Interplay of quadrupolar order, Ce?4f spin dynamics and RKKY induced conduction electron spin polarization in CeAg

We report on measurements of the Knight shift K and spin–lattice relaxation rate λ of positive muons (μ+) implanted in cubic CeAg, a compound which is known to possess ferromagnetic ( K) and ferroquadrupolar (TQ = 15–16 K) order. The zero field (ZF) λ implies randomly and isotropically fluctuating Ce 4f moments above TQ which show a trend to a, perhaps critical, slowing down on approaching TQ. Below TQ the fluctuations are restricted to the now tetragonally distorted axis of CeAg. In a longitudinal field the generally isotropic fluctuations show a tendency towards freezing near Tc, not TQ. The Knight shift results reveal an anisotropic contact hyperfine coupling parameter Ac, which displays abrupt changes at Tc. ZF measurements below Tc reveal the presence of discrete spontaneous internal fields. The results on λ and Ac are interpreted as arising from quadrupolar effects, concerning in particular the induced spin polarization of the conduction electron system.