Muon depolarization by the spin density wave hyperfine fields of lead

Abstract

Muon depolarization arising from hyperfine fields created by the twelve SDWs in Pb is studied. Since the SDW wave vectors,$\vec Q_i$={210}, are commensurate with the lattice, there are no hyperfine fields at the octahedral interstitial sites (where muons ordinarily reside). Instead, the SDWs have antinodes at the tetrahedral interstitial sites and generateμ ⁺ hyperfine fields estimated to be ∼ 3000 G. Recent data show that the depolarization rate in Pb falls sharply towards zero at 35K (on account ofμ ⁺ diffusion), but then slowly recovers to half its low temperature value near 200 K. Such recovery of the depolarization rate can be attributed to growth of the thermally activated occupation probability for muons at tetrahedral sites, where their spins undergo (motionally narrowed) transient precession caused by the static 3000 G fields. SDW depolarization can be distinguished from recovery caused by deep traps. A 10 G longitudinal field will quench the latter but not the former. Such an experiment could provide a crucial confirmation of the exotic magnetism of Pb.