Exchange Enhancement of Conduction Electron Spin Lifetimes in ZrZn1.9

Abstract

The magnetic resonance originally observed by Ogawa in the ferromagnetic regime of ZrZn₂ powder has been reinvestigated in thin plates of ZrZn_1.9 of maximal Curie temperature and magnetization, at several microwave frequencies and over a wide temperature range extending well into the paramagnetic region. A g‐value g = 1.98±0.01 is found at all frequencies and temperatures when demagnetization effects are taken into account. Well above the Curie temperature the resonance broadens rapidly and independently of frequency, following the Curie‐Weiss behavior of the susceptibility. We attribute this width entirely to lifetime (spin‐lattice) broadening as in the conduction electron spin resonance of normal metals but here subject to strong exchange enhancement. The deduced ``uncoupled'' relaxation time is crudely consistent with an estimated transport collision frequency and the degree of spin‐orbit coupling indicated by the small g shift. Extrapolation of the relaxation mechanism into the ordered regime predicts a linewidth proportional to the observation frequency roughly as observed, through an additional orientation dependent broadening contribution appears at the lowest temperatures.