splitting in contradiction to the interpretation of several previous spin-echo NMR spectra observed in EuO. This issue remains unresolved.