An inelastic neutron scattering study of single-crystal heavy-fermion YbAgGe

Abstract

Single crystals of the heavy-fermion compound YbAgGe have been studied by\nneutron scattering. The magnetic ordering occurring below T1=0.5 K is\ncharacterized by a commensurate propagation vector k=(1/3,0,1/3) and the\nmoments in the basal plane of the hexagonal structure. The dynamic magnetic\nsusceptibility is dominated by quasielastic spin fluctuations with a\ncharacteristic energy Gamma of the order of 1 meV. The spins fluctuate\npredominantly in the basal plane. No spin-wave excitations are observed in the\nmagnetically ordered phase. Below the Kondo temperature, TK=20 K, Gamma shows a\nstrong q dependence for wave vectors along the c* direction, but is\nq-independent in the basal plane. Gamma shows initially a rapid increase with\ntemperature T at the antiferromagnetic zone center, but follows a standard\nsqrt(T) law for other q values and for T>TK in general. These observations\nclassify YbAgGe as a well-behaved heavy-fermion compound with a particular\nq-dependence of the antiferromagnetic spin fluctuations, possibly related to\nthe geometrical frustration of the Yb3+ ions.\n