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 ( T Q = 15–16 K) order. The zero field (ZF) λ implies randomly and isotropically fluctuating Ce 4f moments above T Q which show a trend to a, perhaps critical, slowing down on approaching T Q . Below T Q 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 T c , not T Q . The Knight shift results reveal an anisotropic contact hyperfine coupling parameter A c , which displays abrupt changes at T c . ZF measurements below T c reveal the presence of discrete spontaneous internal fields. The results on λ and A c are interpreted as arising from quadrupolar effects, concerning in particular the induced spin polarization of the conduction electron system.