SPIN-DENSITY-WAVE OF ITINERANT HEAVY ELECTRONS IN CE(RU0.85RH0.15)(2)SI-2

The magnetic properties of Ce(Ru0.85Rh0.15)(2)Si-2 were studied by neu tron scattering and measurements of magnetization, susceptibility, spe cific heat and thermal expansion as a function of temperature. We obse rve a crossover from a high temperature localized spin to a low temper ature heavy electron state. Spin density wave (SDW) behavior appears i n the heavy electron state below T-N = 5.5 K and the volume change due to spin quantum fluctuations associated with the SDW and the Kondo sc reening is reminiscent of moment-volume instabilities of the INVAR and anti-INVAR behavior of 3 d transition metal alloys.